Re: Improving compressibility of WAL files

All that is useless until we get a %l in archive_command...

*I* didn't see an easy way to get at the "written" size later on in the
chain (i.e. in the actual archiving), so I took the path of least
resitance.

The reason *I* shy way from pg_lesslog and pg_clearxlogtail, is that
they seem to possibly be frail... I'm just scared of somethign changing
in PG some time, and my pg_clearxlogtail not nowing, me forgetting to
upgrade, and me not doing enough test of my actually restoring backups...

Sure, it's all me being neglgent, but the simpler, the better...

If I wrapped this zeroing in GUC, people could choose wether to pay the
penalty or not, would that satisfy anyone?

Again, *I* think that the force_switch case is going to happen when the
admin's quite happy to pay that penalty... But obviously not
everyone...

a.

* Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov> [090109 11:01]:
> >>> Greg Smith <gsmith(at)gregsmith(dot)com> wrote:
> > I thought at one point that the direction this was going toward was
> to
> > provide the size of the WAL file as a parameter you can use in the
> > archive_command: %p provides the path, %f the file name, and now %l
> the
> > length. That makes an example archive command something like:
> >
> > head -c "%l" "%p" | gzip > /mnt/server/archivedir/"%f"
>
> Hard to beat for performance. I thought there was some technical
> snag.
>
> > Expanding it back to always be 16MB on the other side might require
> some
> > trivial script, can't think of a standard UNIX tool suitable for that
> but
> > it's easy enough to write.
>
> Untested, but it seems like something close to this would work:
>
> cat $p $( dd if=/dev/null blocks=1 ibs=$(( (16 * 1024 * 1024) - $(stat
> -c%s $p) )) )
>
> -Kevin
>
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