On 2-May-07, at 11:24 AM, Parks, Aaron B. wrote:
My pg 8.1 install on an AMD-64 box (4 processors) with 9 gigs of
ram running RHEL4 is acting kind of odd and I thought I would see
if anybody has any hints.
I have Java program using postgresql-8.1-409.jdbc3.jar to connect
over the network. In general it works very well. I have run batch
updates with several thousand records repeatedly that has worked fine.
The Program pulls a summation of the DB and does some processing
with it. It starts off wonderfully running a query every .5
seconds. Unfortunately, after a while it will start running
queries that take 20 to 30 seconds.
Looking at the EXPLAIN for the query no sequential scans are going
on and everything has an index that points directly at its search
criteria.
Example:
Select sum(whatever) from a inner join b on a.something=b.something
WHERE b.day=1 and b.hour=1
Select sum(whatever) from a inner join b on a.something=b.something
WHERE b.day=1 and b.hour=2
Select sum(whatever) from a inner join b on a.something=b.something
WHERE b.day=1 and b.hour=3
.
.
Select sum(whatever) from a inner join b on a.something=b.something
WHERE b.day=1 and b.hour=23
Select sum(whatever) from a inner join b on a.something=b.something
WHERE b.day=1 and b.hour=24
Select sum(whatever) from a inner join b on a.something=b.something
WHERE b.day=2 and b.hour=1
Select sum(whatever) from a inner join b on a.something=b.something
WHERE b.day=2 and b.hour=2
.
.
.
This query runs fine for a while (up to thousands of times). But
what happens is that it starts to have really nasty pauses when you
switch the day condition. After the first query with the day it
runs like a charm for 24 iterations, then slows back down again
My best guess was that an index never finished running, but REINDEX
on the table (b in this case) didn’t seem to help.
I'd think it has more to do with caching data. The first query caches
the days data, then the next day's data has to be read from disk.
Ideas?
AP
