On Tue, Apr 27, 2021 at 11:43 AM Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Mon, Apr 26, 2021 at 7:52 PM Dilip Kumar <dilipbal...@gmail.com> wrote: > > > > On Mon, Apr 26, 2021 at 6:59 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > > > > > On Mon, Apr 26, 2021 at 5:55 PM Dilip Kumar <dilipbal...@gmail.com> wrote: > > > > > > > > I am able to reproduce this and I think I have done the initial > > > > investigation. > > > > > > > > The cause of the issue is that, this transaction has only one change > > > > and that change is XLOG_HEAP2_NEW_CID, which is added through > > > > SnapBuildProcessNewCid. Basically, when we add any changes through > > > > SnapBuildProcessChange we set the base snapshot but when we add > > > > SnapBuildProcessNewCid this we don't set the base snapshot, because > > > > there is nothing to be done for this change. Now, this transaction is > > > > identified as the biggest transaction with non -partial changes, and > > > > now in ReorderBufferStreamTXN, it will return immediately because the > > > > base_snapshot is NULL. > > > > > > > > > > Your analysis sounds correct to me. > > > > > > > Thanks, I have attached a patch to fix this. > > > > Can't we use 'txns_by_base_snapshot_lsn' list for this purpose? It is > ensured in ReorderBufferSetBaseSnapshot that we always assign > base_snapshot to a top-level transaction if the current is a known > subxact. I think that will be true because we always form xid-subxid > relation before processing each record in > LogicalDecodingProcessRecord.
Yeah, we can do that, but here we are only interested in top transactions and this list will give us sub-transaction as well so we will have to skip it in the below if condition. So I think using toplevel_by_lsn and skipping the txn without base_snapshot in below if condition will be cheaper compared to process all the transactions with base snapshot i.e. txns_by_base_snapshot_lsn and skipping the sub-transactions in the below if conditions. Whats your thoughts on this? > Few other minor comments: > 1. I think we can update the comments atop function > ReorderBufferLargestTopTXN. > 2. minor typo in comments atop ReorderBufferLargestTopTXN "...There is > a scope of optimization here such that we can select the largest > transaction which has complete changes...". In this 'complete' should > be incomplete. This is not related to this patch but I think we can > fix it along with this because anyway we are going to change > surrounding comments. I will work on these in the next version. -- Regards, Dilip Kumar EnterpriseDB: http://www.enterprisedb.com
