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Commit7aa4fb5

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Improve comments for [Heap]CheckForSerializableConflictOut().
Rewrite the documentation of these functions, in light of recent bug fixcommit5940ffb.Back-patch to 13 where the check-for-conflict-out code was split up intoAM-specific and generic parts, and new documentation was added that nowlooked wrong.Reviewed-by: Peter Geoghegan <pg@bowt.ie>Discussion:https://postgr.es/m/db7b729d-0226-d162-a126-8a8ab2dc4443%40jepsen.io
1 parent59fa7eb commit7aa4fb5

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‎src/backend/access/heap/heapam.c

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@@ -8975,15 +8975,13 @@ heap_mask(char *pagedata, BlockNumber blkno)
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/*
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* HeapCheckForSerializableConflictOut
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*We are reading a tuple which has been modified. If it is visible to
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*us but has been deleted, that indicates a rw-conflict out. If it's
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*not visible and was created by a concurrent (overlapping)
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*serializable transaction, that is also a rw-conflict out,
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*We are reading a tuple. If it's not visible, there may be a
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*rw-conflict out with the inserter. Otherwise, if it is visible to us
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*but has been deleted, there may be a rw-conflict out with the deleter.
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*
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* We will determine the top level xid of the writing transaction with which
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* we may be in conflict, and check for overlap with our own transaction.
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* If the transactions overlap (i.e., they cannot see each other's writes),
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* then we have a conflict out.
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* we may be in conflict, and ask CheckForSerializableConflictOut() to check
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* for overlap with our own transaction.
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*
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* This function should be called just about anywhere in heapam.c where a
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* tuple has been read. The caller must hold at least a shared lock on the

‎src/backend/storage/lmgr/predicate.c

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Original file line numberDiff line numberDiff line change
@@ -4037,13 +4037,16 @@ CheckForSerializableConflictOutNeeded(Relation relation, Snapshot snapshot)
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/*
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* CheckForSerializableConflictOut
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*A table AM is reading a tuple that has been modified. After determining
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*that it is visible to us, it should call this function with the top
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*level xid of the writing transaction.
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*A table AM is reading a tuple that has been modified. If it determines
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*that the tuple version it is reading is not visible to us, it should
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*pass in the top level xid of the transaction that created it.
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*Otherwise, if it determines that it is visible to us but it has been
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*deleted or there is a newer version available due to an update, it
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*should pass in the top level xid of the modifying transaction.
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*
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* This function will check for overlap with our own transaction. If the
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* transactions overlap (i.e., they cannot see each other's writes), then we
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* have a conflict out.
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* This function will check for overlap with our own transaction. If the given
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*xid is also serializable and thetransactions overlap (i.e., they cannot see
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*each other's writes), then wehave a conflict out.
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*/
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void
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CheckForSerializableConflictOut(Relationrelation,TransactionIdxid,Snapshotsnapshot)

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