| From: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: XLogInsert scaling, revisited |
| Date: | 2013-07-08 09:22:22 |
| Message-ID: | 51DA84CE.1070909@vmware.com |
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| Lists: | pgsql-hackers |
On 08.07.2013 12:16, Heikki Linnakangas wrote:
> I just remembered one detail that I'm not sure has been mentioned on the
> mailing list yet. Per the commit message:
>
>> This has one user-visible change: switching to a new WAL segment with
>> pg_switch_xlog() now fills the remaining unused portion of the
>> segment with zeros. This potentially adds some overhead, but it has
>> been a very common practice by DBA's to clear the "tail" of the
>> segment with an external pg_clearxlogtail utility anyway, to make the
>> WAL files compress better. With this patch, it's no longer necessary
>> to do that.
Magnus just pointed out over IM that the above also applies to
xlog-switches caused by archive_timeout, not just pg_switch_xlog(). IOW,
all xlog-switch WAL records.
- Heikki
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