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-rw-r--r--src/backend/executor/nodeModifyTable.c46
1 files changed, 38 insertions, 8 deletions
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 6fea82e..1ad5dcb 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -2947,8 +2947,29 @@ lmerge_matched:;
case TM_SelfModified:
/*
- * The SQL standard disallows this for MERGE.
+ * The target tuple was already updated or deleted by the
+ * current command, or by a later command in the current
+ * transaction. The former case is explicitly disallowed by
+ * the SQL standard for MERGE, which insists that the MERGE
+ * join condition should not join a target row to more than
+ * one source row.
+ *
+ * The latter case arises if the tuple is modified by a
+ * command in a BEFORE trigger, or perhaps by a command in a
+ * volatile function used in the query. In such situations we
+ * should not ignore the MERGE action, but it is equally
+ * unsafe to proceed. We don't want to discard the original
+ * MERGE action while keeping the triggered actions based on
+ * it; and it would be no better to allow the original MERGE
+ * action while discarding the updates that it triggered. So
+ * throwing an error is the only safe course.
*/
+ if (context->tmfd.cmax != estate->es_output_cid)
+ ereport(ERROR,
+ (errcode(ERRCODE_TRIGGERED_DATA_CHANGE_VIOLATION),
+ errmsg("tuple to be updated or deleted was already modified by an operation triggered by the current command"),
+ errhint("Consider using an AFTER trigger instead of a BEFORE trigger to propagate changes to other rows.")));
+
if (TransactionIdIsCurrentTransactionId(context->tmfd.xmax))
ereport(ERROR,
(errcode(ERRCODE_CARDINALITY_VIOLATION),
@@ -2956,6 +2977,7 @@ lmerge_matched:;
errmsg("%s command cannot affect row a second time",
"MERGE"),
errhint("Ensure that not more than one source row matches any one target row.")));
+
/* This shouldn't happen */
elog(ERROR, "attempted to update or delete invisible tuple");
break;
@@ -3064,19 +3086,27 @@ lmerge_matched:;
/*
* This can be reached when following an update
* chain from a tuple updated by another session,
- * reaching a tuple that was already updated in
- * this transaction. If previously modified by
- * this command, ignore the redundant update,
- * otherwise error out.
- *
- * See also response to TM_SelfModified in
- * ExecUpdate().
+ * reaching a tuple that was already updated or
+ * deleted by the current command, or by a later
+ * command in the current transaction. As above,
+ * this should always be treated as an error.
*/
if (context->tmfd.cmax != estate->es_output_cid)
ereport(ERROR,
(errcode(ERRCODE_TRIGGERED_DATA_CHANGE_VIOLATION),
errmsg("tuple to be updated or deleted was already modified by an operation triggered by the current command"),
errhint("Consider using an AFTER trigger instead of a BEFORE trigger to propagate changes to other rows.")));
+
+ if (TransactionIdIsCurrentTransactionId(context->tmfd.xmax))
+ ereport(ERROR,
+ (errcode(ERRCODE_CARDINALITY_VIOLATION),
+ /* translator: %s is a SQL command name */
+ errmsg("%s command cannot affect row a second time",
+ "MERGE"),
+ errhint("Ensure that not more than one source row matches any one target row.")));
+
+ /* This shouldn't happen */
+ elog(ERROR, "attempted to update or delete invisible tuple");
return false;
default: