Fix walsender to exit promptly if client requests shutdown.
It's possible for WalSndWaitForWal to be asked to wait for WAL that doesn't
exist yet. That's fine, in fact it's the normal situation if we're caught
up; but when the client requests shutdown we should not keep waiting.
The previous coding could wait indefinitely if the source server was idle.
In passing, improve the rather weak comments in this area, and slightly
rearrange some related code for better readability.
Back-patch to 9.4 where this code was introduced.
Discussion: https://postgr.es/m/14154.1498781234@sss.pgh.pa.us
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/fca85f8ef157d4d58dea1fdc8e1f1f957b74ee78
Modified Files
--------------
src/backend/replication/walsender.c | 48 ++++++++++++++++++++++++-------------
1 file changed, 31 insertions(+), 17 deletions(-)
