Re: xlog filename formatting functions in recovery

On 03.07.2012 15:13, Robert Haas wrote:
> On the substance of the patch, I believe the reason why this is
> currently disallowed is because the TLI is implicitly taken from the
> running system, and on the standby that might be the wrong value.

Yeah, I believe that's the reason. So the question is, what timeline
should the functions use on a standby? With the patch as it is, they use 0:

postgres=# select pg_xlogfile_name_offset('3/FF020000');
pg_xlogfile_name_offset
-----------------------------------
(0000000000000003000000FF,131072)
(1 row)

There's a few different options:

1. current recovery_target_timeline (XLogCtl->recoveryTargetTLI)
2. current ThisTimeLineID, which is bumped every time a timeline-bumping
checkpoint record is replayed. (this is not currently visible to
backends, but we could easily add a shared memory variable for it)
3. curFileTLI. That is, the TLI of the current file that we're
replaying. This is usually the same as ThisTimeLineID, except when
replaying a WAL segment where the timeline changes
4. Something else?

What do you use these functions for? Which option would make the most sense?

- Heikki