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Re: Group commit, revised

From: Peter Geoghegan <peter(at)2ndquadrant(dot)com>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: PG Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Group commit, revised
Date: 2012-01-17 18:15:33
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Lists: pgsql-hackers
On 17 January 2012 17:37, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> I found it very helpful to reduce wal_writer_delay in pgbench tests, when
> running with synchronous_commit=off. The reason is that hint bits don't get
> set until the commit record is flushed to disk, so making the flushes more
> frequent reduces the contention on the clog. However, Simon made async
> commits nudge WAL writer if the WAL page fills up, so I'm not sure how
> relevant that experience is anymore.

It's quite possible that the WAL Writer will spin continuously, if
given enough work to do, with this patch.

Although it's hard to tell from the graph I sent, there is a modest
improvement in TPS for even a single client. See the tables in the

Peter Geoghegan
PostgreSQL Development, 24x7 Support, Training and Services

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