On Tue, Dec 17, 2024 at 8:54 AM Zhijie Hou (Fujitsu) <houzj.f...@fujitsu.com> wrote: > > On Monday, December 16, 2024 7:21 PM Dilip Kumar <dilipbal...@gmail.com> > wrote: > > > So IIUC in step 2) we send the message and get the list of all the > > transactions which are in the commit phase? What do you exactly mean by a > > transaction which is in the commit phase? > > I was referring to transactions calling RecordTransactionCommit() and have > entered the commit critical section. In the patch, we checked if the proc has > marked the new flag DELAY_CHKPT_IN_COMMIT in 'MyProc->delayChkptFlags'. > > > Can I assume transactions which are currently running on the publisher? > > I think it's a subset of the running transactions. We only get the > transactions > in commit phase with the intention to avoid delays caused by waiting for > long-running transactions to complete, which can result in the long retention > of dead tuples.
Ok > We decided to wait for running(committing) transactions due to the WAL/LSN > inversion issue[1]. The original idea is to directly return the latest WAL > write position without checking running transactions. But since there is a gap > between when we acquire the commit_timestamp and the commit LSN, it's possible > the transactions might have been assigned an earlier commit timestamp but have > not yet written the commit WAL record. Yes, that makes sense. > > And in step 3) we wait for all the transactions to get committed which we > > saw > > running (or in the commit phase) and we anyway don't worry about the newly > > started transactions as they would not be problematic for us. And in step 4) > > we would wait for all the flush location to reach "last received WAL > > position", here my question is what exactly will be the "last received WAL > > position" I assume it would be the position somewhere after the position of > > the commit WAL of all the transaction we were interested on the publisher? > > Yes, your understanding is correct. It's a position after the position of all > the interesting transactions. In the patch, we get the latest WAL write > position(GetXLogWriteRecPtr()) in walsender after all interesting transactions > have finished and reply it to apply worker. Got it, thanks. -- Regards, Dilip Kumar EnterpriseDB: http://www.enterprisedb.com
