Re: Reducing size of WAL record headers

On 9 January 2013 21:02, Heikki Linnakangas <hlinnakangas@vmware.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.

-- Simon Riggs                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services