On Mon, 2010-08-30 at 09:59 +0300, Heikki Linnakangas wrote:
> However, is it safe to use GetOldestXMin() during recovery? Or to put it
> other way, is GetOldestXMin() functioning correctly during hot standby?
> It only scans through the ProcArray, but not the known-assigned xids
> array. That seems like an oversight that needs to be fixed.
Patch to implement that attached.
This is necessary since CreateCheckpoint is called during end of
recovery, though at that point there are still xids in KnownAssignedXids
since they aren't removed until slightly later. Not hugely important.
Also allows GetOldestXmin to be safely called elsewhere, such as Fujii's
earlier patch on this thread.
Any objections to commit to both head and 9.0?
Will then commit Fujii's patch.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Training and Services
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index bba247b..7c93f1e 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -156,6 +156,7 @@ static int KnownAssignedXidsGet(TransactionId *xarray, TransactionId xmax);
static int KnownAssignedXidsGetAndSetXmin(TransactionId *xarray,
TransactionId *xmin,
TransactionId xmax);
+static int KnownAssignedXidsGetOldestXmin(void);
static void KnownAssignedXidsDisplay(int trace_level);
/*
@@ -1112,6 +1113,18 @@ GetOldestXmin(bool allDbs, bool ignoreVacuum)
}
}
+ if (RecoveryInProgress())
+ {
+ /*
+ * Check to see whether KnownAssignedXids contains an xid value
+ * older than the main procarray.
+ */
+ TransactionId kaxmin = KnownAssignedXidsGetOldestXmin();
+ if (TransactionIdIsNormal(kaxmin) &&
+ TransactionIdPrecedes(kaxmin, result))
+ result = kaxmin;
+ }
+
LWLockRelease(ProcArrayLock);
/*
@@ -3015,6 +3028,33 @@ KnownAssignedXidsGetAndSetXmin(TransactionId *xarray, TransactionId *xmin,
return count;
}
+static int
+KnownAssignedXidsGetOldestXmin(void)
+{
+ /* use volatile pointer to prevent code rearrangement */
+ volatile ProcArrayStruct *pArray = procArray;
+ int head,
+ tail;
+ int i;
+
+ /*
+ * Fetch head just once, since it may change while we loop.
+ */
+ SpinLockAcquire(&pArray->known_assigned_xids_lck);
+ tail = pArray->tailKnownAssignedXids;
+ head = pArray->headKnownAssignedXids;
+ SpinLockRelease(&pArray->known_assigned_xids_lck);
+
+ for (i = tail; i < head; i++)
+ {
+ /* Skip any gaps in the array */
+ if (KnownAssignedXidsValid[i])
+ return KnownAssignedXids[i];
+ }
+
+ return InvalidTransactionId;
+}
+
/*
* Display KnownAssignedXids to provide debug trail
*
--
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