Re: Can there ever be out of sequence WAL files?
On Tue, Dec 28, 2021 at 7:45 AM Bharath Rupireddy wrote: > > Hi, > > Can the postgres server ever have/generate out of sequence WAL files? > For instance, 0001020C00A2, 0001020C00A3, > 0001020C00A5 and so on, missing 0001020C00A4. > Manual/Accidental deletion of the WAL files can happes, but are there > any other extreme situations (like recycling, removing old WAL files > etc.) caused by the postgres server leading to missing WAL files? > > What happens when postgres server finds missing WAL file during > crash/standby recovery? > > Thoughts? Hi Hackers, a gentle ping for the above question. I think I sent it earlier during the holiday season. Regards, Bharath Rupireddy.
Re: Can there ever be out of sequence WAL files?
On Wed, Jan 12, 2022 at 07:19:48AM +0530, Bharath Rupireddy wrote: > > > > Can the postgres server ever have/generate out of sequence WAL files? > > For instance, 0001020C00A2, 0001020C00A3, > > 0001020C00A5 and so on, missing 0001020C00A4. > > Manual/Accidental deletion of the WAL files can happes, but are there > > any other extreme situations (like recycling, removing old WAL files > > etc.) caused by the postgres server leading to missing WAL files? By definition there shouldn't be such situation, as it would otherwise be a (critical) bug. > > What happens when postgres server finds missing WAL file during > > crash/standby recovery? The recovery should fail.
Re: Can there ever be out of sequence WAL files?
On Wed, Jan 12, 2022 at 10:18:11AM +0800, Julien Rouhaud wrote: > On Wed, Jan 12, 2022 at 07:19:48AM +0530, Bharath Rupireddy wrote: >>> Can the postgres server ever have/generate out of sequence WAL files? >>> For instance, 0001020C00A2, 0001020C00A3, >>> 0001020C00A5 and so on, missing 0001020C00A4. >>> Manual/Accidental deletion of the WAL files can happes, but are there >>> any other extreme situations (like recycling, removing old WAL files >>> etc.) caused by the postgres server leading to missing WAL files? > > By definition there shouldn't be such situation, as it would otherwise be a > (critical) bug. I have seen that in the past, in cases where a system got harshly deplugged then replugged where a segment file flush got missing. But that was just a flacky system, Postgres relied just on something wrong. So the answer is that this should not happen. >>> What happens when postgres server finds missing WAL file during >>> crash/standby recovery? > > The recovery should fail. xlog.c can be a good read to check the assumptions WAL replay relies on, with things like CheckRecoveryConsistency() or reachedConsistency. -- Michael signature.asc Description: PGP signature
Re: Can there ever be out of sequence WAL files?
On Wed, Jan 12, 2022 at 01:10:25PM +0900, Michael Paquier wrote: > > xlog.c can be a good read to check the assumptions WAL replay relies > on, with things like CheckRecoveryConsistency() or > reachedConsistency. That should only stand for a WAL expected to be missing right? For something unexpected it should fail in XLogReadRecord() when trying to fetch a missing block?
Re: Can there ever be out of sequence WAL files?
On Wed, Jan 12, 2022 at 12:23:00PM +0800, Julien Rouhaud wrote: > On Wed, Jan 12, 2022 at 01:10:25PM +0900, Michael Paquier wrote: >> xlog.c can be a good read to check the assumptions WAL replay relies >> on, with things like CheckRecoveryConsistency() or >> reachedConsistency. > > That should only stand for a WAL expected to be missing right? For something > unexpected it should fail in XLogReadRecord() when trying to fetch a missing > block? Sure, as well as there are sanity checks related to invalid page references when it comes to the consistency checks. -- Michael signature.asc Description: PGP signature
