Re: Reducing size of WAL record headers

On Wed, Jan 9, 2013 at 09:15:16PM +0000, Simon Riggs wrote:
> On 9 January 2013 21:02, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> wrote:
>
> >> OK, crazy idea, but can we just record xl_len as a difference against
> >> xl_tot_len, and shorten the xl_len field?
> >
> >
> > Hmm, so it would essentially be the length of all the backup blocks. perhaps
> > rename it to xl_bkpblk_len.
> >
> > However, that would cap the total size of backup blocks to 64k. Which would
> > not be enough with 32k BLCKSZ.
>
> Since that requires a recompile anyway, why not make XLogRecord
> smaller only for 16k BLCKSZ or less?
>
> Problem if we do that is that xl_len is used extensively in _redo
> routines, so its a much more invasive patch.

I would just make it int16 on <=16k block size, and int32 on >16k
blocks.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +