Andres Freund <andres@anarazel.de> writes:
> On 2018-01-12 10:45:54 -0500, Tom Lane wrote:
>> The xl_prev field is our only way of detecting that we're looking at
>> old WAL data when we cross a sector boundary.
> Right. I wonder if it be reasonable to move that to a page's header
> instead of individual records? To avoid torn page issues we'd have to
> reduce the page size to a sector size, but I'm not sure that's that bad?
Giving up a dozen or two bytes out of every 512 sounds like quite an
overhead. Also, this'd mean that a much larger fraction of WAL records
need to be split across page boundaries, which I'd expect to produce a
performance hit in itself --- a page crossing has to complicate figuring
out how much space we need for the record.
regards, tom lane