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