Fix GetNewTransactionId()'s interaction with xidVacLimit.

macdice · macdice · commit f7feb020c3d8 · 2019-04-12T16:47:50.000+12:00
Commit ad30805 switched to returning a FullTransactionId, but failed to load the potentially updated value in the case where xidVacLimit is reached and we release and reacquire the lock. Repair, closing bug #15727. While reviewing that commit, also fix the size computation used by EstimateTransactionStateSize() and switch to the mul_size() macro traditionally used in such expressions. Author: Thomas Munro Reported-by: Roman Zharkov Discussion: https://postgr.es/m/15727-0be246e7d852d229%40postgresql.org
diff --git a/src/backend/access/transam/varsup.c b/src/backend/access/transam/varsup.c
@@ -159,7 +159,8 @@ GetNewTransactionId(bool isSubXact)
 
 		/* Re-acquire lock and start over */
 		LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
-		xid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);
+		full_xid = ShmemVariableCache->nextFullXid;
+		xid = XidFromFullTransactionId(full_xid);
 	}
 
 	/*
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
@@ -5151,7 +5151,7 @@ EstimateTransactionStateSpace(void)
 		nxids = add_size(nxids, s->nChildXids);
 	}
 
-	return add_size(size, sizeof(SerializedTransactionState) * nxids);
+	return add_size(size, mul_size(sizeof(TransactionId), nxids));
 }
 
 /*

Original file line number	Diff line number	Diff line change
`@@ -159,7 +159,8 @@ GetNewTransactionId(bool isSubXact)`
`159`	`159`
`160`	`160`	`/* Re-acquire lock and start over */`
`161`	`161`	`LWLockAcquire(XidGenLock, LW_EXCLUSIVE);`
`162`		`- xid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);`
	`162`	`+ full_xid = ShmemVariableCache->nextFullXid;`
	`163`	`+ xid = XidFromFullTransactionId(full_xid);`
`163`	`164`	`}`
`164`	`165`
`165`	`166`	`/*`
Original file line number	Diff line number	Diff line change
`@@ -5151,7 +5151,7 @@ EstimateTransactionStateSpace(void)`
`5151`	`5151`	`nxids = add_size(nxids, s->nChildXids);`
`5152`	`5152`	`}`
`5153`	`5153`
`5154`		`- return add_size(size, sizeof(SerializedTransactionState) * nxids);`
	`5154`	`+ return add_size(size, mul_size(sizeof(TransactionId), nxids));`
`5155`	`5155`	`}`
`5156`	`5156`
`5157`	`5157`	`/*`