| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| 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: | 2009-06-22 07:52:47 |
| Message-ID: | 4A3F384F.6080908@enterprisedb.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
Tom Lane wrote:
> 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.
We fsync() the old WAL segment every time we switch to a new WAL
segment. That's what I meant by "flush".
If the walwriter is keeping up, it will fsync() the WAL more often, but
16MB is the maximum distance between fsync()s.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Simon Riggs | 2009-06-22 08:20:51 | Re: 8.4 open item: copy performance regression? |
| Previous Message | Brendan Jurd | 2009-06-22 07:33:24 | Re: BUG #4862: different results in to_date() between 8.3.7 & 8.4.RC1 |