On Fri, Dec 3, 2021 at 5:00 PM Simon Riggs <simon.ri...@enterprisedb.com> wrote: > > On Fri, 3 Dec 2021 at 01:27, Dilip Kumar <dilipbal...@gmail.com> wrote: > > > > On review, I think it is also possible that we update subtrans ONLY if > > > someone uses >PGPROC_MAX_CACHED_SUBXIDS. > > > This would make subtrans much smaller and avoid one-entry-per-page > > > which is a major source of cacheing. > > > This would means some light changes in GetSnapshotData(). > > > Let me know if that seems interesting also? > > > > Do you mean to say avoid setting the sub-transactions parent if the > > number of sun-transactions is not crossing PGPROC_MAX_CACHED_SUBXIDS? > > But the TransactionIdDidCommit(), might need to fetch the parent if > > the transaction status is TRANSACTION_STATUS_SUB_COMMITTED, so how > > would we handle that? > > TRANSACTION_STATUS_SUB_COMMITTED is set as a transient state during > final commit. > In that case, the top-level xid is still in procarray when nsubxids < > PGPROC_MAX_CACHED_SUBXIDS > so we need not consult pg_subtrans in that case, see step 4 of. > TransactionIdIsInProgress()
Okay I see, that there is a rule that before calling TransactionIdDidCommit(), we must consult TransactionIdIsInProgress() for non MVCC snapshot or XidInMVCCSnapshot(). Okay so now I don't have this concern, thanks for clarifying. I will think more about this approach from other aspects. -- Regards, Dilip Kumar EnterpriseDB: http://www.enterprisedb.com
