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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