Re: UPDATEDs slowing SELECTs in a fully cached database - Mailing list pgsql-performance

From Tom Lane
Subject Re: UPDATEDs slowing SELECTs in a fully cached database
Date
Msg-id 21639.1310519797@sss.pgh.pa.us
Whole thread Raw
In response to Re: UPDATEDs slowing SELECTs in a fully cached database  (Jeff Janes <jeff.janes@gmail.com>)
List pgsql-performance
Jeff Janes <jeff.janes@gmail.com> writes:
> On 7/12/11, lars <lhofhansl@yahoo.com> wrote:
>> The fact that a select (maybe a big analytical query we'll run) touching
>> many rows will update the WAL and wait
>> (apparently) for that IO to complete is making a fully cached database
>> far less useful.
>> I just artificially created this scenario.

> I can't think of any reason that that WAL would have to be flushed
> synchronously.

Maybe he's running low on shared_buffers?  We would have to flush WAL
before writing a dirty buffer out, so maybe excessive pressure on
available buffers is part of the issue here.

            regards, tom lane

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