Re: New XLOG record indicating WAL-skipping

On Fri, Jan 15, 2010 at 8:28 PM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> I don't like special-casing UNLOGGED records in XLogInsert and
> ReadRecord(). Those functions are complicated enough already. The
> special handling from XLogInsert() (and a few other places) is only
> required because the UNLOGGED records carry no payload. That's easy to
> avoid, just add some payload to them, doesn't matter what it is. And I
> don't think ReadRecord() is the right place to emit the errors/warnings,
> that belongs naturally in xlog_redo().
>
> It might be useful to add some information in the records telling why
> WAL-logging was skipped. It might turn out to be useful in debugging.
> That also conveniently adds payload to the records, to avoid the
> special-casing in XLogInsert() :-).
>
> I think it's a premature optimization to skip writing the records if
> we've written in the same session already. Especially with the 'reason'
> information added to the records, it's nice to have a record of each
> such operation. All operations that skip WAL-logging are heavy enough
> that an additional WAL record will make no difference. I can see that it
> was required to avoid the flooding from heap_insert(), but we can move
> the XLogSkipLogging() call from heap_insert() to heap_sync().
>
> Attached is an updated patch, doing the above. Am I missing anything?

Thanks a lot! Your change seems to be OK.

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center