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Prevent maintanince deamon crashes due to dead processes 

If after the distributed deadlock detection decides to cancel
a backend, the backend has been terminated/killed/cancelled
externally, we might be accessing to a NULL pointer. This commit
prevents that case by ignoring the current distributed deadlock.
pull/1612/head
Onder Kalaci 2017-08-23 13:26:05 +03:00
parent 46f81d5531
commit c7bb29b69e
1 changed files with 37 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

52
src/backend/distributed/transaction/distributed_deadlock_detection.c
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@ -50,7 +50,7 @@ static void BuildDeadlockPathList(QueuedTransactionNode *cycledTransactionNode,
TransactionNode **transactionNodeStack, TransactionNode **transactionNodeStack,
List **deadlockPath); List **deadlockPath);
static void ResetVisitedFields(HTAB *adjacencyList); static void ResetVisitedFields(HTAB *adjacencyList);
static void AssociateDistributedTransactionWithBackendProc(TransactionNode * static bool AssociateDistributedTransactionWithBackendProc(TransactionNode *
transactionNode); transactionNode);
static TransactionNode * GetOrCreateTransactionNode(HTAB *adjacencyList, static TransactionNode * GetOrCreateTransactionNode(HTAB *adjacencyList,
DistributedTransactionId * DistributedTransactionId *
@ -149,7 +149,7 @@ CheckForDistributedDeadlocks(void)
&deadlockPath); &deadlockPath);
if (deadlockFound) if (deadlockFound)
{ {
TransactionNode *youngestTransaction = transactionNode; TransactionNode *youngestAliveTransaction = NULL;
ListCell *participantTransactionCell = NULL; ListCell *participantTransactionCell = NULL;
/* /*
@ -175,34 +175,45 @@ CheckForDistributedDeadlocks(void)
{ {
TransactionNode *currentNode = TransactionNode *currentNode =
(TransactionNode *) lfirst(participantTransactionCell); (TransactionNode *) lfirst(participantTransactionCell);
bool transactionAssociatedWithProc =
TimestampTz youngestTimestamp =
youngestTransaction->transactionId.timestamp;
TimestampTz currentTimestamp = currentNode->transactionId.timestamp;
AssociateDistributedTransactionWithBackendProc(currentNode); AssociateDistributedTransactionWithBackendProc(currentNode);
TimestampTz youngestTimestamp = 0;
TimestampTz currentTimestamp = 0;
LogTransactionNode(currentNode); LogTransactionNode(currentNode);
if (currentNode->transactionId.initiatorNodeIdentifier == /* we couldn't find the backend process originated the transaction */
GetLocalGroupId() && if (!transactionAssociatedWithProc)
timestamptz_cmp_internal(currentTimestamp, youngestTimestamp) == 1)
{ {
youngestTransaction = currentNode; continue;
}
if (youngestAliveTransaction == NULL)
{
youngestAliveTransaction = currentNode;
continue;
}
youngestTimestamp = youngestAliveTransaction->transactionId.timestamp;
currentTimestamp = currentNode->transactionId.timestamp;
if (timestamptz_cmp_internal(currentTimestamp, youngestTimestamp) == 1)
{
youngestAliveTransaction = currentNode;
} }
} }
/* we should find the backend */ /* we found the deadlock and its associated proc exists */
Assert(youngestTransaction->initiatorProc != NULL); if (youngestAliveTransaction)
{
CancelTransactionDueToDeadlock(youngestTransaction->initiatorProc); CancelTransactionDueToDeadlock(youngestAliveTransaction->initiatorProc);
LogCancellingBackend(youngestTransaction); LogCancellingBackend(youngestAliveTransaction);
hash_seq_term(&status); hash_seq_term(&status);
return true; return true;
} }
} }
}
return false; return false;
} }
@ -349,8 +360,11 @@ ResetVisitedFields(HTAB *adjacencyList)
* *
* The function goes over all the backends, checks for the backend with * The function goes over all the backends, checks for the backend with
* the same transaction number as the given transaction node. * the same transaction number as the given transaction node.
*
* If the transaction cannot be associated with a backend process, the function
* returns false. Otherwise, the function returns true.
*/ */
static void static bool
AssociateDistributedTransactionWithBackendProc(TransactionNode *transactionNode) AssociateDistributedTransactionWithBackendProc(TransactionNode *transactionNode)
{ {
int backendIndex = 0; int backendIndex = 0;
@ -394,8 +408,10 @@ AssociateDistributedTransactionWithBackendProc(TransactionNode *transactionNode)
transactionNode->initiatorProc = currentProc; transactionNode->initiatorProc = currentProc;
break; return true;
} }
return false;
} }