Re: Streaming replication and pg_xlogfile_name()

On Tue, Mar 2, 2010 at 8:54 PM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> This still suffers from ambiguity around a shutdown checkpoint that
> changes the TLI. On the page the shutdown checkpoint is on, what is the
> TLI in the page header? The TLI before the checkpoint record, I presume.
> Now consider a record on the same page after the checkpoint record. It's
> on the new timeline, but pg_last_xlog_replay_location() will return the
> old TLI, because that's on the page header.

Oh, I see. You are right.

> It's not clear what it should return, a TLI corresponding the filename
> of the WAL segment the record was replayed from, so that you can use
> pg_xlogfile_name() to find out the filename of the WAL segment being
> replayed, or the accurate TLI of the record being replayed. I'm leaning
> towards the latter, it feels more correct and accurate, but you could
> argue for the former too. In any case, it needs to be well-defined.

I agree with you that the latter is more correct and accurate. The simple
fix is updating the lastPageTLI with the CheckPoint->ThisTimeLineID when
replaying the shutdown checkpoint record. Though we might need to use new
variable to keep the last applied timeline instead of the lastPageTLI.

Regards,

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