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Re: pgbench out of memory error

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Jeff Ross wrote:
I'm trying to put a new server on line and I'm having a problem getting any kind of decent performance from it. pgbench yields around 4000 tps until scale and clients both are above 21, then I see the following: NOTICE: ALTER TABLE / ADD PRIMARY KEY will create implicit index "pgbench_accounts_pkey" for table "pgbench_accounts"
ERROR:  out of memory
DETAIL:  Failed on request of size 67108864.

You've got "maintenance_work_mem = 240MB", but it looks your OS is not allowing you to allocate more than around 64MB. Have you looked at the active ulimit settings for the accounts involved?

The controller cache is set to write thru for all three volumes because tests using dd and bonnie++ show that write thru is twice as fast as write back. I haven't dug into that any more to figure out why.

That's bizarre, and you'll never get good pgbench results that way regardless of what dd/bonnie++ say--pgbench does database commits, which is what you need the cache to accelerate, while those two tests don't. But I don't think this is relevant to your immediate problems, because you're running the select-only test so far, which isn't doing writes at all. Regardless, if I got a new system and it performed worse on dd/bonnie++ with the cache turned on, I'd send it back.

time pgbench -h $HOST -t 2000 -c $SCALE -S pgbench

Your number of transactions here is extremely low. I'd bet you're just measuring startup overhead here. Try using 20,000 per client to start instead and see what happens. On the select-only, you can easily need 1M total transactions to get an accurate reading here.

--
Greg Smith    2ndQuadrant   Baltimore, MD
PostgreSQL Training, Services and Support
greg@xxxxxxxxxxxxxxx  www.2ndQuadrant.com


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