On Tue, Mar 2, 2021 at 7:54 PM Amul Sul <sula...@gmail.com> wrote: > XLogAcceptWrites() tried to club all the WAL write operations that happen at > the > end of StartupXLOG(). The only exception is that promotion checkpoint.
Okay, I was expecting that XLogAcceptWrites should have all the WAL write-related operations which should either executed at the end of StartupXLOG() if the system is not read-only or after the system is set back to read-write. But promotion-related code is completely irrelevant when it is executed from PerformPendingStartupOperations. So I am not entirely sure that whether we want to keep those stuff in XLogAcceptWrites. > > That will look cleaner. > > I think it would be better to move the promotion checkpoint call inside > XLogAcceptWrites() as well. So that we can say XLogAcceptWrites() is a part of > StartupXLOG() does the required WAL writes. Thoughts? Okay so if we want to keep all the WAL write inside XLogAcceptWrites including promotion-related stuff then +1 for moving this also inside XLogAcceptWrites. > > > > > > 1] > > > http://postgr.es/m/CA+TgmoZ=cctbaxxmtyzogxegqzoz9smkbwrdpsacpjvfcgc...@mail.gmail.com > > > 2] > > > http://postgr.es/m/caaj_b97xx-nqrym_uxzecph9asgomrordnhrg1n51fdcdwo...@mail.gmail.com > > > > 2. > > I did not clearly understand your concern in point [2], because of > > which you have to postpone RECOVERY_STATE_DONE untill system is set > > back to read-write. Can you explain this? > > > > Sure, for that let me explain how this transition to read-write occurs. When > a > backend executes a function (ie. pg_prohibit_wal(false)) to make the system > read-write then that system state changes will be conveyed by the Checkpointer > process to all existing backends using global barrier and while Checkpointer > in > the progress of conveying this barrier, any existing backends who might have > absorbed barriers can write new records. > > We don't want that to happen in cases where previous recovery-end-checkpoint > is > skipped in startup. We want Checkpointer first to convey the barrier to all > backends but, the backend shouldn't write wal until the Checkpointer writes > recovery-end-checkpoint record. > > To refrain these backends from writing WAL I think we should keep the server > in > crash recovery mode until UpdateFullPageWrites(), > end-of-recovery-checkpoint, and XLogReportParameters() are performed. Thanks for the explanation. Now, I understand the problem, however, I am not sure that whether keeping the system in recovery is the best way to solve this but as of now I don't have anything better to suggest, and immediately I couldn’t think of any problem with this solution. But I will think about this again. -- Regards, Dilip Kumar EnterpriseDB: http://www.enterprisedb.com
