On Sun, Jan 29, 2023 at 9:15 PM Masahiko Sawada <sawada.m...@gmail.com> wrote: > > On Sat, Jan 28, 2023 at 11:54 PM Hayato Kuroda (Fujitsu) > <kuroda.hay...@fujitsu.com> wrote: > > > > Dear Amit, Sawada-san, > > > > I have also reproduced the failure on PG15 with some debug log, and I > > agreed that > > somebody changed procArray->replication_slot_xmin to InvalidTransactionId. > > > > > > The same assertion failure has been reported on another thread[1]. > > > > Since I could reproduce this issue several times in my environment > > > > I've investigated the root cause. > > > > > > > > I think there is a race condition of updating > > > > procArray->replication_slot_xmin by CreateInitDecodingContext() and > > > > LogicalConfirmReceivedLocation(). > > > > > > > > What I observed in the test was that a walsender process called: > > > > SnapBuildProcessRunningXacts() > > > > LogicalIncreaseXminForSlot() > > > > LogicalConfirmReceivedLocation() > > > > ReplicationSlotsComputeRequiredXmin(false). > > > > > > > > In ReplicationSlotsComputeRequiredXmin() it acquired the > > > > ReplicationSlotControlLock and got 0 as the minimum xmin since there > > > > was no wal sender having effective_xmin. > > > > > > > > > > What about the current walsender process which is processing > > > running_xacts via SnapBuildProcessRunningXacts()? Isn't that walsender > > > slot's effective_xmin have a non-zero value? If not, then why? > > > > Normal walsenders which are not for tablesync create a replication slot with > > NOEXPORT_SNAPSHOT option. I think in this case, CreateInitDecodingContext() > > is > > called with need_full_snapshot = false, and slot->effective_xmin is not > > updated. > > Right. This is how we create a slot used by an apply worker. >
I was thinking about how that led to this problem because GetOldestSafeDecodingTransactionId() ignores InvalidTransactionId. It seems that is possible when both builder->xmin and replication_slot_catalog_xmin precede replication_slot_catalog_xmin. Do you see any different reason for it? -- With Regards, Amit Kapila.
