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Fix snapshot handling in logicalmsg_decode

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Whe decoding a transactional logical message, logicalmsg_decode called
SnapBuildGetOrBuildSnapshot. But we may not have a consistent snapshot
yet at that point. We don't actually need the snapshot in this case
(during replay we'll have the snapshot from the transaction), so in
practice this is harmless. But in assert-enabled build this crashes.

Fixed by requesting the snapshot only in non-transactional case, where
we are guaranteed to have SNAPBUILD_CONSISTENT.

Backpatch to 11. The issue exists since 9.6.

Backpatch-through: 11
Reviewed-by: Andres Freund
Discussion: https://postgr.es/m/84d60912-6eab-9b84-5de3-41765a5449e8@enterprisedb.com
This commit is contained in:
Tomas Vondra
2023-02-22 15:24:09 +01:00
parent 576b25bfd0
commit 949ac32e12
2 changed files with 22 additions and 2 deletions
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10
src/backend/replication/logical/reorderbuffer.c
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@ -828,6 +828,13 @@ ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid,
Assert(xid != InvalidTransactionId);
/*
* We don't expect snapshots for transactional changes - we'll use the
* snapshot derived later during apply (unless the change gets
* skipped).
*/
Assert(!snapshot);
oldcontext = MemoryContextSwitchTo(rb->context);
change = ReorderBufferGetChange(rb);
@ -846,6 +853,9 @@ ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid,
ReorderBufferTXN *txn = NULL;
volatile Snapshot snapshot_now = snapshot;
/* Non-transactional changes require a valid snapshot. */
Assert(snapshot_now);
if (xid != InvalidTransactionId)
txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);