Re: VACUUM vs. REINDEX

On Fri, 7 Jul 2006, William Scott Jordan wrote:

> Hi Jeff,
>
> We are running ANALYZE with the hourly VACUUMs. Most of the time the VACUUM
> for this table looks like this:

> INFO: vacuuming "public.event_sums"
> INFO: index "event_sums_event_available" now contains 56121 row versions in
> 2256 pages
> DETAIL: 102936 index row versions were removed.
> 1777 index pages have been deleted, 1635 are currently reusable.
> CPU 0.03s/0.16u sec elapsed 1.04 sec.
> INFO: index "event_sums_date_available" now contains 56121 row versions in
> 5504 pages
> DETAIL: 102936 index row versions were removed.
> 2267 index pages have been deleted, 2202 are currently reusable.
> CPU 0.15s/0.25u sec elapsed 13.91 sec.
> INFO: index "event_sums_price_available" now contains 56121 row versions in
> 4929 pages
> DETAIL: 102936 index row versions were removed.
> 149 index pages have been deleted, 149 are currently reusable.
> CPU 0.13s/0.33u sec elapsed 0.51 sec.
> INFO: "event_sums": removed 102936 row versions in 3796 pages
> DETAIL: CPU 0.31s/0.26u sec elapsed 0.92 sec.
> INFO: "event_sums": found 102936 removable, 35972 nonremovable row versions
> in 170937 pages
> DETAIL: 8008 dead row versions cannot be removed yet.
> There were 4840134 unused item pointers.
> 0 pages are entirely empty.
> CPU 5.13s/1.68u sec elapsed 209.38 sec.
> INFO: analyzing "public.event_sums"
> INFO: "event_sums": 171629 pages, 3000 rows sampled, 7328 estimated total
> rows

Hmmm..I was looking for something that looks like this:

INFO: free space map: 109 relations, 204 pages stored; 1792 total pages
needed
DETAIL: Allocated FSM size: 1000 relations + 20000 pages = 182 kB shared
memory.
VACUUM

Maybe 7.4 doesn't give this? Or maybe you need to run vacuumdb -a -v to get
it?

> ----------------------------
>
> There are a few things in the second vacuum results that catch my eye, but I
> don't have the skill set to diagnose the problem. I do know, however, that a
> REINDEX followed by a VACUUM FULL seems to make the symptoms go away for a
> while.
>
> And I agree that we should upgrade to an 8.x version of PG, but as with many
> things in life time, money, and risk conspire against me.

You should still be able to use autovacuum, which might make you a little
happier. Which 7.4 version are you using?

>
> -William
>
>
>
>
> At 04:18 PM 7/7/2006, you wrote:
>> On Fri, 7 Jul 2006, William Scott Jordan wrote:
>>
>>> Hi all!
>>>
>>> Can anyone explain to me what VACUUM does that REINDEX doesn't? We have a
>>> frequently updated table on Postgres 7.4 on FC3 with about 35000 rows
>>> which we VACUUM hourly and VACUUM FULL once per day. It seem like the
>>> table still slows to a crawl every few weeks. Running a REINDEX by itself
>>> or a VACUUM FULL by itself doesn't seem to help, but running a REINDEX
>>> followed immediately by a VACUUM FULL seems to solve the problem.
>>>
>>> I'm trying to decide now if we need to include a daily REINDEX along with
>>> our daily VACUUM FULL, and more importantly I'm just curious to know why
>>> we should or shouldn't do that.
>>>
>>> Any information on this subject would be appreciated.
>>
>> William,
>>
>> If you're having to VACUUM FULL that often, then it's likely your FSM
>> settings are too low. What does the last few lines of VACUUM VERBOSE say?
>> Also, are you running ANALYZE with the vacuums or just running VACUUM? You
>> still need to run ANALYZE to update the planner statistics, otherwise
>> things might slowly grind to a halt. Also, you should probably consider
>> setting up autovacuum and upgrading to 8.0 or 8.1 for better performance
>> overall.
>>
>>
>> --
>> Jeff Frost, Owner <jeff(at)frostconsultingllc(dot)com>
>> Frost Consulting, LLC http://www.frostconsultingllc.com/
>> Phone: 650-780-7908 FAX: 650-649-1954
>
>
>

--
Jeff Frost, Owner <jeff(at)frostconsultingllc(dot)com>
Frost Consulting, LLC http://www.frostconsultingllc.com/
Phone: 650-780-7908 FAX: 650-649-1954