On Tue, 19 Jan 2021 at 8:12 AM, Yugo NAGATA <nag...@sraoss.co.jp> wrote:
> On Sun, 17 Jan 2021 11:33:52 +0530 > Dilip Kumar <dilipbal...@gmail.com> wrote: > > > On Thu, Jan 14, 2021 at 6:49 PM Yugo NAGATA <nag...@sraoss.co.jp> wrote: > > > > > > On Wed, 13 Jan 2021 17:49:43 +0530 > > > Dilip Kumar <dilipbal...@gmail.com> wrote: > > > > > > > On Wed, Jan 13, 2021 at 3:35 PM Dilip Kumar <dilipbal...@gmail.com> > wrote: > > > > > > > > > > On Wed, Jan 13, 2021 at 3:27 PM Yugo NAGATA <nag...@sraoss.co.jp> > wrote: > > > > > > > > > > > > On Thu, 10 Dec 2020 11:25:23 +0530 > > > > > > Dilip Kumar <dilipbal...@gmail.com> wrote: > > > > > > > > > > > > > > > However, I wonder users don't expect > pg_is_wal_replay_paused to wait. > > > > > > > > > Especially, if max_standby_streaming_delay is -1, this > will be blocked forever, > > > > > > > > > although this setting may not be usual. In addition, some > users may set > > > > > > > > > recovery_min_apply_delay for a large. If such users call > pg_is_wal_replay_paused, > > > > > > > > > it could wait for a long time. > > > > > > > > > > > > > > > > > > At least, I think we need some descriptions on document to > explain > > > > > > > > > pg_is_wal_replay_paused could wait while a time. > > > > > > > > > > > > > > > > Ok > > > > > > > > > > > > > > Fixed this, added some comments in .sgml as well as in > function header > > > > > > > > > > > > Thank you for fixing this. > > > > > > > > > > > > Also, is it better to fix the description of pg_wal_replay_pause > from > > > > > > "Pauses recovery." to "Request to pause recovery." in according > with > > > > > > pg_is_wal_replay_paused? > > > > > > > > > > Okay > > > > > > > > > > > > > > > > > > > > Also, how about adding a new boolean argument to > pg_is_wal_replay_paused to > > > > > > > > > control whether this waits for recovery to get paused or > not? By setting its > > > > > > > > > default value to true or false, users can use the old > format for calling this > > > > > > > > > and the backward compatibility can be maintained. > > > > > > > > > > > > > > > > So basically, if the wait_recovery_pause flag is false then > we will > > > > > > > > immediately return true if the pause is requested? I agree > that it is > > > > > > > > good to have an API to know whether the recovery pause is > requested or > > > > > > > > not but I am not sure is it good idea to make this API serve > both the > > > > > > > > purpose? Anyone else have any thoughts on this? > > > > > > > > > > > > > > > > > > > > I think the current pg_is_wal_replay_paused() already has > another purpose; > > > > > > this waits recovery to actually get paused. If we want to limit > this API's > > > > > > purpose only to return the pause state, it seems better to fix > this to return > > > > > > the actual state at the cost of lacking the backward > compatibility. If we want > > > > > > to know whether pause is requested, we may add a new API like > > > > > > pg_is_wal_replay_paluse_requeseted(). Also, if we want to wait > recovery to actually > > > > > > get paused, we may add an option to pg_wal_replay_pause() for > this purpose. > > > > > > > > > > > > However, this might be a bikeshedding. If anyone don't care that > > > > > > pg_is_wal_replay_paused() can make user wait for a long time, I > don't care either. > > > > > > > > > > I don't think that it will be blocked ever, because > > > > > pg_wal_replay_pause is sending the WakeupRecovery() which means the > > > > > recovery process will not be stuck on waiting for the WAL. > > > > > > Yes, there is no stuck on waiting for the WAL. However, it can be > stuck during resolving > > > a recovery conflict. The process could wait for > max_standby_streaming_delay or > > > max_standby_archive_delay at most before recovery get completely > paused. > > > > Okay, I agree that it is possible so for handling this we have a > > couple of options > > 1. pg_is_wal_replay_paused(), interface will wait for recovery to > > actually get paused, but user have an option to cancel that. So I > > agree that there is currently no option to just know that recovery > > pause is requested without waiting for its actually get paused if it > > is requested. So one option is we can provide an another interface as > > you mentioned pg_is_wal_replay_paluse_requeseted(), which can just > > return the request status. I am not sure how useful it is. > > If it is acceptable that pg_is_wal_replay_paused() makes users wait, > I'm ok for the current interface. I don't feel the need of > pg_is_wal_replay_paluse_requeseted(). > > > > > 2. Pass an option to pg_is_wal_replay_paused whether to wait for > > recovery to actually get paused or not. > > > > 3. Pass an option to pg_wal_replay_pause(), whether to wait for > > recovery pause or just request and return. > > > > I like the option 1, any other opinion on this? > > > > > Also, it could wait for recovery_min_apply_delay if it has a valid > value. It is possible > > > that a user set this parameter to a large value, so it could wait for > a long time. However, > > > this will be avoided by calling recoveryPausesHere() or > CheckAndSetRecoveryPause() in > > > recoveryApplyDelay(). > > > > Right > > Is there any reason not to do it? I think I missed that.. I will do in the next version > -- Regards, Dilip Kumar EnterpriseDB: http://www.enterprisedb.com
