| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>, Greg Smith <gsmith(at)gregsmith(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Alan Li <ali(at)truviso(dot)com> |
| Subject: | Re: 8.4 open item: copy performance regression? |
| Date: | 2009-06-21 17:42:50 |
| Message-ID: | 15469.1245606170@sss.pgh.pa.us |
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Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> I was going to say that since we flush the WAL every 16MB anyway (at
> every XLOG file switch), you shouldn't see any benefit with larger ring
> buffers, since to fill 16MB of data you're not going to write more than
> 16MB WAL.
I'm not convinced that WAL segment boundaries are particularly relevant
to this. The unit of flushing is an 8K page, not a segment.
I wonder though whether the wal_buffers setting interacts with the
ring size. Has everyone who's tested this used the same 16MB
wal_buffers setting as in Alan's original scenario?
regards, tom lane
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