On 2020/04/01 16:53, movead...@highgo.ca wrote:
But, sorry,,, I failed to understand the issue that you reported, yet....
You mean that the first call of pg_wal_replay_pause() in the step #2
should check whether the trigger file exists or not? If so, could you
tell me why we should do that?
Sorry about my pool english. The 'pg_wal_replay_pause()' is executed
in step 4. I mention it in step 2 is for explain why it need lots of insert
data.
BTW, right now only the startup process is allowed to call
CheckForStandbyTrigger(). So the backend process calling
pg_wal_replay_pause() and PromoteIsTriggered() is not allowed to call
CheckForStandbyTrigger(). The current logic is that the startup process
is responsible for checking the trigger file and set the flag in the shmem
It's here, startup process does not call CheckForStandbyTrigger() to check
the trigger file until a pg_wal_replay_pause() or PromoteIsTriggered() comes,
so first time to call the pg_wal_replay_pause(), it use a wrong
'SharedPromoteIsTriggered' value.
if promotion is triggered. Then other processes like backend know
whether promotion is ongoing or not from the shmem. So basically
the backend doesn't need to check the trigger file itself.
If backend is not allowed to call CheckForStandbyTrigger(), then you should
find a way to hold it.
In another word, during the recovery if I add the trigger file, the starup
process
do not know it at all until after a pg_wal_replay_pause() come.
Thanks for the explanation again! Maybe I understand your point.
As far as I read the code, in the standby mode, the startup process
periodically checks the trigger file in WaitForWALToBecomeAvailable().
No?
There can be small delay between the creation of the trigger file
and the periodic call to CheckForStandbyTrigger() by the startup process.
If you execute pg_wal_replay_pause() during that delay, it would suceed.
But you'd like to get rid of that delay completely? In other words,
both the startup process and the backend calling pg_wal_replay_pause()
should detect the existence of the trigger file immdiately after
it's created?
Regards,
--
Fujii Masao
NTT DATA CORPORATION
Advanced Platform Technology Group
Research and Development Headquarters
