Gregory Stark wrote:
> "Ron St-Pierre" <ron.pgsql@shaw.ca> writes:
>
>
>> We vacuum only a few of our tables nightly, this one is the last one because it
>> takes longer to run. I'll probably re-index it soon, but I would appreciate any
>> advice on how to speed up the vacuum process (and the db in general).
>>
> ...
>
>> vacuum_cost_delay = 200
>>
>
> Well speeding up vacuum isn't really useful in itself. In fact you have vacuum
> configured to run quite slowly by having vacuum_cost_delay set so high. You
> have it set to sleep 200ms every few pages. If you lower that it'll run faster
> but take more bandwidth away from the foreground tasks.
>
It's okay if it uses a lot of resources, because it's scheduled to run
during the night (our slow time). Because most of the important queries
running during the day use this table, I want the vacuum analzye
finished ASAP.
>
>> Here's the table information:
>> The table has 140,000 rows, 130 columns (mostly NUMERIC), 60 indexes.
>>
>
> For what it's worth NUMERIC columns take more space than you might expect.
> Figure a minimum of 12 bytes your rows are at about 1.5k each even if the
> non-numeric columns aren't large themselves. What are the other columns?
>
The NUMERIC columns hold currency related values, with values ranging
from a few cents to the billions, as well as a few negative numbers.
>
>> We were running autovacuum but it interfered with the updates to we shut it
>> off.
>>
>
> Was it just the I/O bandwidth? I'm surprised as your vacuum_cost_delay is
> quite high. Manual vacuum doesn't do anything differently from autovacuum,
> neither should interfere directly with updates except by taking away
> I/O bandwidth.
>
>
I don't know what the problem was. I tried to exclude certain tables
from autovacuuming, but it autovacuumed anyway.

>> We vacuum this table nightly, and it currently takes about 12 hours to
>> vacuum it. Not much else is running during this period, nothing that should
>> affect the table.
>>
>
> Is this time increasing over time? If once a day isn't enough then you may be
> accumulating more and more dead space over time. In which case you may be
> better off running it during prime time with a large vacuum_cost_delay (like
> the 200 you have configured) rather than trying to get to run fast enough to
> fit in the off-peak period.
>
>
>> deadlock_timeout = 10000
>>
>
> I would not suggest having this quite this high. Raising it from the default
> is fine but having a value larger than your patience is likely to give you the
> false impression that something is hung if you should ever get a deadlock.
>
>
Good point. I'll look into this.

Thanks

Ron


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Alvaro Herrera wrote:
> Ron St-Pierre wrote:
>
>
>> Okay, here's our system:
>> postgres 8.1.4
>>
>
> Upgrade to 8.1.10
>
Any particular fixes in 8.1.10 that would help with this?
>
>> Here's the table information:
>> The table has 140,000 rows, 130 columns (mostly NUMERIC), 60 indexes.
>>
>
> 60 indexes? You gotta be kidding. You really have 60 columns on which
> to scan?
>
>
Really. 60 indexes. They're the most commonly requested columns for
company information (we believe). Any ideas on testing our assumptions
about that? I would like to know definitively what are the most popular
columns. Do you think that rules would be a good approach for this?
(Sorry if I'm getting way off topic here)
>> vacuum_cost_delay = 200
>> vacuum_cost_limit = 100
>>
>
> Isn't this a bit high? What happens if you cut the delay to, say, 10?
> (considering you've lowered the limit to half the default)
>
>
Yes, Tom pointed this out too. I'll lower it and check out the results.

Ron


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On Tue, 23 Oct 2007 10:00:05 -0700
Ron St-Pierre <ron.pgsql@shaw.ca> wrote:

> Alvaro Herrera wrote:
> > Ron St-Pierre wrote:
> >
> >
> >> Okay, here's our system:
> >> postgres 8.1.4
> >>
> >
> > Upgrade to 8.1.10
> >
> Any particular fixes in 8.1.10 that would help with this?
> >
> >> Here's the table information:
> >> The table has 140,000 rows, 130 columns (mostly NUMERIC), 60
> >> indexes.
> >
> > 60 indexes? You gotta be kidding. You really have 60 columns on
> > which to scan?
> >
> >
> Really. 60 indexes. They're the most commonly requested columns for
> company information (we believe). Any ideas on testing our
> assumptions about that? I would like to know definitively what are
> the most popular columns. Do you think that rules would be a good
> approach for this? (Sorry if I'm getting way off topic here)

I suggest you:

1. Turn on stats and start looking in the stats columns to see what
indexes are actually being used.

2. Strongly review your normalization

Joshua D. Drake



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On Tue, 2007-10-23 at 08:53 -0700, Ron St-Pierre wrote:
> The table gets updated only
> about 10 times a day.

So why are you VACUUMing it nightly? You should do this at the weekend
every 3 months...

8.1 is slower at VACUUMing indexes than later releases, so 60 indexes
are going to hurt quite a lot.

The default maintenance_work_mem is sufficient for this table.

--
Simon Riggs
2ndQuadrant http://www.2ndQuadrant.com


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Ron St-Pierre wrote:
> Gregory Stark wrote:

>>> We were running autovacuum but it interfered with the updates to we
>>> shut it off.
>>
>> Was it just the I/O bandwidth? I'm surprised as your
>> vacuum_cost_delay is quite high. Manual vacuum doesn't do anything
>> differently from autovacuum, neither should interfere directly with
>> updates except by taking away I/O bandwidth.
>>
> I don't know what the problem was. I tried to exclude certain tables
> from autovacuuming, but it autovacuumed anyway.

Probably because of Xid wraparound issues. Now that you're vacuuming
weekly it shouldn't be a problem. (It's also much less of a problem in
8.2).

--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

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Ron St-Pierre wrote:
> Alvaro Herrera wrote:
>> Ron St-Pierre wrote:
>>
>>
>>> Okay, here's our system:
>>> postgres 8.1.4
>>>
>>
>> Upgrade to 8.1.10
>>
> Any particular fixes in 8.1.10 that would help with this?

I don't think so, but my guess is that you really want to avoid the
autovacuum bug which makes it vacuum without FREEZE on template0, that
has caused so many problems all over the planet.

>>> Here's the table information:
>>> The table has 140,000 rows, 130 columns (mostly NUMERIC), 60 indexes.
>>
>> 60 indexes? You gotta be kidding. You really have 60 columns on which
>> to scan?
>>
>>
> Really. 60 indexes. They're the most commonly requested columns for company
> information (we believe). Any ideas on testing our assumptions about that?
> I would like to know definitively what are the most popular columns. Do you
> think that rules would be a good approach for this? (Sorry if I'm getting
> way off topic here)

As Josh Drake already said, you can check pg_stat* views to see which
indexes are not used. Hard to say anything else without seeing the
definition.

--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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Ron St-Pierre wrote:
> We vacuum only a few of our tables nightly, this one is the last one
> because it takes longer to run. I'll probably re-index it soon, but I
> would appreciate any advice on how to speed up the vacuum process (and
> the db in general).

I am a novice to postgreSQL, so I have no answers for you. But for my own
education, I am confused by some of your post.
>
> Okay, here's our system:
> postgres 8.1.4

I have postgresql-8.1.9-1.el5

> Linux version 2.4.21

I imagine you mean Linux kernel version; I have 2.6.18-8.1.15.el5PAE

> Red Hat Linux 3.2.3

I have no clue what this means. Red Hat Linux 3 must have been in the early
1990s. RHL 5 came out about 1998 IIRC.

Red Hat Enterprise Linux 3, on the other hand, was not numbered like that,
as I recall. I no longer run that, but my current RHEL5 is named like this:

Red Hat Enterprise Linux Server release 5 (Tikanga)

and for my CentOS 4 system, it is

CentOS release 4.5 (Final)

Did RHEL3 go with the second dot in their release numbers? I do not remember
that.

> 8 GB ram
> Intel(R) Xeon(TM) CPU 3.20GHz
> Raid 5
> autovacuum=off

Why would you not have that on?

> serves as the application server and database server
> server is co-located in another city, hardware upgrade is not
> currently an option
>
> Here's the table information:
> The table has 140,000 rows, 130 columns (mostly NUMERIC), 60 indexes.

I have designed databases, infrequently, but since the late 1970s. In my
experience, my tables had relatively few columns, rarely over 10. Are you
sure this table needs so many? Why not, e.g., 13 tables averaging 10 columns
each?

OTOH, 140,000 rows is not all that many. I have a 6,000,000 row table in my
little database on my desktop, and I do not even consider that large.
Imagine the size of a database belonging to the IRS, for example. Surely it
would have at least one row for each taxpayer and each employer (possibly in
two tables, or two databases).

Here are the last few lines of a VACUUM VERBOSE; command for that little
database. The 6,000,000 row table is not in the database at the moment, nor
are some of the other tables, but two relatively (for me) large tables are.

CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO: free space map contains 166 pages in 76 relations
DETAIL: A total of 1280 page slots are in use (including overhead).
1280 page slots are required to track all free space.
Current limits are: 40000 page slots, 1000 relations, using 299 KB.
VACUUM
stock=> select count(*) from ranks; [table has 10 columns]
count
--------
981030
(1 row)

stock=> select count(*) from ibd; [table has 8 columns]
count
---------
1099789
(1 row)

And this is the time for running that psql process, most of which was
consumed by slow typing on my part.

real 1m40.206s
user 0m0.027s
sys 0m0.019s

My non-default settings for this are

# - Memory -

shared_buffers = 251000
work_mem = 32768
max_fsm_pages = 40000

I have 8GBytes RAM on this machine, and postgreSQL is the biggest memory
user. I set shared_buffers high to try to get some entire (small) tables in
RAM and to be sure there is room for indices.

--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ PGP-Key: 9A2FC99A Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http://counter.li.org
^^-^^ 08:40:01 up 1 day, 58 min, 1 user, load average: 4.08, 4.13, 4.17

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