From 7aa4fb592530b74bf05f62c52b736ee3910691b9 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Fri, 12 Jun 2020 10:44:32 +1200 Subject: Improve comments for [Heap]CheckForSerializableConflictOut(). Rewrite the documentation of these functions, in light of recent bug fix commit 5940ffb2. Back-patch to 13 where the check-for-conflict-out code was split up into AM-specific and generic parts, and new documentation was added that now looked wrong. Reviewed-by: Peter Geoghegan Discussion: https://postgr.es/m/db7b729d-0226-d162-a126-8a8ab2dc4443%40jepsen.io --- src/backend/storage/lmgr/predicate.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) (limited to 'src/backend/storage/lmgr/predicate.c') diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c index ba93fb199d4..d24919f76b6 100644 --- a/src/backend/storage/lmgr/predicate.c +++ b/src/backend/storage/lmgr/predicate.c @@ -4037,13 +4037,16 @@ CheckForSerializableConflictOutNeeded(Relation relation, Snapshot snapshot) /* * CheckForSerializableConflictOut - * A table AM is reading a tuple that has been modified. After determining - * that it is visible to us, it should call this function with the top - * level xid of the writing transaction. + * A table AM is reading a tuple that has been modified. If it determines + * that the tuple version it is reading is not visible to us, it should + * pass in the top level xid of the transaction that created it. + * Otherwise, if it determines that it is visible to us but it has been + * deleted or there is a newer version available due to an update, it + * should pass in the top level xid of the modifying transaction. * - * This function will check for overlap with our own transaction. If the - * transactions overlap (i.e., they cannot see each other's writes), then we - * have a conflict out. + * This function will check for overlap with our own transaction. If the given + * xid is also serializable and the transactions overlap (i.e., they cannot see + * each other's writes), then we have a conflict out. */ void CheckForSerializableConflictOut(Relation relation, TransactionId xid, Snapshot snapshot) -- cgit v1.2.3