pgsql-performance.200209

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-- 

Keith Gray
Technical Services Manager
Heart Consulting Services


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------------------------------------------------------------------------------
 > Khusus Pelanggan Telepon DIVRE 2, Tekan 166 untuk mendengarkan pesan Anda
 ------------------------------------------------------------------------------

From pgsql-performance-owner@postgresql.org  Fri Sep 13 20:16:03 2002
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From: Justin Clift <justin@postgresql.org>
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Hi everyone,

There are PostgreSQL servers around that are handling 2,000 simultaneous
client connections (in real life) without problems, but no-one obvious
seems to have yet taken the time to do fine grained testing of the
servers which can take this kind of load, to accurately model their
performance characteristics.

Does anyone here happen to have fine grained benchmark/performance
figures hanging around which get into this range of performance? 
Preferably with pretty precise details of how the system was configured,
etc.

:-)

Regards and best wishes,

Justin Clift

-- 
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
   - Indira Gandhi

From pgsql-performance-owner@postgresql.org  Tue Sep 17 06:50:17 2002
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------------------------------------------------------------------------------
 > Khusus Pelanggan Telepon DIVRE 2, Tekan 166 untuk mendengarkan pesan Anda
 ------------------------------------------------------------------------------

From pgsql-general-owner@postgresql.org  Thu Sep 26 04:35:33 2002
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From: "Shridhar Daithankar" <shridhar_daithankar@persistent.co.in>
To: pgsql-hackers@postgresql.org, pgsql-general@postgresql.org
Date: Thu, 26 Sep 2002 14:05:44 +0530
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Subject: Performance while loading data and indexing
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Hello all,

Some time back I posted a query to build a site with 150GB of database. In last 
couple of weeks, lots of things were tested at my place and there are some 
results and again some concerns. 

This is a long post. Please be patient and read thr. If we win this, I guess we 
have a good marketing/advocacy  case here..;-)

First the problems (For those who do not read beyond first page)

1) Database load time from flat file using copy is very high
2) Creating index takes huge amount of time.
3) Any suggsestions for runtime as data load and query will be going in 
parallel.

Now the details. Note that this is a test run only..

Platform:- 4x Xeon2.4GHz/4GB RAM/4x48 SCSI RAID5/72 GB SCSI
RedHat7.2/PostgreSQL7.1.3

Database in flat file: 
125,000,000 records of around 100 bytes each. 
Flat file size 12GB

Load time: 14581 sec/~8600 rows persec/~ an MB of data per sec.
Create unique composite index on 2 char and a timestamp field:  25226 sec.
Database size on disk: 26GB
Select query: 1.5 sec. for approx. 150 rows.

Important postgresql.conf settings

sort_mem = 12000
shared_buffers = 24000
fsync=true (Sad but true. Left untouched.. Will that make a difference on 
SCSI?)
wal_buffers = 65536 
wal_files = 64 

Now the requirements

Initial flat data load: 250GB of data. This has gone up since last query. It 
was 150GB earlier..
Ongoing inserts: 5000/sec. 
Number of queries: 4800 queries/hour
Query response time: 10 sec.


Now questions.

1)  Instead of copying from a single 12GB data file,  will a parallel copy from 
say 5 files will speed up the things? 

Couple MB of data per sec. to disk is just not saturating it. It's a RAID 5 
setup..

2) Sort mem.=12K i.e. 94MB, sounds good enough to me. Does this need further 
addition to improve create index performance?

3) 5K concurrent inserts with an index on, will this need a additional CPU 
power? Like deploying it on dual RISC CPUs etc? 

4) Query performance is not a problem. Though 4.8K queries per sec. expected 
response time from each query is 10 sec. But my guess is some serius CPU power 
will be chewed there too..

5)Will upgrading to 7.2.2/7.3 beta help?

All in all, in the  test, we didn't see the performance where hardware is 
saturated to it's limits. So effectively we are not able to get postgresql 
making use of it. Just pushing WAL and shared buffers does not seem to be the 
solution.

If you guys have any suggestions. let me know.  I need them all..

Mysql is almost out because it's creating index for last 17 hours. I don't 
think it will keep up with 5K inserts per sec. with index. SAP DB is under 
evaluation too. But postgresql is most favourite as of now because it works. So 
I need to come up with solutions to problems that will occur in near future..
;-)

TIA..

Bye
 Shridhar

--
Law of Procrastination:	Procrastination avoids boredom; one never has	the 
feeling that there is nothing important to do.


From pgsql-general-owner@postgresql.org  Thu Sep 26 04:53:43 2002
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From: "Shridhar Daithankar" <shridhar_daithankar@persistent.co.in>
To: pgsql-hackers@postgresql.org, pgsql-general@postgresql.org
Date: Thu, 26 Sep 2002 14:24:02 +0530
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Subject: Re: [HACKERS] Performance while loading data and indexing
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On 26 Sep 2002 at 14:05, Shridhar Daithankar wrote:
> Some time back I posted a query to build a site with 150GB of database. In last 
> couple of weeks, lots of things were tested at my place and there are some 
> results and again some concerns. 

> 2) Creating index takes huge amount of time.
> Load time: 14581 sec/~8600 rows persec/~ an MB of data per sec.
> Create unique composite index on 2 char and a timestamp field:  25226 sec.
> Database size on disk: 26GB
> Select query: 1.5 sec. for approx. 150 rows.

> 2) Sort mem.=12K i.e. 94MB, sounds good enough to me. Does this need further 
> addition to improve create index performance?

Just a thought. If I sort the table before making an index, would it be faster 
than creating index on raw table? And/or if at all, how do I sort the table 
without duplicating it?

Just a wild thought..

Bye
 Shridhar

--
linux: the choice of a GNU generation(ksh@cis.ufl.edu put this on Tshirts in 
'93)


From pgsql-general-owner@postgresql.org  Thu Sep 26 05:06:18 2002
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From: Martijn van Oosterhout <kleptog@svana.org>
To: Shridhar Daithankar <shridhar_daithankar@persistent.co.in>
Cc: pgsql-hackers@postgresql.org, pgsql-general@postgresql.org
Subject: Re: Performance while loading data and indexing
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I'll preface this by saying that while I have a large database, it doesn't
require quite the performace you're talking about here.

On Thu, Sep 26, 2002 at 02:05:44PM +0530, Shridhar Daithankar wrote:
> 1) Database load time from flat file using copy is very high
> 2) Creating index takes huge amount of time.
> 3) Any suggsestions for runtime as data load and query will be going in 
> parallel.

You're loading all the data in one copy. I find that INSERTs are mostly
limited by indexes. While index lookups are cheap, they are not free and
each index needs to be updated for each row.

I fond using partial indexes to only index the rows you actually use can
help with the loading. It's a bit obscure though.

As for parallel loading, you'll be limited mostly by your I/O bandwidth.
Have you measured it to take sure it's up to speed?

> Now the details. Note that this is a test run only..
> 
> Platform:- 4x Xeon2.4GHz/4GB RAM/4x48 SCSI RAID5/72 GB SCSI
> RedHat7.2/PostgreSQL7.1.3
> 
> Database in flat file: 
> 125,000,000 records of around 100 bytes each. 
> Flat file size 12GB
> 
> Load time: 14581 sec/~8600 rows persec/~ an MB of data per sec.
> Create unique composite index on 2 char and a timestamp field:  25226 sec.
> Database size on disk: 26GB
> Select query: 1.5 sec. for approx. 150 rows.

So you're loading at a rate of 860KB per sec. That's not too fast. How many
indexes are active at that time? Triggers and foreign keys also take their
toll.

> Important postgresql.conf settings
> 
> sort_mem = 12000
> shared_buffers = 24000
> fsync=true (Sad but true. Left untouched.. Will that make a difference on 
> SCSI?)
> wal_buffers = 65536 
> wal_files = 64 

fsync IIRC only affects the WAL buffers now but it may be quite expensive,
especially considering it's running on every transaction commit. Oh, your
WAL files are on a seperate disk from the data?

> Initial flat data load: 250GB of data. This has gone up since last query. It 
> was 150GB earlier..
> Ongoing inserts: 5000/sec. 
> Number of queries: 4800 queries/hour
> Query response time: 10 sec.

That looks quite acheivable.

> 1)  Instead of copying from a single 12GB data file,  will a parallel copy from 
> say 5 files will speed up the things? 

Limited by I/O bandwidth. On linux vmstat can tell you how many blocks are
being loaded and stored per second. Try it. As long as sync() doesn't get
done too often, it should be help.

> Couple MB of data per sec. to disk is just not saturating it. It's a RAID 5 
> setup..

No, it's not. You should be able to do better.

> 2) Sort mem.=12K i.e. 94MB, sounds good enough to me. Does this need further 
> addition to improve create index performance?

Should be fine. Admittedly your indexes are taking rather long to build.

> 3) 5K concurrent inserts with an index on, will this need a additional CPU 
> power? Like deploying it on dual RISC CPUs etc? 

It shouldn't. Do you have an idea of what your CPU usage is? ps aux should
give you a decent idea.

> 4) Query performance is not a problem. Though 4.8K queries per sec. expected 
> response time from each query is 10 sec. But my guess is some serius CPU power 
> will be chewed there too..

Should be fine.

> 5)Will upgrading to 7.2.2/7.3 beta help?

Possibly, though it may be wirth it just for the features/bugfixes.

> All in all, in the  test, we didn't see the performance where hardware is 
> saturated to it's limits. So effectively we are not able to get postgresql 
> making use of it. Just pushing WAL and shared buffers does not seem to be the 
> solution.
> 
> If you guys have any suggestions. let me know.  I need them all..

Find the bottleneck: CPU, I/O or memory?

> Mysql is almost out because it's creating index for last 17 hours. I don't 
> think it will keep up with 5K inserts per sec. with index. SAP DB is under 
> evaluation too. But postgresql is most favourite as of now because it works. So 
> I need to come up with solutions to problems that will occur in near future..
> ;-)

17 hours! Ouch. Either way, you should be able to do much better. Hope this
helps,
-- 
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> There are 10 kinds of people in the world, those that can do binary
> arithmetic and those that can't.

From pgsql-hackers-owner@postgresql.org  Thu Sep 26 05:12:58 2002
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From: "Shridhar Daithankar" <shridhar_daithankar@persistent.co.in>
To: paolo.cassago@talentmanager.com
Date: Thu, 26 Sep 2002 14:43:20 +0530
MIME-Version: 1.0
Subject: Re: Performance while loading data and indexing
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On 26 Sep 2002 at 10:51, paolo.cassago@talentmanager.c wrote:

> Hi,
>     it seems you have to cluster it, I don't think you have another choise.

Hmm.. That didn't occur to me...I guess some real time clustering like usogres 
would do. Unless it turns out to be a performance hog..

But this is just insert and select. No updates no deletes(Unless customer makes 
a 180 degree turn) So I doubt if clustering will help. At the most I can 
replicate data across machines and spread queries on them. Replication overhead 
as a down side and low query load on each machine as upside..

> I'm retrieving the configuration of our postgres servers (I'm out of office
> now), so I can send it to you. I was quite disperate about performance, and
> I was thinking to migrate the data on an oracle database. Then I found this
> configuration on the net, and I had a succesfull increase of performance.

In this case, we are upto postgresql because we/our customer wants to keep the 
costs down..:-) Even they are asking now if it's possible to keep hardware 
costs down as well. That's getting some funny responses here but I digress..

> Maybe this can help you.
> 
> Why you use copy to insert records? I usually use perl scripts, and they
> work well .

Performance reasons. As I said in one of my posts earlier, putting upto 100K 
records in one transaction in steps of 10K did not reach performance of copy. 
As Tom said rightly, it was a 4-1 ratio despite using transactions..

Thanks once again..
Bye
 Shridhar

--
Secretary's Revenge:	Filing almost everything under "the".


From pgsql-general-owner@postgresql.org  Thu Sep 26 05:17:41 2002
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From: Justin Clift <justin@postgresql.org>
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Subject: Re: Performance while loading data and indexing
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Hi Shridhar,

Shridhar Daithankar wrote:
<snip>
> 3) Any suggsestions for runtime as data load and query will be going in
> parallel.

That sounds unusual.  From reading this, it *sounds* like you'll be
running queries against an incomplete dataset, or maybe just running the
queries that affect the tables loaded thus far (during the initial
load).

<snip>
> fsync=true (Sad but true. Left untouched.. Will that make a difference on
> SCSI?)

Definitely.  Have directly measured a ~ 2x tps throughput increase on
FreeBSD when leaving fsync off whilst performance measuring stuff
recently (PG 7.2.2).  Like anything it'll depend on workload, phase of
moon, etc, but it's a decent indicator.

<snip>
> Now questions.
> 
> 1)  Instead of copying from a single 12GB data file,  will a parallel copy from
> say 5 files will speed up the things?

Not sure yet.  Haven't get done enough performance testing (on the cards
very soon though).

> Couple MB of data per sec. to disk is just not saturating it. It's a RAID 5
> setup..

fsync = off would help during the data load, but not a good idea if
you're going to be running queries against it at the same time.

Am still getting the hang of performance tuning stuff.  Have a bunch of
Ultra160 hardware for the Intel platform, and am testing against it as
time permits.

Not as high end as I'd like, but it's a start.

:-)

Regards and best wishes,

Justin Clift

<snip>
> Bye
>  Shridhar

-- 
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
   - Indira Gandhi

From pgsql-general-owner@postgresql.org  Thu Sep 26 05:35:14 2002
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From: "Shridhar Daithankar" <shridhar_daithankar@persistent.co.in>
To: pgsql-hackers@postgresql.org, pgsql-general@postgresql.org
Date: Thu, 26 Sep 2002 15:05:40 +0530
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Subject: Re: Performance while loading data and indexing
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On 26 Sep 2002 at 19:17, Justin Clift wrote:
> Shridhar Daithankar wrote:
> <snip>
> > 3) Any suggsestions for runtime as data load and query will be going in
> > parallel.
> 
> That sounds unusual.  From reading this, it *sounds* like you'll be
> running queries against an incomplete dataset, or maybe just running the
> queries that affect the tables loaded thus far (during the initial
> load).

That's correct. Load the data so far and keep inserting data as and when it 
generates.

They don't mind running against data so far. It's not very accurate stuff 
IMO...

> > fsync=true (Sad but true. Left untouched.. Will that make a difference on
> > SCSI?)
> 
> Definitely.  Have directly measured a ~ 2x tps throughput increase on
> FreeBSD when leaving fsync off whilst performance measuring stuff
> recently (PG 7.2.2).  Like anything it'll depend on workload, phase of
> moon, etc, but it's a decent indicator.

I didn't know even that matters with SCSI..Will check out..

> fsync = off would help during the data load, but not a good idea if
> you're going to be running queries against it at the same time.

That's OK for the reasons mentioned above. It wouldn't be out of place to 
expect a UPS to such an installation...

Bye
 Shridhar

--
Hoare's Law of Large Problems:	Inside every large problem is a small problem 
struggling to get out.


From pgsql-general-owner@postgresql.org  Thu Sep 26 05:46:29 2002
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From: "Shridhar Daithankar" <shridhar_daithankar@persistent.co.in>
To: pgsql-hackers@postgresql.org, pgsql-general@postgresql.org
Date: Thu, 26 Sep 2002 15:16:50 +0530
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Subject: Re: Performance while loading data and indexing
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On 26 Sep 2002 at 19:05, Martijn van Oosterhout wrote:

> On Thu, Sep 26, 2002 at 02:05:44PM +0530, Shridhar Daithankar wrote:
> > 1) Database load time from flat file using copy is very high
> > 2) Creating index takes huge amount of time.
> > 3) Any suggsestions for runtime as data load and query will be going in 
> > parallel.
> 
> You're loading all the data in one copy. I find that INSERTs are mostly
> limited by indexes. While index lookups are cheap, they are not free and
> each index needs to be updated for each row.
> 
> I fond using partial indexes to only index the rows you actually use can
> help with the loading. It's a bit obscure though.
> 
> As for parallel loading, you'll be limited mostly by your I/O bandwidth.
> Have you measured it to take sure it's up to speed?

Well. It's like this, as of now.. CreateDB->create table->create index->Select.

So loading is not slowed by index. As of your hint of vmstat, will check it 
out.
> So you're loading at a rate of 860KB per sec. That's not too fast. How many
> indexes are active at that time? Triggers and foreign keys also take their
> toll.

Nothing except the table where data os  loaded..

> fsync IIRC only affects the WAL buffers now but it may be quite expensive,
> especially considering it's running on every transaction commit. Oh, your
> WAL files are on a seperate disk from the data?

No. Same RAID 5 disks..

> It shouldn't. Do you have an idea of what your CPU usage is? ps aux should
> give you a decent idea.

I guess we forgot to monitor system parameters. Next on my list is running 
vmstat, top and tuning bdflush.
 
> Find the bottleneck: CPU, I/O or memory?

Understood..
> 
> > Mysql is almost out because it's creating index for last 17 hours. I don't 
> > think it will keep up with 5K inserts per sec. with index. SAP DB is under 
> > evaluation too. But postgresql is most favourite as of now because it works. So 
> > I need to come up with solutions to problems that will occur in near future..
> > ;-)
> 
> 17 hours! Ouch. Either way, you should be able to do much better. Hope this
> helps,

Heh.. no wonder this evaluation is taking more than 2 weeks.. Mysql was running 
out of disk space while creating index and crashin. An upgrade to mysql helped 
there but no numbers as yet..

Thanks once again...
Bye
 Shridhar

--
Boren's Laws:	(1) When in charge, ponder.	(2) When in trouble, delegate.	(3) 
When in doubt, mumble.


From pgsql-general-owner@postgresql.org  Thu Sep 26 05:59:51 2002
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On Thursday 26 Sep 2002 9:35 am, Shridhar Daithankar wrote:

[questions re: large database]

Before reading my advice please bear in mind you are operating way beyond t=
he=20
scale of anything I have ever built.

> Now the details. Note that this is a test run only..
>
> Platform:- 4x Xeon2.4GHz/4GB RAM/4x48 SCSI RAID5/72 GB SCSI
> RedHat7.2/PostgreSQL7.1.3
>
> Database in flat file:
> 125,000,000 records of around 100 bytes each.
> Flat file size 12GB
>
> Load time: 14581 sec/~8600 rows persec/~ an MB of data per sec.
> Create unique composite index on 2 char and a timestamp field:  25226 sec.
> Database size on disk: 26GB
> Select query: 1.5 sec. for approx. 150 rows.
>
> Important postgresql.conf settings
[snipped setting details for moment]

Have you tried putting the wal files, syslog etc on separate disks/volumes?=
 If=20
you've settled on Intel, about the only thing you can optimise further is t=
he=20
disks.

Oh - and the OS - make sure you're running a (good) recent kernel for that=
=20
sort of hardware, I seem to remember some substantial changes in the 2.4=20
series regarding multi-processor.

> Now the requirements
>
> Initial flat data load: 250GB of data. This has gone up since last query.
> It was 150GB earlier..
> Ongoing inserts: 5000/sec.
> Number of queries: 4800 queries/hour
> Query response time: 10 sec.

Is this 5000 rows in say 500 transactions or 5000 insert transactions per=
=20
second. How many concurrent clients is this? Similarly for the 4800 queries=
,=20
how many concurrent clients is this? Are they expected to return approx 150=
=20
rows as in your test?

> Now questions.
>
> 1)  Instead of copying from a single 12GB data file,  will a parallel copy
> from say 5 files will speed up the things?

If the CPU is the bottle-neck then it should, but it's difficult to say=20
without figures.

> Couple MB of data per sec. to disk is just not saturating it. It's a RAID=
 5
> setup..

What is saturating during the flat-file load? Something must be maxed in to=
p /=20
iostat / vmstat.

[snip]
>
> 5)Will upgrading to 7.2.2/7.3 beta help?

It's unlikely to hurt.

> All in all, in the  test, we didn't see the performance where hardware is
> saturated to it's limits.

Something *must* be.

What are your disaster recovery plans? I can see problems with taking backu=
ps=20
if this beast is live 24/7.

- Richard Huxton

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Date: Thu, 26 Sep 2002 19:49:53 +1000
From: Justin Clift <justin@postgresql.org>
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Subject: Re: [HACKERS] Performance while loading data and indexing
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Shridhar Daithankar wrote:
<snip>
> > > fsync=true (Sad but true. Left untouched.. Will that make a difference on
> > > SCSI?)
> >
> > Definitely.  Have directly measured a ~ 2x tps throughput increase on
> > FreeBSD when leaving fsync off whilst performance measuring stuff
> > recently (PG 7.2.2).  Like anything it'll depend on workload, phase of
> > moon, etc, but it's a decent indicator.
> 
> I didn't know even that matters with SCSI..Will check out..

Cool.  When testing it had FreeBSD 4.6.2 installed on one drive along
with the PostgreSQL 7.2.2 binaries, it had the data on a second drive
(mounted as /pgdata), and it had the pg_xlog directory mounted on a
third drive.  Swap had it's own drive as well.

Everything is UltraSCSI, etc.  Haven't yet tested for a performance
difference through moving the indexes to another drive after creation
though.  That apparently has the potential to help as well.

:-)

Regards and best wishes,

Justin Clift

-- 
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
   - Indira Gandhi

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Shridhar Daithankar wrote:
> 
> On 26 Sep 2002 at 19:05, Martijn van Oosterhout wrote:
<snip>
> > fsync IIRC only affects the WAL buffers now but it may be quite expensive,
> > especially considering it's running on every transaction commit. Oh, your
> > WAL files are on a seperate disk from the data?
> 
> No. Same RAID 5 disks..

Not sure if this is a good idea.  Would have to think deeply about the
controller and drive optimisation/load characteristics.

If it's any help, when I was testing recently with WAL on a separate
drive, the WAL logs were doing more read&writes per second than the main
data drive.  This would of course be affected by the queries you are
running against the database.  I was just running Tatsuo's TPC-B stuff,
and the OSDB AS3AP tests.

> I guess we forgot to monitor system parameters. Next on my list is running
> vmstat, top and tuning bdflush.

That'll just be the start of it for serious performance tuning and
learning how PostgreSQL works.  :)

<snip>
> Thanks once again...
> Bye
>  Shridhar

-- 
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
   - Indira Gandhi

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Subject: Re: Performance while loading data and indexing 
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	<shridhar_daithankar@persistent.co.in>
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Date: Thu, 26 Sep 2002 10:33:58 -0400
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"Shridhar Daithankar" <shridhar_daithankar@persistent.co.in> writes:
> RedHat7.2/PostgreSQL7.1.3

I'd suggest a newer release of Postgres ... 7.1.3 is pretty old ...

> Create unique composite index on 2 char and a timestamp field:  25226 sec.

What do you mean by "char" exactly?  If it's really char(N), how much
are you paying in padding space?  There are very very few cases where
I'd not say to use varchar(N), or text, instead.  Also, does it have to
be character data?  If you could use an integer or float datatype
instead the index operations should be faster (though I can't say by
how much).  Have you thought carefully about the order in which the
composite index columns are listed?

> sort_mem = 12000

To create an index of this size, you want to push sort_mem as high as it
can go without swapping.  12000 sounds fine for the global setting, but
in the process that will create the index, try setting sort_mem to some
hundreds of megs or even 1Gb.  (But be careful: the calculation of space
actually used by CREATE INDEX is off quite a bit in pre-7.3 releases
:-(.  You should probably expect the actual process size to grow to two
or three times what you set sort_mem to.  Don't let it get so big as to
swap.)

> wal_buffers = 65536 

The above is a complete waste of memory space, which would be better
spent on letting the kernel expand its disk cache.  There's no reason
for wal_buffers to be more than a few dozen.

			regards, tom lane

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To: Justin Clift <justin@postgresql.org>
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Subject: Re: [HACKERS] Performance while loading data and indexing 
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	message dated "Thu, 26 Sep 2002 19:56:34 +1000"
Date: Thu, 26 Sep 2002 10:42:08 -0400
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Justin Clift <justin@postgresql.org> writes:
>> On 26 Sep 2002 at 19:05, Martijn van Oosterhout wrote:
>>> fsync IIRC only affects the WAL buffers now but it may be quite expensive,
>>> especially considering it's running on every transaction commit. Oh, your
>>> WAL files are on a seperate disk from the data?

> Not sure if this is a good idea.  Would have to think deeply about the
> controller and drive optimisation/load characteristics.

> If it's any help, when I was testing recently with WAL on a separate
> drive, the WAL logs were doing more read&writes per second than the main
> data drive.

... but way fewer seeks.  For anything involving lots of updating
transactions (and certainly 5000 separate insertions per second would
qualify; can those be batched??), it should be a win to put WAL on its
own spindle, just to get locality of access to the WAL.

			regards, tom lane

From pgsql-general-owner@postgresql.org  Thu Sep 26 10:51:34 2002
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From: "Shridhar Daithankar" <shridhar_daithankar@persistent.co.in>
To: pgsql-hackers@postgresql.org, pgsql-general@postgresql.org
Date: Thu, 26 Sep 2002 20:22:05 +0530
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Subject: Re: Performance while loading data and indexing 
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On 26 Sep 2002 at 10:33, Tom Lane wrote:

> "Shridhar Daithankar" <shridhar_daithankar@persistent.co.in> writes:
> > RedHat7.2/PostgreSQL7.1.3
> 
> I'd suggest a newer release of Postgres ... 7.1.3 is pretty old ...

I agree.. downloadind 7.2.2 right away..

> > Create unique composite index on 2 char and a timestamp field:  25226 sec.
> 
> What do you mean by "char" exactly?  If it's really char(N), how much
> are you paying in padding space?  There are very very few cases where
> I'd not say to use varchar(N), or text, instead.  Also, does it have to
> be character data?  If you could use an integer or float datatype
> instead the index operations should be faster (though I can't say by
> how much).  Have you thought carefully about the order in which the
> composite index columns are listed?

I have forwarded the idea of putting things into number. If it causes speedup 
in index lookup/creation, it would do. Looks like bigint is the order of the 
day..

> 
> > sort_mem = 12000
> 
> To create an index of this size, you want to push sort_mem as high as it
> can go without swapping.  12000 sounds fine for the global setting, but
> in the process that will create the index, try setting sort_mem to some
> hundreds of megs or even 1Gb.  (But be careful: the calculation of space
> actually used by CREATE INDEX is off quite a bit in pre-7.3 releases
> :-(.  You should probably expect the actual process size to grow to two
> or three times what you set sort_mem to.  Don't let it get so big as to
> swap.)

Great. I was skeptical to push it beyond 100MB. Now I can push it to corners..

> > wal_buffers = 65536 
> 
> The above is a complete waste of memory space, which would be better
> spent on letting the kernel expand its disk cache.  There's no reason
> for wal_buffers to be more than a few dozen.

That was a rather desparate move. Nothing was improving performance and then we 
started pushing numbers.. WIll get it back..  Same goes for 64 WAL files.. A GB 
looks like waste to me..

I might have found the bottleneck, although by accident. Mysql was running out 
of space while creating index. So my friend shut down mysql and tried to move 
things by hand to create links. He noticed that even things like cp were 
terribly slow and it hit us.. May be the culprit is the file system. Ext3 in 
this case. 

My friend argues for ext2 to eliminate journalling overhead but I favour 
reiserfs personally having used it in pgbench with 10M rows on paltry 20GB IDE 
disk for 25 tps..

We will be attempting raiserfs and/or XFS if required. I know how much speed 
difference exists between resiserfs and ext2. Would not be surprised if 
everythng just starts screaming in one go..

Bye
 Shridhar

--
Cropp's Law:	The amount of work done varies inversly with the time spent in the	
office.


From pgsql-general-owner@postgresql.org  Thu Sep 26 10:57:42 2002
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From: "Shridhar Daithankar" <shridhar_daithankar@persistent.co.in>
To: pgsql-hackers@postgresql.org, pgsql-general@postgresql.org
Date: Thu, 26 Sep 2002 20:28:11 +0530
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Subject: Re: [HACKERS] Performance while loading data and indexing 
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On 26 Sep 2002 at 10:42, Tom Lane wrote:

> Justin Clift <justin@postgresql.org> writes:
> > If it's any help, when I was testing recently with WAL on a separate
> > drive, the WAL logs were doing more read&writes per second than the main
> > data drive.
> 
> ... but way fewer seeks.  For anything involving lots of updating
> transactions (and certainly 5000 separate insertions per second would
> qualify; can those be batched??), it should be a win to put WAL on its
> own spindle, just to get locality of access to the WAL.

Probably they will be a single transcation. If possible we will bunch more of 
them together.. like 5 seconds of data pushed down in a single transaction but 
not sure it's possible..

This is bit like replication but from live oracle machine to postgres, from 
information I have. So there should be some chance of tuning there..

Bye
 Shridhar

--
Langsam's Laws:	(1) Everything depends.	(2) Nothing is always.	(3) Everything 
is sometimes.


From pgsql-general-owner@postgresql.org  Thu Sep 26 11:07:07 2002
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Organization: AcademSoft Ltd.
To: shridhar_daithankar@persistent.co.in,
	pgsql-hackers@postgresql.org, pgsql-general@postgresql.org
Subject: Re: [HACKERS] Performance while loading data and indexing
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On Thursday 26 September 2002 21:52, Shridhar Daithankar wrote:

> I might have found the bottleneck, although by accident. Mysql was running
> out of space while creating index. So my friend shut down mysql and tried
> to move things by hand to create links. He noticed that even things like cp
> were terribly slow and it hit us.. May be the culprit is the file system.
> Ext3 in this case.
>
> My friend argues for ext2 to eliminate journalling overhead but I favour
> reiserfs personally having used it in pgbench with 10M rows on paltry 20GB
> IDE disk for 25 tps..
>
> We will be attempting raiserfs and/or XFS if required. I know how much
> speed difference exists between resiserfs and ext2. Would not be surprised
> if everythng just starts screaming in one go..

As it was found by someone before any non-journaling FS is faster than
journaling one. This due to double work done by FS and database.

Try it on ext2 and compare.

--
Denis


From pgsql-general-owner@postgresql.org  Thu Sep 26 11:12:48 2002
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Shridhar Daithankar wrote:
<snip>
> My friend argues for ext2 to eliminate journalling overhead but I favour
> reiserfs personally having used it in pgbench with 10M rows on paltry 20GB IDE
> disk for 25 tps..

If it's any help, the setup I mentioned before with differnt disks for
the data and the WAL files was getting an average of about 72 tps with
200 concurrent users on pgbench.  Haven't tuned it in a hard core way at
all, and it only has 256MB DDR RAM in it at the moment (single CPU
AthonXP 1600).  These are figures made during the 2.5k+ test runs of
pgbench done when developing pg_autotune recently.

As a curiosity point, how predictable are the queries you're going to be
running on your database?  They sound very simple and very predicatable.

The pg_autotune tool might be your friend here.  It can deal with
arbitrary SQL instead of using the pg_bench stuff of Tatsuos, and it can
also deal with an already loaded database.  You'd just have to tweak the
names of the tables that it vacuums and the names of the indexes that it
reindexes between each run, to get some idea of your overall server
performance at different load points.

Probably worth taking a good look at if you're not afraid of editing
variables in C code.  :)
 
> We will be attempting raiserfs and/or XFS if required. I know how much speed
> difference exists between resiserfs and ext2. Would not be surprised if
> everythng just starts screaming in one go..

We'd all probably be interested to hear this.  Added the PostgreSQL
"Performance" mailing list to this thread too, Just In Case. (wow that's
a lot of cross posting now).

Regards and best wishes,

Justin Clift
 
> Bye
>  Shridhar
> 
> --
> Cropp's Law:    The amount of work done varies inversly with the time spent in the
> office.
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 3: if posting/reading through Usenet, please send an appropriate
> subscribe-nomail command to majordomo@postgresql.org so that your
> message can get through to the mailing list cleanly

-- 
"My grandfather once told me that there are two kinds of people: those
who work and those who take the credit. He told me to try to be in the
first group; there was less competition there."
   - Indira Gandhi

From pgsql-general-owner@postgresql.org  Thu Sep 26 11:28:32 2002
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Date: Thu, 26 Sep 2002 20:59:01 +0530
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Subject: Re: Performance while loading data and indexing
Reply-To: shridhar_daithankar@persistent.co.in
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	PostgreSQL General Mailing List <pgsql-general@postgresql.org>
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On 27 Sep 2002 at 1:12, Justin Clift wrote:

> Shridhar Daithankar wrote:
> As a curiosity point, how predictable are the queries you're going to be
> running on your database?  They sound very simple and very predicatable.

Mostly predictable selects. Not a domain expert on telecom so not very sure. 
But in my guess prepare statement in 7.3 should come pretty handy. i.e. by the 
time we finish evaluation and test deployment, 7.3 will be out in next couple 
of months to say so. So I would recommend doing it 7.3 way only..
> 
> The pg_autotune tool might be your friend here.  It can deal with
> arbitrary SQL instead of using the pg_bench stuff of Tatsuos, and it can
> also deal with an already loaded database.  You'd just have to tweak the
> names of the tables that it vacuums and the names of the indexes that it
> reindexes between each run, to get some idea of your overall server
> performance at different load points.
> 
> Probably worth taking a good look at if you're not afraid of editing
> variables in C code.  :)

Gladly. We started with altering pgbench here for testing and rapidly settled 
to perl generated random queries. Once postgresql wins the evaluation match and 
things come to implementation, pg_autotune would be a handy tool. Just that 
can't do it right now. Have to fight mysql and SAP DB before that..

BTW any performance figures on SAP DB? People here are as it frustrated with it 
with difficulties in setting it up. But still..
>  

> > We will be attempting raiserfs and/or XFS if required. I know how much speed
> > difference exists between resiserfs and ext2. Would not be surprised if
> > everythng just starts screaming in one go..
> 
> We'd all probably be interested to hear this.  Added the PostgreSQL
> "Performance" mailing list to this thread too, Just In Case. (wow that's
> a lot of cross posting now).

I know..;-) Glad that PG list does not have strict policies like no non-
subscriber posting or no attachments.. etc.. 

IMO reiserfs, though journalling one, is faster than ext2 etc. because the way 
it handles metadata. Personally I haven't come across ext2 being faster than 
reiserfs on few machine here for day to day use.

I guess I should have a freeBSD CD handy too.. Just to give it a try. If it 
comes down to a better VM.. though using 2.4.19 here.. so souldn't matter 
much..

I will keep you guys posted on file system stuff... Glad that we have much 
flexibility with postgresql..

Bye
 Shridhar

--
Bilbo's First Law:	You cannot count friends that are all packed up in barrels.


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Subject: Re: [HACKERS] Performance while loading data and indexing
From: Greg Copeland <greg@CopelandConsulting.Net>
To: shridhar_daithankar@persistent.co.in
Cc: PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
	PostgresSQL General Mailing List <pgsql-general@postgresql.org>
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On Thu, 2002-09-26 at 09:52, Shridhar Daithankar wrote:
> My friend argues for ext2 to eliminate journalling overhead but I favour=
=20
> reiserfs personally having used it in pgbench with 10M rows on paltry 20G=
B IDE=20
> disk for 25 tps..
>=20
> We will be attempting raiserfs and/or XFS if required. I know how much sp=
eed=20
> difference exists between resiserfs and ext2. Would not be surprised if=
=20
> everythng just starts screaming in one go..
>=20

I'm not sure about reiserfs or ext3 but with XFS, you can create your
log on another disk.  Also worth noting is that you can also configure
the size and number of log buffers.  There are also some other
performance type enhancements you can fiddle with if you don't mind
risking time stamp consistency in the event of a crash.  If your setup
allows for it, you might want to consider using XFS in this
configuration.

While I have not personally tried moving XFS' log to another device,
I've heard that performance gains can be truly stellar.  Assuming memory
allows, twiddling with the log buffering is said to allow for large
strides in performance as well.

If you do try this, I'd love to hear back about your results and
impressions.

Greg


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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200209261641.g8QGfYc04099@candle.pha.pa.us>
Subject: Re: Performance while loading data and indexing
In-Reply-To: <3D936C6D.12380.14936AEC@localhost>
To: shridhar_daithankar@persistent.co.in
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Shridhar Daithankar wrote:
> I might have found the bottleneck, although by accident. Mysql was running out 
> of space while creating index. So my friend shut down mysql and tried to move 
> things by hand to create links. He noticed that even things like cp were 
> terribly slow and it hit us.. May be the culprit is the file system. Ext3 in 
> this case. 

I just added a file system and multi-cpu section to my performance
tuning paper:

	http://www.ca.postgresql.org/docs/momjian/hw_performance/

The paper does recommend ext3, but the differences between file systems
are very small. If you are seeing 'cp' as slow, I wonder if it may be
something more general, like poorly tuned hardware or something. You can
use 'dd' to throw some data around the file system and see if that is
showing slowness;  compare those numbers to another machine that has
different hardware/OS.

Also, though ext3 is slower, turning fsync off should make ext3 function
similar to ext2.  That would be an interesting test if you suspect ext3.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

From pgsql-general-owner@postgresql.org  Thu Sep 26 13:17:12 2002
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From: Doug cNaught <doug@wireboard.com>
Cc: shridhar_daithankar@persistent.co.in,
	PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
	PostgresSQL General Mailing List <pgsql-general@postgresql.org>
Subject: Re: [HACKERS] Performance while loading data and indexing
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Greg Copeland <greg@CopelandConsulting.Net> writes:

> I'm not sure about reiserfs or ext3 but with XFS, you can create your
> log on another disk.  Also worth noting is that you can also configure
> the size and number of log buffers.  There are also some other
> performance type enhancements you can fiddle with if you don't mind
> risking time stamp consistency in the event of a crash.  If your setup
> allows for it, you might want to consider using XFS in this
> configuration.

You can definitely put the ext3 log on a different disk with 2.4
kernels.  

Also, if you put the WAL logs on a different disk from the main
database, and mount that partition with 'data=writeback' (ie
metadata-only journaling) ext3 should be pretty fast, since WAL files
are preallocated and there will therefore be almost no metadata
updates.

You should be able to mount the main database with "data=ordered" (the
default) for good performance and reasonable safety.

I think putting WAL on its own disk(s) is one of the keys here.

-Doug

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Subject: Re: [HACKERS] Performance while loading data and indexing
From: Greg Copeland <greg@CopelandConsulting.Net>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: shridhar_daithankar@persistent.co.in,
	PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
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On Thu, 2002-09-26 at 11:41, Bruce Momjian wrote:
> Shridhar Daithankar wrote:
> > I might have found the bottleneck, although by accident. Mysql was runn=
ing out=20
> > of space while creating index. So my friend shut down mysql and tried t=
o move=20
> > things by hand to create links. He noticed that even things like cp wer=
e=20
> > terribly slow and it hit us.. May be the culprit is the file system. Ex=
t3 in=20
> > this case.=20
>=20
> I just added a file system and multi-cpu section to my performance
> tuning paper:
>=20
> 	http://www.ca.postgresql.org/docs/momjian/hw_performance/
>=20
> The paper does recommend ext3, but the differences between file systems
> are very small. If you are seeing 'cp' as slow, I wonder if it may be
> something more general, like poorly tuned hardware or something. You can
> use 'dd' to throw some data around the file system and see if that is
> showing slowness;  compare those numbers to another machine that has
> different hardware/OS.


That's a good point.  Also, if you're using IDE, you do need to verify
that you're using DMA and proper PIO mode if at possible.  Also, big
performance improvements can be seen by making sure your IDE bus speed
has been properly configured.  The drivetweak-gtk and hdparm utilities
can make huge difference in performance.  Just be sure you know what the
heck your doing when you mess with those.

Greg


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Subject: Re: [HACKERS] Performance while loading data and indexing
From: Greg Copeland <greg@CopelandConsulting.Net>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: shridhar_daithankar@persistent.co.in,
	PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
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On Thu, 2002-09-26 at 11:41, Bruce Momjian wrote:
> Shridhar Daithankar wrote:
> > I might have found the bottleneck, although by accident. Mysql was runn=
ing out=20
> > of space while creating index. So my friend shut down mysql and tried t=
o move=20
> > things by hand to create links. He noticed that even things like cp wer=
e=20
> > terribly slow and it hit us.. May be the culprit is the file system. Ex=
t3 in=20
> > this case.=20
>=20
> I just added a file system and multi-cpu section to my performance
> tuning paper:
>=20
> 	http://www.ca.postgresql.org/docs/momjian/hw_performance/
>=20
> The paper does recommend ext3, but the differences between file systems
> are very small. If you are seeing 'cp' as slow, I wonder if it may be
> something more general, like poorly tuned hardware or something. You can
> use 'dd' to throw some data around the file system and see if that is
> showing slowness;  compare those numbers to another machine that has
> different hardware/OS.
>=20
> Also, though ext3 is slower, turning fsync off should make ext3 function
> similar to ext2.  That would be an interesting test if you suspect ext3.

I'm curious as to why you recommended ext3 versus some other (JFS,
XFS).  Do you have tests which validate that recommendation or was it a
simple matter of getting the warm fuzzies from familiarity?

Greg


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From pgsql-general-owner@postgresql.org  Thu Sep 26 14:46:12 2002
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Date: Thu, 26 Sep 2002 12:41:55 -0600 (MDT)
From: "scott.marlowe" <scott.marlowe@ihs.com>
To: Shridhar Daithankar <shridhar_daithankar@persistent.co.in>
Cc: <pgsql-hackers@postgresql.org>, <pgsql-general@postgresql.org>
Subject: Re: [HACKERS] Performance while loading data and indexing
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If you are seeing very slow performance on a drive set, check dmesg to see 
if you're getting SCSI bus errors or something similar.  If your drives 
aren't properly terminated then the performance will suffer a great deal.


From pgsql-general-owner@postgresql.org  Thu Sep 26 16:01:20 2002
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From: Bruce Momjian <pgman@candle.pha.pa.us>
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Subject: Re: [HACKERS] Performance while loading data and indexing
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To: Greg Copeland <greg@copelandconsulting.net>
Date: Thu, 26 Sep 2002 16:00:48 -0400 (EDT)
Cc: shridhar_daithankar@persistent.co.in,
	PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
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Greg Copeland wrote:
> > The paper does recommend ext3, but the differences between file systems
> > are very small. If you are seeing 'cp' as slow, I wonder if it may be
> > something more general, like poorly tuned hardware or something. You can
> > use 'dd' to throw some data around the file system and see if that is
> > showing slowness;  compare those numbers to another machine that has
> > different hardware/OS.
> > 
> > Also, though ext3 is slower, turning fsync off should make ext3 function
> > similar to ext2.  That would be an interesting test if you suspect ext3.
> 
> I'm curious as to why you recommended ext3 versus some other (JFS,
> XFS).  Do you have tests which validate that recommendation or was it a
> simple matter of getting the warm fuzzies from familiarity?

I used the attached email as a reference.  I just changed the wording to
be:
	
	File system choice is particularly difficult on Linux because there are
	so many file system choices, and none of them are optimal: ext2 is not
	entirely crash-safe, ext3 and xfs are journal-based, and Reiser is
	optimized for small files. Fortunately, the journaling file systems
	aren't significantly slower than ext2 so they are probably the best
	choice.

so I don't specifically recommend ext3 anymore.  As I remember, ext3 is
good only in that it can read ext2 file systems.  I think XFS may be the
best bet.

Can anyone clarify if "data=writeback" is safe for PostgreSQL. 
Specifically, are the data files recovered properly or is this option
only for a filesystem containing WAL?

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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	pgsql-hackers@postgresql.org, pgsql-general@postgresql.org
Subject: Re: [HACKERS] Performance while loading data and indexing
References: <200209261641.g8QGfYc04099@candle.pha.pa.us>
From: Neil Conway <neilc@samurai.com>
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Bruce Momjian <pgman@candle.pha.pa.us> writes:
> The paper does recommend ext3, but the differences between file systems
> are very small.

Well, I only did a very rough benchmark (a few runs of pgbench), but
the results I found were drastically different: ext2 was significantly
faster (~50%) than ext3-writeback, which was in turn significantly
faster (~25%) than ext3-ordered.

> Also, though ext3 is slower, turning fsync off should make ext3 function
> similar to ext2.

Why would that be?

Cheers,

Neil

-- 
Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC


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Subject: Re: [HACKERS] Performance while loading data and indexing
In-Reply-To: <871y7g1o1e.fsf@mailbox.samurai.com>
To: Neil Conway <neilc@samurai.com>
Date: Thu, 26 Sep 2002 16:45:54 -0400 (EDT)
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	pgsql-hackers@postgresql.org, pgsql-general@postgresql.org
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Neil Conway wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > The paper does recommend ext3, but the differences between file systems
> > are very small.
> 
> Well, I only did a very rough benchmark (a few runs of pgbench), but
> the results I found were drastically different: ext2 was significantly
> faster (~50%) than ext3-writeback, which was in turn significantly
> faster (~25%) than ext3-ordered.

Wow.  That leaves no good Linux file system alternatives.  PostgreSQL
just wants an ordinary file system that has reliable recovery from a
crash.

> > Also, though ext3 is slower, turning fsync off should make ext3 function
> > similar to ext2.
> 
> Why would that be?

I assumed it was the double fsync for the normal and journal that made
the journalling file systems slog.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

From pgsql-hackers-owner@postgresql.org  Thu Sep 26 16:50:43 2002
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To: Neil Conway <neilc@samurai.com>, pgsql-hackers@postgresql.org
Subject: Re: [GENERAL] Performance while loading data and indexing
References: <200209261641.g8QGfYc04099@candle.pha.pa.us>
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I have seen various benchmarks where XFS seems to perform best when it 
comes to huge amounts of data and many files (due to balanced internal 
b+ trees).
also, XFS seems to be VERY mature and very stable.
ext2/3 don't seem to be that fast in most of the benchmarks.

i did some testing with reiser some time ago. the problem is that it 
seems to restore a very historic consistent snapshot of the data. XFS 
seems to be much better in this respect.

i have not tested JFS yet (but on this damn AIX beside me)
from my point of view i strongly recommend XFS (maybe somebody from 
RedHat should think about it).

    Hans


Neil Conway wrote:

>Bruce Momjian <pgman@candle.pha.pa.us> writes:
>  
>
>>The paper does recommend ext3, but the differences between file systems
>>are very small.
>>    
>>
>
>Well, I only did a very rough benchmark (a few runs of pgbench), but
>the results I found were drastically different: ext2 was significantly
>faster (~50%) than ext3-writeback, which was in turn significantly
>faster (~25%) than ext3-ordered.
>
>  
>
>>Also, though ext3 is slower, turning fsync off should make ext3 function
>>similar to ext2.
>>    
>>
>
>Why would that be?
>
>Cheers,
>
>Neil
>
>  
>


-- 
*Cybertec Geschwinde u Schoenig*
Ludo-Hartmannplatz 1/14, A-1160 Vienna, Austria
Tel: +43/1/913 68 09; +43/664/233 90 75
www.postgresql.at <http://www.postgresql.at>, cluster.postgresql.at 
<http://cluster.postgresql.at>, www.cybertec.at 
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From pgsql-general-owner@postgresql.org  Thu Sep 26 16:57:22 2002
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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200209262057.g8QKv3Z22867@candle.pha.pa.us>
Subject: Re: [HACKERS] Performance while loading data and indexing
In-Reply-To: <871y7g1o1e.fsf@mailbox.samurai.com>
To: Neil Conway <neilc@samurai.com>
Date: Thu, 26 Sep 2002 16:57:03 -0400 (EDT)
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	pgsql-hackers@postgresql.org, pgsql-general@postgresql.org
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Neil Conway wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > The paper does recommend ext3, but the differences between file systems
> > are very small.
> 
> Well, I only did a very rough benchmark (a few runs of pgbench), but
> the results I found were drastically different: ext2 was significantly
> faster (~50%) than ext3-writeback, which was in turn significantly
> faster (~25%) than ext3-ordered.
> 
> > Also, though ext3 is slower, turning fsync off should make ext3 function
> > similar to ext2.
> 
> Why would that be?

OK, I changed the text to:
	
	File system choice is particularly difficult on Linux because there are
	so many file system choices, and none of them are optimal: ext2 is not
	entirely crash-safe, ext3, xfs, and jfs are journal-based, and Reiser is
	optimized for small files and does journalling. The journalling file
	systems can be significantly slower than ext2 but when crash recovery is
	required, ext2 isn't an option.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

From pgsql-general-owner@postgresql.org  Thu Sep 26 17:03:41 2002
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	shridhar_daithankar@persistent.co.in, pgsql-hackers@postgresql.org,
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Subject: Re: [HACKERS] Performance while loading data and indexing
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Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Wow.  That leaves no good Linux file system alternatives.
> PostgreSQL just wants an ordinary file system that has reliable
> recovery from a crash.

I'm not really familiar with the reasoning behind ext2's reputation as
recovering poorly from crashes; if we fsync a WAL record to disk
before we lose power, can't we recover reliably, even with ext2?

> > > Also, though ext3 is slower, turning fsync off should make ext3
> > > function similar to ext2.
> > 
> > Why would that be?
> 
> I assumed it was the double fsync for the normal and journal that
> made the journalling file systems slog.

Well, a journalling file system would need to write a journal entry
and flush that to disk, even if fsync is disabled -- whereas without
fsync enabled, ext2 doesn't have to flush anything to disk. ISTM that
the performance advantage of ext2 over ext3 is should be even larger
when fsync is not enabled.

Cheers,

Neil

-- 
Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC


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Subject: Re: [GENERAL] Performance while loading data and indexing
From: Greg Copeland <greg@CopelandConsulting.Net>
To: hs@cybertec.at
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I tend to agree with this though I have nothing to back up it with.  My
impression is that XFS does very well for large files.  Accepting that
as fact?, my impression is that XFS historically does well for
database's.  Again, I have nothing to back that up other than hear-say
and conjecture.

Greg


On Thu, 2002-09-26 at 15:55, Hans-J=FCrgen Sch=F6nig wrote:
> I have seen various benchmarks where XFS seems to perform best when it=20
> comes to huge amounts of data and many files (due to balanced internal=20
> b+ trees).
> also, XFS seems to be VERY mature and very stable.
> ext2/3 don't seem to be that fast in most of the benchmarks.
>=20
> i did some testing with reiser some time ago. the problem is that it=20
> seems to restore a very historic consistent snapshot of the data. XFS=20
> seems to be much better in this respect.
>=20
> i have not tested JFS yet (but on this damn AIX beside me)
> from my point of view i strongly recommend XFS (maybe somebody from=20
> RedHat should think about it).
>=20
>     Hans
>=20
>=20
> Neil Conway wrote:
>=20
> >Bruce Momjian <pgman@candle.pha.pa.us> writes:
> >=20=20
> >
> >>The paper does recommend ext3, but the differences between file systems
> >>are very small.
> >>=20=20=20=20
> >>
> >
> >Well, I only did a very rough benchmark (a few runs of pgbench), but
> >the results I found were drastically different: ext2 was significantly
> >faster (~50%) than ext3-writeback, which was in turn significantly
> >faster (~25%) than ext3-ordered.
> >
> >=20=20
> >
> >>Also, though ext3 is slower, turning fsync off should make ext3 function
> >>similar to ext2.
> >>=20=20=20=20
> >>
> >
> >Why would that be?
> >
> >Cheers,
> >
> >Neil
> >
> >=20=20
> >
>=20
>=20
> --=20
> *Cybertec Geschwinde u Schoenig*
> Ludo-Hartmannplatz 1/14, A-1160 Vienna, Austria
> Tel: +43/1/913 68 09; +43/664/233 90 75
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Subject: Re: [GENERAL] Performance while loading data and indexing
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Has there been any thought of providing RAW disk support to bypass the fs?

-----Original Message-----
From: pgsql-hackers-owner@postgresql.org
[mailto:pgsql-hackers-owner@postgresql.org]On Behalf Of Bruce Momjian
Sent: Thursday, September 26, 2002 3:57 PM
To: Neil Conway
Cc: shridhar_daithankar@persistent.co.in; pgsql-hackers@postgresql.org;
pgsql-general@postgresql.org
Subject: Re: [HACKERS] [GENERAL] Performance while loading data and
indexing


Neil Conway wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > The paper does recommend ext3, but the differences between file systems
> > are very small.
>
> Well, I only did a very rough benchmark (a few runs of pgbench), but
> the results I found were drastically different: ext2 was significantly
> faster (~50%) than ext3-writeback, which was in turn significantly
> faster (~25%) than ext3-ordered.
>
> > Also, though ext3 is slower, turning fsync off should make ext3 function
> > similar to ext2.
>
> Why would that be?

OK, I changed the text to:

	File system choice is particularly difficult on Linux because there are
	so many file system choices, and none of them are optimal: ext2 is not
	entirely crash-safe, ext3, xfs, and jfs are journal-based, and Reiser is
	optimized for small files and does journalling. The journalling file
	systems can be significantly slower than ext2 but when crash recovery is
	required, ext2 isn't an option.

--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200209262107.g8QL7vN25965@candle.pha.pa.us>
Subject: Re: [HACKERS] Performance while loading data and indexing
In-Reply-To: <87vg4szco1.fsf@mailbox.samurai.com>
To: Neil Conway <neilc@samurai.com>
Date: Thu, 26 Sep 2002 17:07:57 -0400 (EDT)
Cc: shridhar_daithankar@persistent.co.in,
	pgsql-hackers@postgresql.org, pgsql-general@postgresql.org
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Neil Conway wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Wow.  That leaves no good Linux file system alternatives.
> > PostgreSQL just wants an ordinary file system that has reliable
> > recovery from a crash.
> 
> I'm not really familiar with the reasoning behind ext2's reputation as
> recovering poorly from crashes; if we fsync a WAL record to disk
> before we lose power, can't we recover reliably, even with ext2?
> 
> > > > Also, though ext3 is slower, turning fsync off should make ext3
> > > > function similar to ext2.
> > > 
> > > Why would that be?
> > 
> > I assumed it was the double fsync for the normal and journal that
> > made the journalling file systems slog.
> 
> Well, a journalling file system would need to write a journal entry
> and flush that to disk, even if fsync is disabled -- whereas without
> fsync enabled, ext2 doesn't have to flush anything to disk. ISTM that
> the performance advantage of ext2 over ext3 is should be even larger
> when fsync is not enabled.

Yes, it is still double-writing.  I just thought that if that wasn't
happening while the db was waiting for a commit that it wouldn't be too
bad.

Is it just me or do all the Linux file systems seem like they are
lacking something when PostgreSQL is concerned?  We just want a UFS-like
file system on Linux and no one has it.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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Subject: Re: [HACKERS] Performance while loading data and indexing
From: Greg Copeland <greg@CopelandConsulting.Net>
To: Neil Conway <neilc@samurai.com>
Cc: Bruce Momjian <pgman@candle.pha.pa.us>,
	shridhar_daithankar@persistent.co.in,
	PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
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On Thu, 2002-09-26 at 16:03, Neil Conway wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Wow.  That leaves no good Linux file system alternatives.
> > PostgreSQL just wants an ordinary file system that has reliable
> > recovery from a crash.
>=20
> I'm not really familiar with the reasoning behind ext2's reputation as
> recovering poorly from crashes; if we fsync a WAL record to disk
> before we lose power, can't we recover reliably, even with ext2?

Well, I have experienced data loss from ext2 before.  Also, recovery
from crashes on large file systems take a very, very long time.  I can't
imagine anyone running a production database on an ext2 file system
having 10's or even 100's of GB.  Ouch.  Recovery would take forever!=20
Even recovery on small file systems (2-8G) can take extended periods of
time.  Especially so on IDE systems.  Even then manual intervention is
not uncommon.

While I can't say that x, y or z is the best FS to use on Linux, I can
say that ext2 is probably an exceptionally poor choice from a
reliability and/or uptime perspective.

Greg


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From pgsql-general-owner@postgresql.org  Thu Sep 26 17:17:43 2002
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To: Greg Copeland <greg@CopelandConsulting.Net>
Cc: Neil Conway <neilc@samurai.com>, Bruce Momjian <pgman@candle.pha.pa.us>,
	shridhar_daithankar@persistent.co.in,
	PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
	PostgresSQL General Mailing List <pgsql-general@postgresql.org>
Subject: Re: [HACKERS] Performance while loading data and indexing
References: <200209262045.g8QKjtv21744@candle.pha.pa.us>
	<87vg4szco1.fsf@mailbox.samurai.com>
	<1033074555.23344.48.camel@mouse.copelandconsulting.net>
From: Neil Conway <neilc@samurai.com>
In-Reply-To: <1033074555.23344.48.camel@mouse.copelandconsulting.net>
Date: 26 Sep 2002 17:17:30 -0400
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Greg Copeland <greg@CopelandConsulting.Net> writes:
> On Thu, 2002-09-26 at 16:03, Neil Conway wrote:
> > I'm not really familiar with the reasoning behind ext2's
> > reputation as recovering poorly from crashes; if we fsync a WAL
> > record to disk before we lose power, can't we recover reliably,
> > even with ext2?
> 
> Well, I have experienced data loss from ext2 before.  Also, recovery
> from crashes on large file systems take a very, very long time.

Yes, but wouldn't you face exactly the same issues if you ran a
UFS-like filesystem in asynchronous mode? Albeit it's not the default,
but performance in synchronous mode is usually pretty poor.

The fact that ext2 defaults to asynchronous mode and UFS (at least on
the BSDs) defaults to synchronous mode seems like a total non-issue to
me. Is there any more to the alleged difference in reliability?

Cheers,

Neil

-- 
Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC


From pgsql-general-owner@postgresql.org  Thu Sep 26 17:32:17 2002
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To: Bruce Momjian <pgman@candle.pha.pa.us>
From: Doug McNaught <doug@wireboard.com>
Cc: Greg Copeland <greg@copelandconsulting.net>,
	shridhar_daithankar@persistent.co.in,
	PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
	PostgresSQL General Mailing List <pgsql-general@postgresql.org>
Subject: Re: [HACKERS] Performance while loading data and indexing
References: <200209262000.g8QK0mG10553@candle.pha.pa.us>
Date: 26 Sep 2002 17:31:55 -0400
In-Reply-To: Bruce Momjian's message of "Thu,
 26 Sep 2002 16:00:48 -0400 (EDT)"
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Bruce Momjian <pgman@candle.pha.pa.us> writes:

> Can anyone clarify if "data=writeback" is safe for PostgreSQL. 
> Specifically, are the data files recovered properly or is this option
> only for a filesystem containing WAL?

"data=writeback" means that no data is journaled, just metadata (which
is like XFS or Reiser).  An fsync() call should still do what it
normally does, commit the writes to disk before returning.

"data=journal" journals all data and is the slowest and safest.
"data=ordered" writes out data blocks before committing a journal
transaction, which is faster than full data journaling (since data
doesn't get written twice) and almost as safe.  "data=writeback" is
noted to keep obsolete data in the case of some crashes (since the
data may not have been written yet) but a completed fsync() should
ensure that the data is valid.

So I guess I'd probably use data=ordered for an all-on-one-fs
installation, and data=writeback for a WAL-only drive.

Hope this helps...

-Doug

From pgsql-general-owner@postgresql.org  Thu Sep 26 17:32:39 2002
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To: Neil Conway <neilc@samurai.com>
Cc: Bruce Momjian <pgman@candle.pha.pa.us>,
	shridhar_daithankar@persistent.co.in, pgsql-hackers@postgresql.org,
	pgsql-general@postgresql.org
Subject: Re: [HACKERS] Performance while loading data and indexing 
In-reply-to: <87vg4szco1.fsf@mailbox.samurai.com> 
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	<87vg4szco1.fsf@mailbox.samurai.com>
Comments: In-reply-to Neil Conway <neilc@samurai.com>
	message dated "26 Sep 2002 17:03:26 -0400"
Date: Thu, 26 Sep 2002 17:32:01 -0400
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Neil Conway <neilc@samurai.com> writes:
> I'm not really familiar with the reasoning behind ext2's reputation as
> recovering poorly from crashes; if we fsync a WAL record to disk
> before we lose power, can't we recover reliably, even with ext2?

Up to a point.  We do assume that the filesystem won't lose checkpointed
(sync'd) writes to data files.  To the extent that the filesystem is
vulnerable to corruption of its own metadata for a file (indirect blocks
or whatever ext2 uses), that's not a completely safe assumption.

We'd be happiest with a filesystem that journals its own metadata and
not the user data in the file(s).  I dunno if there are any.

Hmm, maybe this is why Oracle likes doing their own filesystem on a raw
device...

			regards, tom lane

From pgsql-general-owner@postgresql.org  Thu Sep 26 17:37:39 2002
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To: Tom Lane <tgl@sss.pgh.pa.us>
From: Doug McNaught <doug@wireboard.com>
Cc: Neil Conway <neilc@samurai.com>, Bruce Momjian <pgman@candle.pha.pa.us>,
	shridhar_daithankar@persistent.co.in, pgsql-hackers@postgresql.org,
	pgsql-general@postgresql.org
Subject: Re: [HACKERS] Performance while loading data and indexing
References: <200209262045.g8QKjtv21744@candle.pha.pa.us>
	<87vg4szco1.fsf@mailbox.samurai.com> <12930.1033075921@sss.pgh.pa.us>
Date: 26 Sep 2002 17:37:10 -0400
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Tom Lane <tgl@sss.pgh.pa.us> writes:

> We'd be happiest with a filesystem that journals its own metadata and
> not the user data in the file(s).  I dunno if there are any.

ext3 with data=writeback?  (See my previous message to Bruce).

-Doug

From pgsql-general-owner@postgresql.org  Thu Sep 26 17:39:35 2002
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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200209262139.g8QLdEE08861@candle.pha.pa.us>
Subject: Re: [HACKERS] Performance while loading data and indexing
In-Reply-To: <87n0q4zc0l.fsf@mailbox.samurai.com>
To: Neil Conway <neilc@samurai.com>
Date: Thu, 26 Sep 2002 17:39:14 -0400 (EDT)
Cc: Greg Copeland <greg@CopelandConsulting.Net>,
	shridhar_daithankar@persistent.co.in,
	PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
	PostgresSQL General Mailing List <pgsql-general@postgresql.org>
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Neil Conway wrote:
> Greg Copeland <greg@CopelandConsulting.Net> writes:
> > On Thu, 2002-09-26 at 16:03, Neil Conway wrote:
> > > I'm not really familiar with the reasoning behind ext2's
> > > reputation as recovering poorly from crashes; if we fsync a WAL
> > > record to disk before we lose power, can't we recover reliably,
> > > even with ext2?
> > 
> > Well, I have experienced data loss from ext2 before.  Also, recovery
> > from crashes on large file systems take a very, very long time.
> 
> Yes, but wouldn't you face exactly the same issues if you ran a
> UFS-like filesystem in asynchronous mode? Albeit it's not the default,
> but performance in synchronous mode is usually pretty poor.

Yes, before UFS had soft updates, the synchronous nature of UFS made it
slower than ext2, but now with soft updates, that performance difference
is gone so you have two files systems, ext2 and ufs, similar peformance,
but one is crash-safe and the other is not.

And, when comparing the journalling file systems, you have UFS vs.
XFS/ext3/JFS/Reiser, and UFS is faster.  The only thing the journalling
file system give you is more rapid reboot, but frankly, if your OS goes
down often enough so that is an issue, you have bigger problems than
fsync time.

The big problem is that Linux went from non-crash safe right to
crash-safe and reboot quick.  We need a middle ground, which is where
UFS/soft updates is.

> The fact that ext2 defaults to asynchronous mode and UFS (at least on
> the BSDs) defaults to synchronous mode seems like a total non-issue to
> me. Is there any more to the alleged difference in reliability?

The reliability problem isn't alleged.  ext2 developers admits ext2
isn't 100% crash-safe.  They will say it is usually crash-safe, but that
isn't good enough for PostgreSQL.

I wish I was wrong.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

From pgsql-general-owner@postgresql.org  Thu Sep 26 17:42:05 2002
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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200209262141.g8QLfMr09064@candle.pha.pa.us>
Subject: Re: [HACKERS] Performance while loading data and indexing
In-Reply-To: <m3vg4sigah.fsf@varsoon.wireboard.com>
To: Doug McNaught <doug@wireboard.com>
Date: Thu, 26 Sep 2002 17:41:22 -0400 (EDT)
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Neil Conway <neilc@samurai.com>,
	shridhar_daithankar@persistent.co.in, pgsql-hackers@postgresql.org,
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Doug McNaught wrote:
> Tom Lane <tgl@sss.pgh.pa.us> writes:
> 
> > We'd be happiest with a filesystem that journals its own metadata and
> > not the user data in the file(s).  I dunno if there are any.
> 
> ext3 with data=writeback?  (See my previous message to Bruce).

OK, so that makes ext3 crash safe without lots of overhead?

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

From pgsql-hackers-owner@postgresql.org  Thu Sep 26 17:45:16 2002
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Subject: Re: [GENERAL] Performance while loading data and indexing
From: Rod Taylor <rbt@rbt.ca>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Neil Conway <neilc@samurai.com>,
	Greg Copeland <greg@CopelandConsulting.Net>,
	shridhar_daithankar@persistent.co.in,
	PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
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On Thu, 2002-09-26 at 17:39, Bruce Momjian wrote:
> Neil Conway wrote:
> > Greg Copeland <greg@CopelandConsulting.Net> writes:
> > > On Thu, 2002-09-26 at 16:03, Neil Conway wrote:
> > > > I'm not really familiar with the reasoning behind ext2's
> > > > reputation as recovering poorly from crashes; if we fsync a WAL
> > > > record to disk before we lose power, can't we recover reliably,
> > > > even with ext2?
> > > 
> > > Well, I have experienced data loss from ext2 before.  Also, recovery
> > > from crashes on large file systems take a very, very long time.
> > 
> > Yes, but wouldn't you face exactly the same issues if you ran a
> > UFS-like filesystem in asynchronous mode? Albeit it's not the default,
> > but performance in synchronous mode is usually pretty poor.
> 
> Yes, before UFS had soft updates, the synchronous nature of UFS made it
> slower than ext2, but now with soft updates, that performance difference
> is gone so you have two files systems, ext2 and ufs, similar peformance,
> but one is crash-safe and the other is not.

Note entirely true.  ufs is both crash-safe and quick-rebootable.  You
do need to fsck at some point, but not prior to mounting it.  Any
corrupt blocks are empty, and are easy to avoid.

Someone just needs to implement a background fsck that will run on a
mounted filesystem.

-- 
  Rod Taylor


From pgsql-general-owner@postgresql.org  Thu Sep 26 17:48:03 2002
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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200209262147.g8QLlhU10159@candle.pha.pa.us>
Subject: Re: [HACKERS] Performance while loading data and indexing
In-Reply-To: <1033076723.27772.4.camel@jester>
To: Rod Taylor <rbt@rbt.ca>
Date: Thu, 26 Sep 2002 17:47:43 -0400 (EDT)
Cc: Neil Conway <neilc@samurai.com>,
	Greg Copeland <greg@CopelandConsulting.Net>,
	shridhar_daithankar@persistent.co.in,
	PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
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Rod Taylor wrote:
> > Yes, before UFS had soft updates, the synchronous nature of UFS made it
> > slower than ext2, but now with soft updates, that performance difference
> > is gone so you have two files systems, ext2 and ufs, similar peformance,
> > but one is crash-safe and the other is not.
> 
> Note entirely true.  ufs is both crash-safe and quick-rebootable.  You
> do need to fsck at some point, but not prior to mounting it.  Any
> corrupt blocks are empty, and are easy to avoid.

I am assuming you need to mount the drive as part of the reboot.  Of
course you can boot fast with any file system if you don't have to mount
it.  :-)

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

From pgsql-general-owner@postgresql.org  Sat Sep 28 13:41:23 2002
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Subject: Re: [HACKERS] Performance while loading data and indexing
From: Rod Taylor <rbt@rbt.ca>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Neil Conway <neilc@samurai.com>,
	Greg Copeland <greg@CopelandConsulting.Net>,
	shridhar_daithankar@persistent.co.in,
	PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
	PostgresSQL General Mailing List <pgsql-general@postgresql.org>
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On Thu, 2002-09-26 at 17:47, Bruce Momjian wrote:
> Rod Taylor wrote:
> > > Yes, before UFS had soft updates, the synchronous nature of UFS made it
> > > slower than ext2, but now with soft updates, that performance difference
> > > is gone so you have two files systems, ext2 and ufs, similar peformance,
> > > but one is crash-safe and the other is not.
> > 
> > Note entirely true.  ufs is both crash-safe and quick-rebootable.  You
> > do need to fsck at some point, but not prior to mounting it.  Any
> > corrupt blocks are empty, and are easy to avoid.
> 
> I am assuming you need to mount the drive as part of the reboot.  Of
> course you can boot fast with any file system if you don't have to mount
> it.  :-)

Sorry, poor explanation.

Background fsck (when implemented) would operate on a currently mounted
(and active) file system.  The only reason fsck is required prior to
reboot now is because no-one had done the work.

http://www.freebsd.org/cgi/man.cgi?query=fsck&sektion=8&manpath=FreeBSD+5.0-current

See the first paragraph of the above.
-- 
  Rod Taylor


From pgsql-general-owner@postgresql.org  Thu Sep 26 18:05:13 2002
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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200209262204.g8QM4qX11641@candle.pha.pa.us>
Subject: Re: [HACKERS] Performance while loading data and indexing
In-Reply-To: <1033077816.27772.9.camel@jester>
To: Rod Taylor <rbt@rbt.ca>
Date: Thu, 26 Sep 2002 18:04:52 -0400 (EDT)
Cc: Neil Conway <neilc@samurai.com>,
	Greg Copeland <greg@CopelandConsulting.Net>,
	shridhar_daithankar@persistent.co.in,
	PostgresSQL Hackers Mailing List <pgsql-hackers@postgresql.org>,
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Rod Taylor wrote:
> On Thu, 2002-09-26 at 17:47, Bruce Momjian wrote:
> > Rod Taylor wrote:
> > > > Yes, before UFS had soft updates, the synchronous nature of UFS made it
> > > > slower than ext2, but now with soft updates, that performance difference
> > > > is gone so you have two files systems, ext2 and ufs, similar peformance,
> > > > but one is crash-safe and the other is not.
> > > 
> > > Note entirely true.  ufs is both crash-safe and quick-rebootable.  You
> > > do need to fsck at some point, but not prior to mounting it.  Any
> > > corrupt blocks are empty, and are easy to avoid.
> > 
> > I am assuming you need to mount the drive as part of the reboot.  Of
> > course you can boot fast with any file system if you don't have to mount
> > it.  :-)
> 
> Sorry, poor explanation.
> 
> Background fsck (when implemented) would operate on a currently mounted
> (and active) file system.  The only reason fsck is required prior to
> reboot now is because no-one had done the work.
> 
> http://www.freebsd.org/cgi/man.cgi?query=fsck&sektion=8&manpath=FreeBSD+5.0-current
> 
> See the first paragraph of the above.

Oh, yes, I have heard of that missing feature.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

From pgsql-general-owner@postgresql.org  Thu Sep 26 19:26:22 2002
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To: Bruce Momjian <pgman@candle.pha.pa.us>
From: Doug McNaught <doug@wireboard.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Neil Conway <neilc@samurai.com>,
	shridhar_daithankar@persistent.co.in, pgsql-hackers@postgresql.org,
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Subject: Re: [HACKERS] Performance while loading data and indexing
References: <200209262141.g8QLfMr09064@candle.pha.pa.us>
Date: 26 Sep 2002 19:26:03 -0400
In-Reply-To: Bruce Momjian's message of "Thu,
 26 Sep 2002 17:41:22 -0400 (EDT)"
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Bruce Momjian <pgman@candle.pha.pa.us> writes:

> Doug McNaught wrote:
> > Tom Lane <tgl@sss.pgh.pa.us> writes:
> > 
> > > We'd be happiest with a filesystem that journals its own metadata and
> > > not the user data in the file(s).  I dunno if there are any.
> > 
> > ext3 with data=writeback?  (See my previous message to Bruce).
> 
> OK, so that makes ext3 crash safe without lots of overhead?

Metadata is journaled so you shouldn't lose data blocks or directory
entries.  Some data blocks (that haven't been fsync()'ed) may have old
or wrong data in them, but I think that's the same as ufs, right?  And
WAL replay should take care of that.

It'd be very interesting to do some tests of the various journaling
modes.  I have an old K6 that I might be able to turn into a
hit-the-reset-switch-at-ramdom-times machine.  What kind of tests
should be run?

-Doug

From pgsql-performance-owner@postgresql.org  Thu Sep 26 22:53:21 2002
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Date: Fri, 27 Sep 2002 10:55:10 +0800
From: Yusuf Goolamabbas <yusufg@outblaze.com>
To: pgsql-performance@postgresql.org
Subject: Would ext3 data=journal help for Postgres synchronous io mode
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According to ext3 hackers (Stephen Tweedie, Andrew Morton). ext3
data=journal mode is much faster than any of the other mode for
workloads which do a lot of syncrhonous i/o. Personally, I have seen
dramatic improvements on moving mail queues to this mode (postfix in
particularly flies with this mode)

While this may seem contradictory (forcing journaling for the data in
addition to the metadata), it will likely improve the performance for
sync I/O loads like mail servers because it can do all of the I/O to the
journal without any seek or sync overhead while the mail is arriving.

I assume that since Postgresql does a lot of fsyncs, it would benefit
also. I have sent email to Sridhar asking if he could test this

Another thing to note is that Linux 2.4.x kernels < 2.4.20-pre4 use
bounce buffer's to do IO if the machine has > 1GB memory. Distributor
kernels such as Redhat/Suse/Mandrake are patched to do IO via DMA
to/from highmem (>1GB). According to IBM's paper @ OLS, this improves IO
performance by 40%

BTW, Is this list archived on the website

Regards, Yusuf
-- 
Yusuf Goolamabbas
yusufg@outblaze.com

From pgsql-general-owner@postgresql.org  Thu Sep 26 23:08:32 2002
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Subject: Re: [HACKERS] Performance while loading data and indexing 
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	<m3znu4igj8.fsf@varsoon.wireboard.com>
Comments: In-reply-to Doug McNaught <doug@wireboard.com>
	message dated "26 Sep 2002 17:31:55 -0400"
Date: Thu, 26 Sep 2002 23:07:44 -0400
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Doug McNaught <doug@wireboard.com> writes:
> "data=writeback" means that no data is journaled, just metadata (which
> is like XFS or Reiser).  An fsync() call should still do what it
> normally does, commit the writes to disk before returning.
> "data=journal" journals all data and is the slowest and safest.
> "data=ordered" writes out data blocks before committing a journal
> transaction, which is faster than full data journaling (since data
> doesn't get written twice) and almost as safe.  "data=writeback" is
> noted to keep obsolete data in the case of some crashes (since the
> data may not have been written yet) but a completed fsync() should
> ensure that the data is valid.

Thanks for the explanation.

> So I guess I'd probably use data=ordered for an all-on-one-fs
> installation, and data=writeback for a WAL-only drive.

Actually I think the ideal thing for Postgres would be data=writeback
for both data and WAL drives.  We can handle loss of un-fsync'd data
for ourselves in both cases.

Of course, if you keep anything besides Postgres data files on a
partition, you'd possibly want the more secure settings.

			regards, tom lane

From pgsql-general-owner@postgresql.org  Fri Sep 27 01:12:31 2002
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To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Neil Conway <neilc@samurai.com>, <shridhar_daithankar@persistent.co.in>,
	<pgsql-hackers@postgresql.org>, <pgsql-general@postgresql.org>
Subject: Re: [HACKERS] Performance while loading data and indexing
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Hello!

On Thu, 26 Sep 2002, Bruce Momjian wrote:

> > I'm not really familiar with the reasoning behind ext2's reputation as
> > recovering poorly from crashes; if we fsync a WAL record to disk

On relatively big volumes ext2 recovery can end up in formatting the fs 
under certain cirrumstances.;-)

> > > I assumed it was the double fsync for the normal and journal that
> > > made the journalling file systems slog.
> > 
> > Well, a journalling file system would need to write a journal entry
> > and flush that to disk, even if fsync is disabled -- whereas without
> > fsync enabled, ext2 doesn't have to flush anything to disk. ISTM that
> > the performance advantage of ext2 over ext3 is should be even larger
> > when fsync is not enabled.
> 
> Yes, it is still double-writing.  I just thought that if that wasn't
> happening while the db was waiting for a commit that it wouldn't be too
> bad.
> 
> Is it just me or do all the Linux file systems seem like they are
> lacking something when PostgreSQL is concerned?  We just want a UFS-like
> file system on Linux and no one has it.

mount -o sync an ext2 volume on Linux - and you can get a "UFS-like" fs.:)
mount -o async an FFS volume on FreeBSD  - and you can get boost in fs 
performance.
Personally me always mount ext2 fs where Pg is living with sync option.
Fsync in pg is off (since 6.3), this way successfully pass thru a few 
serious crashes on various systems (mostly on power problems).
If fsync is on in Pg, performance gets so-oh-oh-oh-oh slowly!=)
I just have done upgrade from 2.2 kernel on ext2 to ext3 capable 2.4 one
so I'm planning to do some benchmarking. Roughly saying w/o benchmarks, 
the performance have been degraded in 2/3 proportion.
"But better safe then sorry".

-- 
WBR, Yury Bokhoncovich, Senior System Administrator, NOC of F1 Group.
Phone: +7 (3832) 106228, ext.140, E-mail: byg@center-f1.ru.
Unix is like a wigwam -- no Gates, no Windows, and an Apache inside.



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From pgsql-general-owner@postgresql.org  Fri Sep 27 06:40:18 2002
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neilc@samurai.com (Neil Conway) writes:

[snip]
> > Well, I have experienced data loss from ext2 before.  Also, recovery
> > from crashes on large file systems take a very, very long time.
> 
> Yes, but wouldn't you face exactly the same issues if you ran a
> UFS-like filesystem in asynchronous mode? Albeit it's not the default,
> but performance in synchronous mode is usually pretty poor.
> 
> The fact that ext2 defaults to asynchronous mode and UFS (at least on
> the BSDs) defaults to synchronous mode seems like a total non-issue to
> me. Is there any more to the alleged difference in reliability?

UFS on most unix systems (BSD, solaris etc) defaults to sync
metadata, async data which is a mode that is completely missing
from ext2 as far as I know.

This is why UFS is considered safer than ext2. (Running with
'sync' is too slow to be a usable alternative in most cases.)

      _
Mats Lofkvist
mal@algonet.se


PS The BSD soft updates yields the safety of the default sync
   metadata / async data mode while being at least as fast as
   running fully async.

From pgsql-general-owner@postgresql.org  Fri Sep 27 06:49:23 2002
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From: Mats Lofkvist <mal@algonet.se>
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shridhar_daithankar@persistent.co.in ("Shridhar Daithankar") writes:

[snip]
> 
> Couple MB of data per sec. to disk is just not saturating it. It's a RAID 5 
> setup..
> 

RAID5 is not the best for performance, especially write performance.
If it is software RAID it is even worse :-).

(Note also that you need to check that you are not saturating the
number of seeks the disks can handle, not just the bandwith.)

Striping should be better (combined with mirroring if you need the
safety, but with both striping and mirroring you may need multiple
SCSI channels).

      _
Mats Lofkvist
mal@algonet.se

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From: "scott.marlowe" <scott.marlowe@ihs.com>
To: Mats Lofkvist <mal@algonet.se>
Cc: <pgsql-general@postgresql.org>
Subject: Re: Performance while loading data and indexing
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On 27 Sep 2002, Mats Lofkvist wrote:

> shridhar_daithankar@persistent.co.in ("Shridhar Daithankar") writes:
> 
> [snip]
> > 
> > Couple MB of data per sec. to disk is just not saturating it. It's a RAID 5 
> > setup..
> > 
> 
> RAID5 is not the best for performance, especially write performance.
> If it is software RAID it is even worse :-).

I take exception to this.  RAID5 is a great choice for most folks.

1:  RAID5 only writes out the parity stripe and data stripe, not all 
stripes when writing.  So, in an 8 disk RAID5 array, writing to a single 
64 k stripe involves one 64k read (parity stripe) and two 64k writes.

On a mirror set, writing to one 64k stripe involves two 64k writes.  The 
difference isn't that great, and in my testing, a large enough RAID5 
provides so much faster read speads by spreading the reads across so many 
heads as to more than make up for the slightly slower writes.  My testing 
has shown that a 4 disk RAID5 can generally run about 85% or more the 
speed of a mirror set.

2:  Why does EVERYONE have to jump on the bandwagon that software RAID 5 
is bad.  My workstation running RH 7.2 uses about 1% of the CPU during 
very heavy parallel access (i.e. 50 simo pgbenchs) at most.  I've seen 
many hardware RAID cards that are noticeable slower than my workstation 
running software RAID.  You do know that hardware RAID is just software 
RAID where the processing is done on a seperate CPU on a card, but it's 
still software doing the work.

3:  We just had a hardware RAID card mark both drives in a mirror set bad.  
It wouldn't accept them back, and all the data was gone.  poof.  That 
would never happen in Linux's kernel software RAID, I can always make 
Linux take back a "bad" drive.


The only difference between RAID5 with n+1 disks and RAID0 with n disks is 
that we have to write a parity stripe in RAID5.  It's ability to handle 
high parallel load is much better than a RAID1 set, and on average, you 
actually write about the same amount with either RAID1 or RAID5.

Don't dog software RAID5, it works and it works well in Linux.  Windows, 
however, is another issue.  There, the software RAID5 is pretty pitiful, 
both in terms of performance and maintenance.


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Subject: Re: [GENERAL] Performance while loading data and indexing
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Tom Lane <tgl@sss.pgh.pa.us> writes:

> We'd be happiest with a filesystem that journals its own metadata and
> not the user data in the file(s).  I dunno if there are any.

Most journalling file systems work this way.  Data journalling is not
very widespread, AFAIK.

-- 
Florian Weimer 	                  Weimer@CERT.Uni-Stuttgart.DE
University of Stuttgart           http://CERT.Uni-Stuttgart.DE/people/fw/
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scott.marlowe wrote:

>(snippage)
>I take exception to this.  RAID5 is a great choice for most folks.
>
>
I agree - certainly RAID5 *used* to be rather sad, but modern cards have 
improved this no end on the hardware side - e.g.

I recently benchmarked a 3Ware 8x card on a system with 4 x 15000 rpm 
Maxtor 70Gb drives and achieved 120 Mb/s for (8K) reads and 60 Mb/s for 
(8K) writes using RAID5. I used Redhat 7.3 +  ext2.  The benchmarking 
program was Bonnie.

Given that the performance of a single disk was ~30 Mb/s for reads and 
writes, I felt this was quite a good result ! ( Other cards I had tried 
previously struggled to maintain 1/2 the write rate of a single disk in 
such a configuration).

As for software RAID5, I have not tried it out.

Of course I could not get 60Mb/s while COPYing data into Postgres... 
typically cpu seemed to be the bottleneck in this case (what was the 
actual write rate? I hear you asking..err.. cant recall I'm afraid.. 
must try it out again )

cheers

Mark


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When a table is created with a primary key it generates a index.
Dos the queries on that table use that index automatically?
Do I need to reindex that index after insertions?

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<DIV><FONT face=3DArial size=3D2>When a table is created with a primary key=
 it=20
generates a index.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Dos the queries on that table use that ind=
ex=20
automatically?</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Do I need to reindex that index after=20
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From pgsql-performance-owner@postgresql.org  Sat Sep 28 15:13:19 2002
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From: Andrew Sullivan <andrew@libertyrms.info>
To: pgsql-performance@postgresql.org
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On Sat, Sep 28, 2002 at 09:50:13PM +0600, Waruna Geekiyanage wrote:
> When a table is created with a primary key it generates a index.
> Dos the queries on that table use that index automatically?

Only if you analyse the table, and it's a "win".  See the various
past discussion on -general, for instance, about index use, and the
FAQ.

> Do I need to reindex that index after insertions?

No, but you need to analyse.

A

-- 
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