Initial attempt at fixing deadlock detection

The deadlock detector had a bug where it would detect deadlocks even
when there were none. This could happen when the lock graph contains a
combination of transactions had a distributed transaction id assigned,
but also some transactions that did not.

Multiple different transactions without a transaction id were considered
the same transaction (with transaction id 0). Thus a cycle would be
instantly detected if two were waiting on eachother. However, due to the
nature of the deadlock detector these transaction without distributed
transaction ids would normally not be included in the lock graph at all.
Only when a transaction that has a distributed transaction id was
waiting on one without, would it be included.

src/backend/distributed/transaction/distributed_deadlock_detection.c

@@ -458,24 +458,26 @@ BuildAdjacencyListsForWaitGraph(WaitGraph *waitGraph)
 
 	HTAB *adjacencyList = hash_create("distributed deadlock detection", 64, &info,
 									  hashFlags);
-
 	for (int edgeIndex = 0; edgeIndex < edgeCount; edgeIndex++)
 	{
 		WaitEdge *edge = &waitGraph->edges[edgeIndex];
 		bool transactionOriginator = false;
 
+
 		DistributedTransactionId waitingId = {
 			edge->waitingNodeId,
 			transactionOriginator,
 			edge->waitingTransactionNum,
-			edge->waitingTransactionStamp
+			edge->waitingTransactionStamp,
+			edge->waitingGPid,
 		};
 
 		DistributedTransactionId blockingId = {
 			edge->blockingNodeId,
 			transactionOriginator,
 			edge->blockingTransactionNum,
-			edge->blockingTransactionStamp
+			edge->blockingTransactionStamp,
+			edge->blockingGPid,
 		};
 
 		TransactionNode *waitingTransaction =
@@ -529,6 +531,8 @@ DistributedTransactionIdHash(const void *key, Size keysize)
 									   sizeof(int64)));
 	hash = hash_combine(hash, hash_any((unsigned char *) &entry->timestamp,
 									   sizeof(TimestampTz)));
+	hash = hash_combine(hash, hash_any((unsigned char *) &entry->gpid,
+									   sizeof(uint64)));
 
 	return hash;
 }
@@ -547,7 +551,15 @@ DistributedTransactionIdCompare(const void *a, const void *b, Size keysize)
 	DistributedTransactionId *xactIdA = (DistributedTransactionId *) a;
 	DistributedTransactionId *xactIdB = (DistributedTransactionId *) b;
 
-	if (!TimestampDifferenceExceeds(xactIdB->timestamp, xactIdA->timestamp, 0))
+	if (xactIdA->gpid < xactIdB->gpid)
+	{
+		return -1;
+	}
+	else if (xactIdA->gpid < xactIdB->gpid)
+	{
+		return 1;
+	}
+	else if (!TimestampDifferenceExceeds(xactIdB->timestamp, xactIdA->timestamp, 0))
 	{
 		/* ! (B <= A) = A < B */
 		return -1;
@@ -595,11 +607,13 @@ LogCancellingBackend(TransactionNode *transactionNode)
 
 	StringInfo logMessage = makeStringInfo();
 
-	appendStringInfo(logMessage, "Cancelling the following backend "
-								 "to resolve distributed deadlock "
-								 "(transaction number = " UINT64_FORMAT ", pid = %d)",
+	appendStringInfo(logMessage,
+					 "Cancelling the following backend "
+					 "to resolve distributed deadlock "
+					 "(transaction number = " UINT64_FORMAT
+					 ", gpid = " UINT64_FORMAT ")",
 					 transactionNode->transactionId.transactionNumber,
-					 transactionNode->initiatorProc->pid);
+					 transactionNode->transactionId.gpid);
 
 	LogDistributedDeadlockDebugMessage(logMessage->data);
 }
@@ -621,12 +635,14 @@ LogTransactionNode(TransactionNode *transactionNode)
 	DistributedTransactionId *transactionId = &(transactionNode->transactionId);
 
 	appendStringInfo(logMessage,
-					 "[DistributedTransactionId: (%d, " UINT64_FORMAT ", %s)] = ",
+					 "[DistributedTransactionId: (" UINT64_FORMAT ", %d," UINT64_FORMAT
+					 ", %s)] = ",
+					 transactionId->gpid,
 					 transactionId->initiatorNodeIdentifier,
 					 transactionId->transactionNumber,
 					 timestamptz_to_str(transactionId->timestamp));
 
-	appendStringInfo(logMessage, "[WaitsFor transaction numbers: %s]",
+	appendStringInfo(logMessage, "[WaitsFor gpids: %s]",
 					 WaitsForToString(transactionNode->waitsFor));
 
 	/* log the backend query if the proc is associated with the transaction */
@@ -680,7 +696,7 @@ WaitsForToString(List *waitsFor)
 		}
 
 		appendStringInfo(transactionIdStr, UINT64_FORMAT,
-						 waitingNode->transactionId.transactionNumber);
+						 waitingNode->transactionId.gpid);
 	}
 
 	return transactionIdStr->data;

src/include/distributed/transaction_identifier.h

@@ -36,6 +36,7 @@ typedef struct DistributedTransactionId
 	bool transactionOriginator;
 	uint64 transactionNumber;
 	TimestampTz timestamp;
+	uint64 gpid;
 } DistributedTransactionId;
 
 

src/test/regress/create_schedule

@@ -1,8 +1,7 @@
-test: intermediate_result_pruning_create prepared_statements_create_load ch_benchmarks_create_load dropped_columns_create_load distributed_planning_create_load local_dist_join_load nested_execution_create partitioned_indexes_create
+test: intermediate_result_pruning_create prepared_statements_create_load ch_benchmarks_create_load dropped_columns_create_load distributed_planning_create_load local_dist_join_load nested_execution_create partitioned_indexes_create sequences_create
 test: connectivity_checks
 test: schemas_create
 test: views_create
-test: sequences_create
 test: index_create
 test: function_create
 test: arbitrary_configs_truncate_create