Re: High CPU Usage - PostgreSQL 7.3

On Tue, 11 Jul 2006, Jeff Frost wrote:

> On Wed, 12 Jul 2006, Neil Hepworth wrote:
>
> 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?

By the way, how big does the temp table get? If it's large, it might make the
DELETE slow because it doesn't have any indexes on any of the comparison
columns.

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

In your explain analyze from before, it seems that there were 0 rows in that
table:

> -> 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

but that was with the smaller set size I believe.

>
>>
>> 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(at)frostconsultingllc(dot)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(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