On Sat, May 15, 2021 at 12:37 PM 刘鹏程 <pengcheng...@tju.edu.cn> wrote: > > > BTW, I test it in a high performance server. It is verly easily be > reproduced. My colleague and me use different environment both can reproduce > it. >
Hi Pengcheng, Although the issue won't reproduce easily in my system, I can certainly see how, for the snapshots used in the parallel worker case, the Active snapshot used is potentially an earlier snapshot that the Transaction snapshot. I don't know why it is getting a newer Transaction snapshot in InitializeParallelDSM(), when it has previously pushed the return value of GetTransactionSnapshot() as the Active snapshot. So I too hope Tom or Robert can explain what is going on here and how to resolve it (as you requested them to, in your other post). I actually think that the Assert in SubTransGetTopmostTransaction() is correct, but in the parallel-worker case, the snapshots are not being setup correctly. Can you try the trivial change below and see if it prevents the coredump? Regards, Greg Nancarrow Fujitsu Australia diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c index 14a8690019..870889053f 100644 --- a/src/backend/access/transam/parallel.c +++ b/src/backend/access/transam/parallel.c @@ -216,7 +216,7 @@ InitializeParallelDSM(ParallelContext *pcxt) int i; FixedParallelState *fps; dsm_handle session_dsm_handle = DSM_HANDLE_INVALID; - Snapshot transaction_snapshot = GetTransactionSnapshot(); + Snapshot transaction_snapshot = GetActiveSnapshot(); Snapshot active_snapshot = GetActiveSnapshot(); /* We might be running in a very short-lived memory context. */
