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* Slow Postgresql server
@ 2007-04-11 22:02 Jason Lustig <lustig@brandeis.edu>
0 siblings, 3 replies; 13+ messages in thread
From: Jason Lustig @ 2007-04-11 22:02 UTC (permalink / raw)
To: pgsql-performance
Hello all,
My website has been having issues with our new Linux/PostgreSQL
server being somewhat slow. I have done tests using Apache Benchmark
and for pages that do not connect to Postgres, the speeds are much
faster (334 requests/second v. 1-2 requests/second), so it seems that
Postgres is what's causing the problem and not Apache. I did some
reserach, and it seems that the bottleneck is in fact the hard
drives! Here's an excerpt from vmstat:
procs -----------memory---------- ---swap-- -----io---- --system--
-----cpu------
r b swpd free buff cache si so bi bo in cs us
sy id wa st
1 1 140 24780 166636 575144 0 0 0 3900 1462 3299 1
4 49 48 0
0 1 140 24780 166636 575144 0 0 0 3828 1455 3391 0
4 48 48 0
1 1 140 24780 166636 575144 0 0 0 2440 960 2033 0
3 48 48 0
0 1 140 24780 166636 575144 0 0 0 2552 1001 2131 0
2 50 49 0
0 1 140 24780 166636 575144 0 0 0 3188 1233 2755 0
3 49 48 0
0 1 140 24780 166636 575144 0 0 0 2048 868 1812 0
2 49 49 0
0 1 140 24780 166636 575144 0 0 0 2720 1094 2386 0
3 49 49 0
As you can see, almost 50% of the CPU is waiting on I/O. This doesn't
seem like it should be happening, however, since we are using a RAID
1 setup (160+160). We have 1GB ram, and have upped shared_buffers to
13000 and work_mem to 8096. What would cause the computer to only use
such a small percentage of the CPU, with more than half of it waiting
on I/O requests?
Thanks a lot
Jason
^ permalink raw reply [nested|flat] 13+ messages in thread
* Re: Slow Postgresql server
@ 2007-04-12 04:34 Dennis Bjorklund <db@zigo.dhs.org>
parent: Jason Lustig <lustig@brandeis.edu>
2 siblings, 0 replies; 13+ messages in thread
From: Dennis Bjorklund @ 2007-04-12 04:34 UTC (permalink / raw)
To: Jason Lustig <lustig@brandeis.edu>; +Cc: pgsql-performance
Jason Lustig skrev:
> and work_mem to 8096. What would cause the computer to only use such a
> small percentage of the CPU, with more than half of it waiting on I/O
> requests?
Do your webpages write things to the database on each connect?
Maybe it do a bunch of writes each individually commited? For every
commit pg will wait for the data to be written down to the disk platter
before it move on. So if you do several writes you want to do them in
one transaction so you only need one commit.
/Dennis
^ permalink raw reply [nested|flat] 13+ messages in thread
* Re: Slow Postgresql server
@ 2007-04-12 05:33 Jeff Frost <jeff@frostconsultingllc.com>
parent: Jason Lustig <lustig@brandeis.edu>
2 siblings, 1 reply; 13+ messages in thread
From: Jeff Frost @ 2007-04-12 05:33 UTC (permalink / raw)
To: Jason Lustig <lustig@brandeis.edu>; +Cc: pgsql-performance
On Wed, 11 Apr 2007, Jason Lustig wrote:
> Hello all,
>
> My website has been having issues with our new Linux/PostgreSQL server being
> somewhat slow. I have done tests using Apache Benchmark and for pages that do
> not connect to Postgres, the speeds are much faster (334 requests/second v.
> 1-2 requests/second), so it seems that Postgres is what's causing the problem
> and not Apache. I did some reserach, and it seems that the bottleneck is in
> fact the hard drives! Here's an excerpt from vmstat:
>
> procs -----------memory---------- ---swap-- -----io---- --system--
> -----cpu------
> r b swpd free buff cache si so bi bo in cs us sy id wa
> st
> 1 1 140 24780 166636 575144 0 0 0 3900 1462 3299 1 4 49 48
> 0
> 0 1 140 24780 166636 575144 0 0 0 3828 1455 3391 0 4 48 48
> 0
> 1 1 140 24780 166636 575144 0 0 0 2440 960 2033 0 3 48 48
> 0
> 0 1 140 24780 166636 575144 0 0 0 2552 1001 2131 0 2 50 49
> 0
> 0 1 140 24780 166636 575144 0 0 0 3188 1233 2755 0 3 49 48
> 0
> 0 1 140 24780 166636 575144 0 0 0 2048 868 1812 0 2 49 49
> 0
> 0 1 140 24780 166636 575144 0 0 0 2720 1094 2386 0 3 49 49
> 0
>
> As you can see, almost 50% of the CPU is waiting on I/O. This doesn't seem
> like it should be happening, however, since we are using a RAID 1 setup
> (160+160). We have 1GB ram, and have upped shared_buffers to 13000 and
> work_mem to 8096. What would cause the computer to only use such a small
> percentage of the CPU, with more than half of it waiting on I/O requests?
Well, the simple answer is a slow disk subsystem. Is it hardware or software
RAID1? If hardware, what's the RAID controller? Based on your vmstat output,
I'd guess that this query activity is all writes since I see only blocks out.
Can you identify what the slow queries are? What version of postgres? How
large is the database? Can you post the non-default values in your
postgresql.conf?
I'd suggest you test your disk subsystem to see if it's as performant as you
think with bonnie++. Here's some output from my RAID1 test server:
Version 1.03 ------Sequential Output------ --Sequential Input- --Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
pgtest 4G 47090 92 52348 11 30954 6 41838 65 73396 8 255.9 1
------Sequential Create------ --------Random Create--------
-Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
16 894 2 +++++ +++ 854 1 817 2 +++++ +++ 969 2
So, that's 52MB/sec block writes and 73MB/sec block reads. That's typical of
a RAID1 on 2 semi-fast SATA drives.
If you're doing writes to the DB on every web page, you might consider playing
with the commit_delay and commit_siblings parameters in the postgresql.conf.
Also, if you're doing multiple inserts as separate transactions, you should
consider batching them up in one transaction.
--
Jeff Frost, Owner <jeff@frostconsultingllc.com>
Frost Consulting, LLC http://www.frostconsultingllc.com/
Phone: 650-780-7908 FAX: 650-649-1954
^ permalink raw reply [nested|flat] 13+ messages in thread
* Re: Slow Postgresql server
@ 2007-04-12 13:26 Ron <rjpeace@earthlink.net>
parent: Jason Lustig <lustig@brandeis.edu>
2 siblings, 1 reply; 13+ messages in thread
From: Ron @ 2007-04-12 13:26 UTC (permalink / raw)
To: Jason Lustig <lustig@brandeis.edu>; +Cc: pgsql-performance
1= RAID 1improves data =intregrity=, not IO performance.
Your HD IO performance is essentially that of 1 160GB HD of whatever
performance one of those HDs have.
(what kind of HDs are they anyway? For instance 7200rpm 160GB HDs
are not particularly "high performance")
BEST case is streaming IO involving no seeks => ~50 MBps.
You can't get even that as the back end of a website.
2= 1GB of RAM is -small- for a DB server.
You need to buy RAM and HD.
Boost the RAM to 4GB, change pg config parameters appropriately and
see how much it helps.
Non ECC RAM is currently running ~$60-$75 per GB for 1 or 2 GB sticks
ECC RAM prices will be ~ 1.5x - 2x that, $120 - $150 per GB for 1 or
2 GB sticks.
(do !not! buy 4GB sticks unless you have a large budget. Their price
pr GB is still too high)
If adding RAM helps as much as I suspect it will, find out how big
the "hot" section of your DB is and see if you can buy enough RAM to
make it RAM resident.
If you can do this, it will result in the lowest term DB maintenance.
If you can't do that for whatever reason, the next step is to improve
your HD subsystem.
Cheap RAID cards with enough BB cache to allow writes to be coalesced
into larger streams (reducing seeks) will help, but you fundamentally
you will need more HDs.
RAID 5 is an reasonable option for most website DBs workloads.
To hit the 300MBps speeds attainable by the cheap RAID cards, you are
going to at least 7 HDs (6 HDs * 50MBps ASTR = 300MBps ASTR + the
equivalent of 1 HD gets used for the "R" in RAID). A minimum of 8
HDs are need for this performance if you want to use RAID 6.
Most tower case (not mini-tower, tower) cases can hold this internally.
Price per MBps of HD is all over the map. The simplest (but not
necessarily best) option is to buy more of the 160GB HDs you already have.
Optimizing the money spent when buying HDs for a RAID set is a bit
more complicated than doing so for RAM. Lot's of context dependent
things affect the final decision.
I see you are mailing from Brandeis. I'm local. Drop me some
private email at the address I'm posting from if you want and I'll
send you further contact info so we can talk in more detail.
Cheers,
Ron Peacetree
At 06:02 PM 4/11/2007, Jason Lustig wrote:
>Hello all,
>
>My website has been having issues with our new Linux/PostgreSQL
>server being somewhat slow. I have done tests using Apache Benchmark
>and for pages that do not connect to Postgres, the speeds are much
>faster (334 requests/second v. 1-2 requests/second), so it seems that
>Postgres is what's causing the problem and not Apache. I did some
>reserach, and it seems that the bottleneck is in fact the hard
>drives! Here's an excerpt from vmstat:
>
>procs -----------memory---------- ---swap-- -----io---- --system--
>-----cpu------
>r b swpd free buff cache si so bi bo in cs us
>sy id wa st
>1 1 140 24780 166636 575144 0 0 0 3900 1462 3299 1
>4 49 48 0
>0 1 140 24780 166636 575144 0 0 0 3828 1455 3391 0
>4 48 48 0
>1 1 140 24780 166636 575144 0 0 0 2440 960 2033 0
>3 48 48 0
>0 1 140 24780 166636 575144 0 0 0 2552 1001 2131 0
>2 50 49 0
>0 1 140 24780 166636 575144 0 0 0 3188 1233 2755 0
>3 49 48 0
>0 1 140 24780 166636 575144 0 0 0 2048 868 1812 0
>2 49 49 0
>0 1 140 24780 166636 575144 0 0 0 2720 1094 2386 0
>3 49 49 0
>
>As you can see, almost 50% of the CPU is waiting on I/O. This doesn't
>seem like it should be happening, however, since we are using a RAID
>1 setup (160+160). We have 1GB ram, and have upped shared_buffers to
>13000 and work_mem to 8096. What would cause the computer to only use
>such a small percentage of the CPU, with more than half of it waiting
>on I/O requests?
>
>Thanks a lot
>Jason
>
>
>---------------------------(end of broadcast)---------------------------
>TIP 1: 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
^ permalink raw reply [nested|flat] 13+ messages in thread
* Re: Slow Postgresql server
@ 2007-04-12 14:08 Guido Neitzer <lists@event-s.net>
parent: Ron <rjpeace@earthlink.net>
0 siblings, 1 reply; 13+ messages in thread
From: Guido Neitzer @ 2007-04-12 14:08 UTC (permalink / raw)
To: pgsql-performance
On 12.04.2007, at 07:26, Ron wrote:
> You need to buy RAM and HD.
Before he does that, wouldn't it be more useful, to find out WHY he
has so much IO?
Have I missed that or has nobody suggested finding the slow queries
(when you have much IO on them, they might be slow at least with a
high shared memory setting).
So, my first idea is, to turn on query logging for queries longer
than a xy milliseconds, "explain analyse" these queries and see
wether there are a lot of seq scans involved, which would explain the
high IO.
Just an idea, perhaps I missed that step in that discussion
somewhere ...
But yes, it might also be, that the server is swapping, that's
another thing to find out.
cug
^ permalink raw reply [nested|flat] 13+ messages in thread
* Re: Slow Postgresql server
@ 2007-04-12 14:59 Ron <rjpeace@earthlink.net>
parent: Guido Neitzer <lists@event-s.net>
0 siblings, 1 reply; 13+ messages in thread
From: Ron @ 2007-04-12 14:59 UTC (permalink / raw)
To: Guido Neitzer <lists@event-s.net>; +Cc: pgsql-performance
At 10:08 AM 4/12/2007, Guido Neitzer wrote:
>On 12.04.2007, at 07:26, Ron wrote:
>
>>You need to buy RAM and HD.
>
>Before he does that, wouldn't it be more useful, to find out WHY he
>has so much IO?
1= Unless I missed something, the OP described pg being used as a
backend DB for a webserver.
I know the typical IO demands of that scenario better than I sometimes want to.
:-(
2= 1GB of RAM + effectively 1 160GB HD = p*ss poor DB IO support.
~ 1/2 that RAM is going to be used for OS stuff, leaving only ~512MB
of RAM to be used supporting pg.
That RAID 1 set is effectively 1 HD head that all IO requests are
going to contend for.
Even if the HD in question is a 15Krpm screamer, that level of HW
contention has very adverse implications.
Completely agree that at some point the queries need to be examined
(ditto the table schema, etc), but this system is starting off in a
Bad Place for its stated purpose IME.
Some minimum stuff is obvious even w/o spending time looking at
anything beyond the HW config.
Cheers,
Ron Peacetree
>Have I missed that or has nobody suggested finding the slow queries
>(when you have much IO on them, they might be slow at least with a
>high shared memory setting).
>
>So, my first idea is, to turn on query logging for queries longer
>than a xy milliseconds, "explain analyse" these queries and see
>wether there are a lot of seq scans involved, which would explain the
>high IO.
>
>Just an idea, perhaps I missed that step in that discussion
>somewhere ...
>
>But yes, it might also be, that the server is swapping, that's
>another thing to find out.
>
>cug
>
>---------------------------(end of broadcast)---------------------------
>TIP 3: Have you checked our extensive FAQ?
>
> http://www.postgresql.org/docs/faq
^ permalink raw reply [nested|flat] 13+ messages in thread
* Re: Slow Postgresql server
@ 2007-04-12 15:19 Guido Neitzer <lists@event-s.net>
parent: Ron <rjpeace@earthlink.net>
0 siblings, 1 reply; 13+ messages in thread
From: Guido Neitzer @ 2007-04-12 15:19 UTC (permalink / raw)
To: Ron <rjpeace@earthlink.net>; pgsql-performance
On 12.04.2007, at 08:59, Ron wrote:
> 1= Unless I missed something, the OP described pg being used as a
> backend DB for a webserver.
Yep.
> I know the typical IO demands of that scenario better than I
> sometimes want to.
> :-(
Yep. Same here. ;-)
> 2= 1GB of RAM + effectively 1 160GB HD = p*ss poor DB IO support.
Absolutely right. Depending a little bit on the DB and WebSite layout
and on the actual requirements, but yes - it's not really a kick-ass
machine ...
> Completely agree that at some point the queries need to be examined
> (ditto the table schema, etc), but this system is starting off in a
> Bad Place for its stated purpose IME.
> Some minimum stuff is obvious even w/o spending time looking at
> anything beyond the HW config.
Depends. As I said - if the whole DB fits into the remaining space,
and a lot of website backend DBs do, it might just work out. But this
seems not to be the case - either the site is chewing on seq scans
all the time which will cause I/O or it is bound by the lack of
memory and swaps the whole time ... He has to find out.
cug
^ permalink raw reply [nested|flat] 13+ messages in thread
* Re: Slow Postgresql server
@ 2007-04-12 15:35 Jeff Frost <jeff@frostconsultingllc.com>
parent: Jeff Frost <jeff@frostconsultingllc.com>
0 siblings, 1 reply; 13+ messages in thread
From: Jeff Frost @ 2007-04-12 15:35 UTC (permalink / raw)
To: Jason Lustig <lustig@brandeis.edu>; +Cc: pgsql-performance
On Thu, 12 Apr 2007, Jason Lustig wrote:
> 0 <-- BM starts here
> 10 0 180 700436 16420 91740 0 0 0 176 278 2923 59 41 0
> 0 0
> 11 0 180 696736 16420 91740 0 0 0 0 254 2904 57 43 0
> 0 0
> 12 0 180 691272 16420 91740 0 0 0 0 255 3043 60 39 1
> 0 0
> 9 0 180 690396 16420 91740 0 0 0 0 254 3078 63 36 2 0
> 0
>
> Obviously, I've turned off logging now but I'd like to get it running again
> (without bogging down the server) so that I can profile the system and find
> out which queries I need to optimize. My logging settings (with unnecessary
> comments taken out) were:
So what did you get in the logs when you had logging turned on? If you have
the statement logging, perhaps it's worth running through pgfouine to generate
a report.
>
> log_destination = 'syslog' # Valid values are combinations of
> redirect_stderr = off # Enable capturing of stderr into log
> log_min_duration_statement = 0 # -1 is disabled, 0 logs all
> statements
> silent_mode = on # DO NOT USE without syslog or
> log_duration = off
> log_line_prefix = 'user=%u,db=%d' # Special values:
> log_statement = 'none' # none, ddl, mod, all
>
Perhaps you just want to log slow queries > 100ms? But since you don't seem
to know what queries you're running on each web page, I'd suggest you just
turn on the following and run your benchmark against it, then turn it back
off:
log_duration = on
log_statement = 'all'
Then go grab pgfouine and run the report against the logs to see what queries
are chewing up all your time.
> So you know, we're using Postgres 8.2.3. The database currently is pretty
> small (we're just running a testing database right now with a few megabytes
> of data). No doubt some of our queries are slow, but I was concerned because
> no matter how slow the queries were (at most the worst were taking a couple
> of msecs anyway), I was getting ridiculously slow responses from the server.
> Outside of logging, our only other non-default postgresql.conf items are:
>
> shared_buffers = 13000 # min 128kB or max_connections*16kB
> work_mem = 8096 # min 64kB
>
> In terms of the server itself, I think that it uses software raid. How can I
> tell? Our hosting company set it up with the server so I guess I could ask
> them, but is there a program I can run which will tell me the information? I
> also ran bonnie++ and got this output:
>
> Version 1.03 ------Sequential Output------ --Sequential Input-
> --Random-
> -Per Chr- --Block-- -Rewrite- -Per Chr- --Block--
> --Seeks--
> Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec
> %CP
> pgtest 2000M 29277 67 33819 15 15446 4 35144 62 48887 5 152.7 0
> ------Sequential Create------ --------Random
> Create--------
> -Create-- --Read--- -Delete-- -Create-- --Read---
> -Delete--
> files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec
> %CP
> 16 17886 77 +++++ +++ +++++ +++ 23258 99 +++++ +++ +++++
> +++
>
> So I'm getting 33MB and 48MB write/read respectively. Is this slow? Is there
> anything I should be doing to optimize our RAID configuration?
>
It's not fast, but at least it's about the same speed as an average IDE drive
from this era. More disks would help, but since you indicate the DB fits in
RAM with plenty of room to spare, how about you update your
effective_cache_size to something reasonable. You can use the output of the
'free' command and take the cache number and divide by 8 to get a reasonable
value on linux. Then turn on logging and run your benchmark. After that, run
a pgfouine report against the log and post us the explain analyze from your
slow queries.
And if Ron is indeed local, it might be worthwhile to contact him. Someone
onsite would likely get this taken care of much faster than we can on the
mailing list.
--
Jeff Frost, Owner <jeff@frostconsultingllc.com>
Frost Consulting, LLC http://www.frostconsultingllc.com/
Phone: 650-780-7908 FAX: 650-649-1954
^ permalink raw reply [nested|flat] 13+ messages in thread
* Re: Slow Postgresql server
@ 2007-04-12 16:56 Scott Marlowe <smarlowe@g2switchworks.com>
parent: Guido Neitzer <lists@event-s.net>
0 siblings, 1 reply; 13+ messages in thread
From: Scott Marlowe @ 2007-04-12 16:56 UTC (permalink / raw)
To: Guido Neitzer <lists@event-s.net>; +Cc: Ron <rjpeace@earthlink.net>; pgsql-performance
On Thu, 2007-04-12 at 10:19, Guido Neitzer wrote:
> On 12.04.2007, at 08:59, Ron wrote:
>
> Depends. As I said - if the whole DB fits into the remaining space,
> and a lot of website backend DBs do, it might just work out. But this
> seems not to be the case - either the site is chewing on seq scans
> all the time which will cause I/O or it is bound by the lack of
> memory and swaps the whole time ... He has to find out.
It could also be something as simple as a very bloated data store.
I'd ask the user what vacuum verbose says at the end
^ permalink raw reply [nested|flat] 13+ messages in thread
* Re: Slow Postgresql server
@ 2007-04-12 17:03 Jeff Frost <jeff@frostconsultingllc.com>
parent: Scott Marlowe <smarlowe@g2switchworks.com>
0 siblings, 1 reply; 13+ messages in thread
From: Jeff Frost @ 2007-04-12 17:03 UTC (permalink / raw)
To: Jason Lustig <lustig@brandeis.edu>; Scott Marlowe <smarlowe@g2switchworks.com>; +Cc: Guido Neitzer <lists@event-s.net>; Ron <rjpeace@earthlink.net>; pgsql-performance
On Thu, 12 Apr 2007, Scott Marlowe wrote:
> On Thu, 2007-04-12 at 10:19, Guido Neitzer wrote:
>> On 12.04.2007, at 08:59, Ron wrote:
>
>>
>> Depends. As I said - if the whole DB fits into the remaining space,
>> and a lot of website backend DBs do, it might just work out. But this
>> seems not to be the case - either the site is chewing on seq scans
>> all the time which will cause I/O or it is bound by the lack of
>> memory and swaps the whole time ... He has to find out.
>
> It could also be something as simple as a very bloated data store.
>
> I'd ask the user what vacuum verbose says at the end
You know, I should answer emails at night...we didn't ask when the last time
the data was vacuumed or analyzed and I believe he indicated that the only
non-default values were memory related, so no autovacuum running.
Jason,
Before you go any further, run 'vacuum analyze;' on your DB if you're not
doing this with regularity and strongly consider enabling autovacuum.
--
Jeff Frost, Owner <jeff@frostconsultingllc.com>
Frost Consulting, LLC http://www.frostconsultingllc.com/
Phone: 650-780-7908 FAX: 650-649-1954
^ permalink raw reply [nested|flat] 13+ messages in thread
* Re: Slow Postgresql server
@ 2007-04-12 19:10 Carlos Moreno <moreno_pg@mochima.com>
parent: Jeff Frost <jeff@frostconsultingllc.com>
0 siblings, 0 replies; 13+ messages in thread
From: Carlos Moreno @ 2007-04-12 19:10 UTC (permalink / raw)
To: Jeff Frost <jeff@frostconsultingllc.com>; +Cc: pgsql-performance
Jeff Frost wrote:
>
> You know, I should answer emails at night...
Indeed you shouldN'T ;-)
Carlos
--
^ permalink raw reply [nested|flat] 13+ messages in thread
* Re: Slow Postgresql server
@ 2007-04-12 21:58 Jason Lustig <lustig@brandeis.edu>
parent: Jeff Frost <jeff@frostconsultingllc.com>
0 siblings, 1 reply; 13+ messages in thread
From: Jason Lustig @ 2007-04-12 21:58 UTC (permalink / raw)
To: Jeff Frost <jeff@frostconsultingllc.com>; +Cc: pgsql-performance
Hi all,
Wow! That's a lot to respond to. Let me go through some of the
ideas... First, I just turned on autovacuum, I forgot to do that. I'm
not seeing a major impact though. Also, I know that it's not optimal
for a dedicated server. It's not just for postgres, it's also got our
apache server on it. We're just getting started and didn't want to
make the major investment right now in getting the most expensive
server we can get. Within the next year, as our traffic grows, we
will most likely upgrade, but for now when we're in the beginning
phases of our project, we're going to work with this server.
In terms of RAID not helping speed-wise (only making an impact in
data integrity) - I was under the impression that even a mirrored
disk set improves speed, because read requests can be sent to either
of the disk controllers. Is this incorrect?
I turned on logging again, only logging queries > 5ms. and it caused
the same problems. I think it might be an issue within the OS's
logging facilities, since it's going through stderr.
Some of the queries are definitely making an impact on the speed. We
are constantly trying to improve performance, and part of that is
reassessing our indexes and denormalizing data where it would help.
We're also doing work with memcached to cache the results of some of
the more expensive operations.
Thanks for all your help guys - it's really fantastic to see the
community here! I've got a lot of database experience (mostly with ms
sql and mysql) but this is my first time doing serious work with
postgres and it's really a great system with great people too.
Jason
On Apr 12, 2007, at 11:35 AM, Jeff Frost wrote:
> On Thu, 12 Apr 2007, Jason Lustig wrote:
>
>> 0 <-- BM starts here
>> 10 0 180 700436 16420 91740 0 0 0 176 278 2923
>> 59 41 0 0 0
>> 11 0 180 696736 16420 91740 0 0 0 0 254 2904
>> 57 43 0 0 0
>> 12 0 180 691272 16420 91740 0 0 0 0 255 3043
>> 60 39 1 0 0
>> 9 0 180 690396 16420 91740 0 0 0 0 254 3078
>> 63 36 2 0 0
>>
>> Obviously, I've turned off logging now but I'd like to get it
>> running again (without bogging down the server) so that I can
>> profile the system and find out which queries I need to optimize.
>> My logging settings (with unnecessary comments taken out) were:
>
> So what did you get in the logs when you had logging turned on? If
> you have the statement logging, perhaps it's worth running through
> pgfouine to generate a report.
>
>>
>> log_destination = 'syslog' # Valid values are
>> combinations of
>> redirect_stderr = off # Enable capturing of
>> stderr into log
>> log_min_duration_statement = 0 # -1 is disabled, 0
>> logs all statements
>> silent_mode = on # DO NOT USE without
>> syslog or
>> log_duration = off
>> log_line_prefix = 'user=%u,db=%d' # Special
>> values:
>> log_statement = 'none' # none, ddl, mod, all
>>
>
> Perhaps you just want to log slow queries > 100ms? But since you
> don't seem to know what queries you're running on each web page,
> I'd suggest you just turn on the following and run your benchmark
> against it, then turn it back off:
>
> log_duration = on
> log_statement = 'all'
>
> Then go grab pgfouine and run the report against the logs to see
> what queries are chewing up all your time.
>
>> So you know, we're using Postgres 8.2.3. The database currently is
>> pretty small (we're just running a testing database right now with
>> a few megabytes of data). No doubt some of our queries are slow,
>> but I was concerned because no matter how slow the queries were
>> (at most the worst were taking a couple of msecs anyway), I was
>> getting ridiculously slow responses from the server. Outside of
>> logging, our only other non-default postgresql.conf items are:
>>
>> shared_buffers = 13000 # min 128kB or
>> max_connections*16kB
>> work_mem = 8096 # min 64kB
>>
>> In terms of the server itself, I think that it uses software raid.
>> How can I tell? Our hosting company set it up with the server so I
>> guess I could ask them, but is there a program I can run which
>> will tell me the information? I also ran bonnie++ and got this
>> output:
>>
>> Version 1.03 ------Sequential Output------ --Sequential
>> Input- --Random-
>> -Per Chr- --Block-- -Rewrite- -Per Chr- --
>> Block-- --Seeks--
>> Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %
>> CP /sec %CP
>> pgtest 2000M 29277 67 33819 15 15446 4 35144 62 48887 5
>> 152.7 0
>> ------Sequential Create------ --------Random
>> Create--------
>> -Create-- --Read--- -Delete-- -Create-- --
>> Read--- -Delete--
>> files /sec %CP /sec %CP /sec %CP /sec %CP /sec %
>> CP /sec %CP
>> 16 17886 77 +++++ +++ +++++ +++ 23258 99 +++++ ++
>> + +++++ +++
>>
>> So I'm getting 33MB and 48MB write/read respectively. Is this
>> slow? Is there anything I should be doing to optimize our RAID
>> configuration?
>>
>
> It's not fast, but at least it's about the same speed as an average
> IDE drive from this era. More disks would help, but since you
> indicate the DB fits in RAM with plenty of room to spare, how about
> you update your effective_cache_size to something reasonable. You
> can use the output of the 'free' command and take the cache number
> and divide by 8 to get a reasonable value on linux. Then turn on
> logging and run your benchmark. After that, run a pgfouine report
> against the log and post us the explain analyze from your slow
> queries.
>
> And if Ron is indeed local, it might be worthwhile to contact him.
> Someone onsite would likely get this taken care of much faster than
> we can on the mailing list.
>
> --
> Jeff Frost, Owner <jeff@frostconsultingllc.com>
> Frost Consulting, LLC http://www.frostconsultingllc.com/
> Phone: 650-780-7908 FAX: 650-649-1954
^ permalink raw reply [nested|flat] 13+ messages in thread
* Re: Slow Postgresql server
@ 2007-04-12 22:18 Guido Neitzer <lists@event-s.net>
parent: Jason Lustig <lustig@brandeis.edu>
0 siblings, 0 replies; 13+ messages in thread
From: Guido Neitzer @ 2007-04-12 22:18 UTC (permalink / raw)
To: Jason Lustig <lustig@brandeis.edu>; +Cc: pgsql-performance
On 12.04.2007, at 15:58, Jason Lustig wrote:
> Wow! That's a lot to respond to. Let me go through some of the
> ideas... First, I just turned on autovacuum, I forgot to do that.
> I'm not seeing a major impact though. Also, I know that it's not
> optimal for a dedicated server.
Hmm, why not? Have you recently vacuumed your db manually so it gets
cleaned up? Even a vacuum full might be useful if the db is really
bloated.
> It's not just for postgres, it's also got our apache server on it.
> We're just getting started and didn't want to make the major
> investment right now in getting the most expensive server we can get
Hmmm, but more RAM would definitely make sense, especially in that
szenaria. It really sounds like you machine is swapping to dead.
What does the system say about memory usage?
> Some of the queries are definitely making an impact on the speed.
> We are constantly trying to improve performance, and part of that
> is reassessing our indexes and denormalizing data where it would
> help. We're also doing work with memcached to cache the results of
> some of the more expensive operations.
Hmmm, that kills you even more, as it uses RAM. I really don't think
at the moment that it has something to do with PG itself, but with
not enough memory for what you want to achieve.
What perhaps helps might be connection pooling, so that not so many
processes are created for the requests. It depends on your "middle-
ware" what you can do about that. pg_pool might be an option.
cug
^ permalink raw reply [nested|flat] 13+ messages in thread
end of thread, other threads:[~2007-04-12 22:18 UTC | newest]
Thread overview: 13+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2007-04-11 22:02 Slow Postgresql server Jason Lustig <lustig@brandeis.edu>
2007-04-12 04:34 ` Dennis Bjorklund <db@zigo.dhs.org>
2007-04-12 05:33 ` Jeff Frost <jeff@frostconsultingllc.com>
2007-04-12 15:35 ` Jeff Frost <jeff@frostconsultingllc.com>
2007-04-12 21:58 ` Jason Lustig <lustig@brandeis.edu>
2007-04-12 22:18 ` Guido Neitzer <lists@event-s.net>
2007-04-12 13:26 ` Ron <rjpeace@earthlink.net>
2007-04-12 14:08 ` Guido Neitzer <lists@event-s.net>
2007-04-12 14:59 ` Ron <rjpeace@earthlink.net>
2007-04-12 15:19 ` Guido Neitzer <lists@event-s.net>
2007-04-12 16:56 ` Scott Marlowe <smarlowe@g2switchworks.com>
2007-04-12 17:03 ` Jeff Frost <jeff@frostconsultingllc.com>
2007-04-12 19:10 ` Carlos Moreno <moreno_pg@mochima.com>
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