source-postgres: Handle NULL confirmed_flush_lsn #2436
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In normal operation a replication slot will always have a non-null `confirmed_flush_lsn`, but we saw the other day that it _is_ actually possible to observe a null value for that field if the replication slot is stuck in the middle of being created because it has to wait for a long-running transaction to complete. Since one major cause of replication slot recreation is when the old slot gets invalidated, and one major cause of invalidation is when a long-running transaction forces excessive WAL retention, this is actually less rare than it seems. It will happen any time a long-running transaction causes slot invalidation and the user just hits "Backfill All" without killing the transaction (assuming it didn't end on its own, of course). Since I would really like to make these `queryReplicationSlotInfo` checks fatal errors in the near future this logic needs to be bulletproof, so we need to handle that situation.
willdonnelly
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Description:
In normal operation a replication slot will always have a non-null
confirmed_flush_lsn, but we saw the other day that it is actually possible to observe a null value for that field if the replication slot is stuck in the middle of being created because it has to wait for a long-running transaction to complete.Since one major cause of replication slot recreation is when the old slot gets invalidated, and one major cause of invalidation is when a long-running transaction forces excessive WAL retention, this is actually less rare than it seems. It will happen any time a long-running transaction causes slot invalidation and the user just hits "Backfill All" without killing the transaction (assuming it didn't end on its own, of course).
Since I would really like to make these
queryReplicationSlotInfochecks fatal errors in the near future this logic needs to be bulletproof, so we need to handle that situation.This change is