Re: pg_xlogfile_name_offset() et al and recovery

On Thu, Jul 7, 2016 at 3:59 PM, Amit Langote
<Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> While reading the thread "BUG #14230: Wrong timeline returned by
> pg_stop_backup on a standby", I came to know that ThisTimelineId is
> invalid on standby. And because pg_xlogfile_name_offset() uses the same
> to compute its result, it makes sense to prevent it from being used on a
> standby.

To be honest, I have always found that this restriction was hard to
justify on a function that basically performs a static calculation. So
what about removing this error and use GetXLogReplayRecPtr() to fetch
the timeline ID? Per se the patch attached:
=# select * from pg_xlogfile_name_offset(pg_last_xlog_replay_location());
file_name | file_offset
--------------------------+-------------
000000010000000000000003 | 2192
(1 row)

The same applies of course to pg_xlogfile_name():
=# select pg_xlogfile_name(pg_last_xlog_replay_location());
pg_xlogfile_name
--------------------------
000000010000000000000003
(1 row)
--
Michael