Re: BUG #6528: pglesslog still referenced in docs, but no 9.1 support

Excerpts from Bruce Momjian's message of lun abr 09 15:13:10 -0300 2012:
> On Mon, Apr 09, 2012 at 10:10:34AM -0400, Robert Haas wrote:

> > This complaint appears to be accurate. I think we should go ahead and
> > remove that mention.
>
> Agreed; removed with the attached patch. I didn't bother keeping the
> gzip mention because I assume there is little value to using without
> pglesslog.

I'm not sure that assumption holds. I think you're thinking of the hack
that zeroes out the "empty" holes in the middle of data pages; those
didn't compress well unless zeroed out before compression. This tool is
not about that, but rather about removing redundant info from WAL files.
It seems to me that WAL files would be as gzip-compressible regardless
of pglesslog being applied. (Another related tool is clearxlogtail
which zeroes areas from WAL files when they are empty because of an
early switch due to archive timeout).

The funny thing is, apparently pg_lesslog was intentionally broken by
changing XLR_BKP_REMOVABLE to XLP_BKP_REMOVABLE (different semantics?)
and the fixes to make it compile again look simple. It's a bit strange
that NTT stopped maintaining the tool .. Maybe it wasn't useful anymore?

--
Álvaro Herrera <alvherre(at)commandprompt(dot)com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support