Re: High CPU Usage - PostgreSQL 7.3 - Mailing list pgsql-performance

On Wed, 12 Jul 2006, Neil Hepworth wrote:

> I am using version PostgreSQL 7.3.10 (RPM:
> postgresql73-rhel21-7.3.10-2 ).  Unfortunately vacuumdb -a -v does not
> give the FSM info at the end (need a newer version of postgres for
> that).  Running the same queries on 8.1 reduces the time taken to
> about 16 minutes, though I didn't run the test on the same hardware or
> OS as I want to keep my test server as close to production as
> possible, so I ran the 8.1 server on my Windows laptop (2GHz Centrino
> Duo with 2GB of RAM, yes the laptop is brand new :).

Well, looks like you're at least fairly up to date, but there is a fix in
7.3.11 that you might want to get by upgrading to 7.3.15:

     * Fix race condition in transaction log management
       There was a narrow window in which an I/O operation could be
       initiated for the wrong page, leading to an Assert failure or data
       corruption.

It also appears that you can run autovacuum with 7.3 (I thought maybe it only
went back as far as 7.4).

So, is the 16 minutes on your laptop with 8.1 for windows vs 1hr on the server
for the whole set of loops?  If so, 4x isn't a bad improvement. :-)  So,
assuming you dumped/loaded the same DB onto your laptop's postgresql server,
what does the vacuumdb -a -v say on the laptop?  Perhaps we can use it to see
if your fsm settings are ok.

BTW, did you see Scott's posting here:

http://archives.postgresql.org/pgsql-performance/2006-07/msg00091.php

Since we didn't hear from you for a while, I thought perhaps Scott had hit on
the fix.  Have you tried that yet?  It certainly would help the planner out.

You might also want to turn on autovacuum and see if that helps.

What's your disk subsystem like?  In fact, what's the entire DB server
hardware like?

>
> I run through a loop, executing the following or similar queries 8
> times (well actually 12 but the last 4 don't do anything) - Jeff I've
> attached complete outputs as files.
>
> A debug output further below (numbers after each method call name,
> above each SQL statement, are times to run that statement in
> milliseconds, the times on the lines "" are cumulative).  So total for
> one loop is 515 seconds, multiple by 8 and that gets me to over an
> hour); it is actually the deletes that take the most time; 179 seconds
> and 185 seconds each loop.
>
>                 ----------------------------------------------------
>
> CREATE TABLE fttemp670743219 AS SELECT * FROM ftone LIMIT 0
> INSERT INTO fttemp670743219 ( epId, start, direction, classid,
> consolidation, cnt )  SELECT epId, TO_TIMESTAMP(start, 'YYYY-MM-DD
> HH24:00:00.0')::timestamp AS start, direction, classid, 60 AS
> consolidation, SUM(cnt) AS cnt FROM ftone WHERE consolidation = 0 AND
> start < TO_TIMESTAMP('2006-07-11 14:04:34.156433+1000', 'YYYY-MM-DD
> HH24:00:00.0')::timestamp GROUP BY epId, direction,
> TO_TIMESTAMP(start, 'YYYY-MM-DD HH24:00:00.0')::timestamp, classid
> DELETE FROM ONLY ftone WHERE ftone.epId = fttemp670743219.epId AND
> ftone.direction = fttemp670743219.direction AND ftone.start =
> fttemp670743219.start AND ftone.consolidation =
> fttemp670743219.consolidation AND ftone.classid =
> fttemp670743219.classid
> INSERT INTO ftone ( epId, start, consolidation, direction, classid,
> cnt ) SELECT epId, start, consolidation, direction, classid, cnt FROM
> fttemp670743219
> DROP TABLE fttemp670743219
> DELETE FROM ftone WHERE consolidation = 0 AND start <
> TO_TIMESTAMP((TO_TIMESTAMP('2006-07-11 14:04: 34.156433+1000',
> 'YYYY-MM-DD 00:00:00.0')::timestamp - INTERVAL '10080 MINUTE'),
> 'YYYY-MM-DD 00:00:00.0')::timestamp
>
>                 ----------------------------------------------------
>
> ftone: 0:
> createConsolidatedInTemporary: 188:
> CREATE TABLE fttemp678233382 AS SELECT * FROM ftone LIMIT 0
> createConsolidatedInTemporary: 76783:
> INSERT INTO fttemp678233382 ( epPairdefnid, start, direction, classid,
> consolidation, cnt )  SELECT epPairdefnid, TO_TIMESTAMP(start,
> 'YYYY-MM-DD HH24:00:00.0')::timestamp AS start, direction, classid, 60
> AS consolidation, SUM(cnt) AS cnt FROM ftone WHERE consolidation = 0
> AND start < TO_TIMESTAMP('2006-07-12 11:02:13.865444+1000',
> 'YYYY-MM-DD HH24:00:00.0')::timestamp GROUP BY epPairdefnid,
> direction, TO_TIMESTAMP(start, 'YYYY-MM-DD HH24:00:00.0')::timestamp,
> classid
> replaceConsolidatedInMainTable: 179178:
> DELETE FROM ONLY ftone WHERE ftone.epPairdefnid =
> fttemp678233382.epPairdefnid AND ftone.direction =
> fttemp678233382.direction AND ftone.start = fttemp678233382.start AND
> ftone.consolidation = fttemp678233382.consolidation AND ftone.classid
> = fttemp678233382.classid
> replaceConsolidatedInMainTable: 61705:
> INSERT INTO ftone ( epPairdefnid, start, consolidation, direction,
> classid, cnt ) SELECT epPairdefnid, start, consolidation, direction,
> classid, cnt FROM fttemp678233382
> consolidate: 2656:
> DROP TABLE fttemp678233382
> MAIN LOOP TOTAL consolidate: 320526
> deleteOlderThan: 184616:
> DELETE FROM ftone WHERE consolidation = 0 AND start <
> TO_TIMESTAMP((TO_TIMESTAMP('2006-07-12 11:02:13.865444+1000',
> 'YYYY-MM-DD 00:00:00.0')::timestamp - INTERVAL '10080 MINUTE'),
> 'YYYY-MM-DD 00:00:00.0')::timestamp
> MAIN LOOP TOTAL deleteExpiredData: 505142
> MAIN LOOP TOTAL generateStatistics: 515611
>
>                 ----------------------------------------------------
>
> Thanks again,
>   Neil
>
>
> On 11/07/06, Jeff Frost <jeff@frostconsultingllc.com> wrote:
>>
>>
>> On Mon, 10 Jul 2006, Neil Hepworth wrote:
>>
>> > I should also explain that I run through these queries on multiple
>> > tables and with some slightly different parameters for the
>> > "consolidation" so I run through those 3 queries (or similar) 9 times
>> > and this takes a total of about 2 hours, with high CPU usage.  And I
>> > am running the queries from a remote Java application (using JDBC),
>> > the client is using postgresql-8.0-311.jdbc3.jar .  The explain analyse
>> > results I have provided below are from running via pgAdmin, not the
>> > Java app (I did a vacuum analyse of the db before running them):
>> >
>> >
>>
>> Neil, did you ever answer which version of 7.3 this is?
>>
>> BTW, you mentioned that this takes 2 hours, but even looping over this 9
>> times
>> seems like it would only take 9 minutes (55 seconds for the SELECT and 4
>> seconds for the DELETE = 59 seconds times 9).  Perhaps you should post the
>> explain analyze for the actual query that takes so long as the planner
>> output
>> will likely be quite different.
>>
>> One thing I noticed is that the planner seems quite incorrect about the
>> number
>> of rows it expects in the SELECT.  If you ran vacuum analyze before this,
>> perhaps your fsm settings are incorrect?  What does vacuumdb -a -v output
>> at
>> the end?  I'm 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.
>>
>> I see your fsm settings are non-default, so it's also possible I'm not used
>> to
>> reading 7.3's explain analyze output. :-)
>>
>> Also, what does vmstat output look like while the query is running?
>> Perhaps
>> you're running into some context switching problems.  It would be
>> interesting
>> to know how the query runs on 8.1.x just to know if we're chasing an
>> optimization that's fixed already in a later version.
>>
>>
>> > Subquery Scan "*SELECT*"  (cost=59690.11..62038.38 rows=23483
>> > width=16) (actual time=16861.73..36473.12 rows=560094 loops=1)
>> > ->  Aggregate  (cost= 59690.11..62038.38 rows=23483 width=16) (actual
>> > time=16861.72..34243.63 rows=560094 loops=1)
>> >       ->  Group  (cost=59690.11..61451.32 rows=234827 width=16)
>> > (actual time= 16861.62..20920.12 rows=709461 loops=1)
>> >             ->  Sort  (cost=59690.11..60277.18 rows=234827 width=16)
>> > (actual time=16861.62..18081.07 rows=709461 loops=1)
>> >                   Sort Key: eppairdefnid, "start"
>> >                   ->  Seq Scan on ftone  (cost=0.00..36446.66
>> > rows=234827 width=16) (actual time=0.45..10320.91 rows=709461 loops=1)
>> >                         Filter: ((consolidation = 60) AND ("start" <
>> > (to_timestamp('2006-07-10 18:43:27.391103+1000'::text,
>> > 'YYYY-MM-DDHH24:00:00.0'::text))::timestamp without time zone))
>> > Total runtime: 55378.68 msec
>>
>> > *** For the delete ***:
>> >
>> > Hash Join  (cost=0.00..30020.31 rows=425 width=14) (actual
>> > time=3767.47..3767.47 rows=0 loops=1)
>> > Hash Cond: ("outer".eppairdefnid = "inner".eppairdefnid)
>> > ->  Seq Scan on ftone  (cost=0.00..23583.33 rows=1286333 width=10)
>> > (actual time=0.04..2299.94 rows=1286333 loops=1)
>> > ->  Hash  (cost=0.00..0.00 rows=1 width=4) (actual
>> > time=206.01..206.01 rows=0 loops=1)
>> >       ->  Seq Scan on fttemp1600384653  (cost=0.00..0.00 rows=1
>> > width=4) (actual time=206.00..206.00 rows=0 loops=1)
>> > Total runtime: 3767.52 msec
>>
>> --
>> Jeff Frost, Owner       <jeff@frostconsultingllc.com>
>> Frost Consulting, LLC   http://www.frostconsultingllc.com/
>> Phone: 650-780-7908     FAX: 650-649-1954
>>
>

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