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gah! sudden slowdown??

From: "SpaceBallOne" <space_ball_one(at)hotmail(dot)com>
To: <pgsql-performance(at)postgresql(dot)org>
Subject: gah! sudden slowdown??
Date: 2005-02-25 07:41:58
Message-ID: BAY14-DAV7F0C74B1FA8EB569CC211CC650@phx.gbl (view raw or flat)
Thread:
Lists: pgsql-performance
Our dual opteron has been performing well for many weeks now (after some simple tuning) when all of a sudden the queries have slowed right down!

ie:

DUAL 246 OPTERON:

select count(*) from job_archieve; - Time: 107.24 ms

explain analyse select count(*) from job_archieve;
Aggregate  (cost=2820.50..2820.50 rows=1 width=0) (actual time=153.53..153.53 rows=1 loops=1)
   ->  Seq Scan on job_archieve  (cost=0.00..2789.20 rows=12520 width=0) (actual time=1.39..132.98 rows=12520 loops=1)
 Total runtime: 153.74 msec
Time: 156.94 ms



CRAPPY AMD ATHLON XP 1700+:

select count(*) from job_archieve; - Time: 23.30 ms

explain analyse select count(*) from job_archieve;
Aggregate  (cost=2816.50..2816.50 rows=1 width=0) (actual time=133.83..133.84 rows=1 loops=1)
   ->  Seq Scan on job_archieve  (cost=0.00..2785.20 rows=12520 width=0) (actual time=0.02..72.64 rows=12520 loops=1)
 Total runtime: 133.92 msec
Time: 134.79 ms





The ratio of these simple query times is about accurate for most queries performed on the same database on the different machines... Any ideas what may have suddenly caused this and where to start troubleshooting??? Both dbs have already been fully vacuumed.

The opteron is going to get a overhaul (4 port raid going in, fresh install of freebsd, postgres etc) but would be handy to know for future reference in case this happens again....

(ps, yes i know archive is not spelt archieve ;)

Cheers!
Dave.






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