Among other possibilities, there's a known problem with slow memory
leaks in various JVM's under circumstances similar to those you are describing.
The behavior you are describing is typical of this scenario. The
increasing delay is caused by longer and longer JVM garbage
collection runs as java attempts to reclaim enough memory from a
smaller and smaller universe of available memory.
The fastest test, and possible fix, is to go and buy more RAM. See
if 16MB of RAM, heck even 10MB, makes the problem go away or delays
it's onset. If so, there's good circumstantial evidence that you are
being bitten by a slow memory leak; most likely in the JVM.
Cheers,
Ron Peacetree
At 11:24 AM 5/2/2007, 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.
Ideas?
AP
