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-rw-r--r--src/backend/access/heap/tuptoaster.c37
-rw-r--r--src/backend/utils/time/snapmgr.c38
-rw-r--r--src/backend/utils/time/tqual.c1
3 files changed, 71 insertions, 5 deletions
diff --git a/src/backend/access/heap/tuptoaster.c b/src/backend/access/heap/tuptoaster.c
index 4cffd21d180..55b6b41f8c7 100644
--- a/src/backend/access/heap/tuptoaster.c
+++ b/src/backend/access/heap/tuptoaster.c
@@ -40,6 +40,7 @@
#include "utils/expandeddatum.h"
#include "utils/fmgroids.h"
#include "utils/rel.h"
+#include "utils/snapmgr.h"
#include "utils/typcache.h"
#include "utils/tqual.h"
@@ -81,6 +82,7 @@ static int toast_open_indexes(Relation toastrel,
int *num_indexes);
static void toast_close_indexes(Relation *toastidxs, int num_indexes,
LOCKMODE lock);
+static void init_toast_snapshot(Snapshot toast_snapshot);
/* ----------
@@ -1665,6 +1667,7 @@ toast_delete_datum(Relation rel, Datum value)
HeapTuple toasttup;
int num_indexes;
int validIndex;
+ SnapshotData SnapshotToast;
if (!VARATT_IS_EXTERNAL_ONDISK(attr))
return;
@@ -1696,8 +1699,9 @@ toast_delete_datum(Relation rel, Datum value)
* sequence or not, but since we've already locked the index we might as
* well use systable_beginscan_ordered.)
*/
+ init_toast_snapshot(&SnapshotToast);
toastscan = systable_beginscan_ordered(toastrel, toastidxs[validIndex],
- SnapshotToast, 1, &toastkey);
+ &SnapshotToast, 1, &toastkey);
while ((toasttup = systable_getnext_ordered(toastscan, ForwardScanDirection)) != NULL)
{
/*
@@ -1730,6 +1734,7 @@ toastrel_valueid_exists(Relation toastrel, Oid valueid)
int num_indexes;
int validIndex;
Relation *toastidxs;
+ SnapshotData SnapshotToast;
/* Fetch a valid index relation */
validIndex = toast_open_indexes(toastrel,
@@ -1748,9 +1753,10 @@ toastrel_valueid_exists(Relation toastrel, Oid valueid)
/*
* Is there any such chunk?
*/
+ init_toast_snapshot(&SnapshotToast);
toastscan = systable_beginscan(toastrel,
RelationGetRelid(toastidxs[validIndex]),
- true, SnapshotToast, 1, &toastkey);
+ true, &SnapshotToast, 1, &toastkey);
if (systable_getnext(toastscan) != NULL)
result = true;
@@ -1813,6 +1819,7 @@ toast_fetch_datum(struct varlena * attr)
int32 chunksize;
int num_indexes;
int validIndex;
+ SnapshotData SnapshotToast;
if (!VARATT_IS_EXTERNAL_ONDISK(attr))
elog(ERROR, "toast_fetch_datum shouldn't be called for non-ondisk datums");
@@ -1859,8 +1866,9 @@ toast_fetch_datum(struct varlena * attr)
*/
nextidx = 0;
+ init_toast_snapshot(&SnapshotToast);
toastscan = systable_beginscan_ordered(toastrel, toastidxs[validIndex],
- SnapshotToast, 1, &toastkey);
+ &SnapshotToast, 1, &toastkey);
while ((ttup = systable_getnext_ordered(toastscan, ForwardScanDirection)) != NULL)
{
/*
@@ -1990,6 +1998,7 @@ toast_fetch_datum_slice(struct varlena * attr, int32 sliceoffset, int32 length)
int32 chcpyend;
int num_indexes;
int validIndex;
+ SnapshotData SnapshotToast;
if (!VARATT_IS_EXTERNAL_ONDISK(attr))
elog(ERROR, "toast_fetch_datum_slice shouldn't be called for non-ondisk datums");
@@ -2082,9 +2091,10 @@ toast_fetch_datum_slice(struct varlena * attr, int32 sliceoffset, int32 length)
*
* The index is on (valueid, chunkidx) so they will come in order
*/
+ init_toast_snapshot(&SnapshotToast);
nextidx = startchunk;
toastscan = systable_beginscan_ordered(toastrel, toastidxs[validIndex],
- SnapshotToast, nscankeys, toastkey);
+ &SnapshotToast, nscankeys, toastkey);
while ((ttup = systable_getnext_ordered(toastscan, ForwardScanDirection)) != NULL)
{
/*
@@ -2289,3 +2299,22 @@ toast_close_indexes(Relation *toastidxs, int num_indexes, LOCKMODE lock)
index_close(toastidxs[i], lock);
pfree(toastidxs);
}
+
+/* ----------
+ * init_toast_snapshot
+ *
+ * Initialize an appropriate TOAST snapshot. We must use an MVCC snapshot
+ * to initialize the TOAST snapshot; since we don't know which one to use,
+ * just use the oldest one. This is safe: at worst, we will get a "snapshot
+ * too old" error that might have been avoided otherwise.
+ */
+static void
+init_toast_snapshot(Snapshot toast_snapshot)
+{
+ Snapshot snapshot = GetOldestSnapshot();
+
+ if (snapshot == NULL)
+ elog(ERROR, "no known snapshots");
+
+ InitToastSnapshot(toast_snapshot, snapshot->lsn, snapshot->whenTaken);
+}
diff --git a/src/backend/utils/time/snapmgr.c b/src/backend/utils/time/snapmgr.c
index e1caf01c603..4bddaed33ba 100644
--- a/src/backend/utils/time/snapmgr.c
+++ b/src/backend/utils/time/snapmgr.c
@@ -188,6 +188,9 @@ typedef struct ActiveSnapshotElt
/* Top of the stack of active snapshots */
static ActiveSnapshotElt *ActiveSnapshot = NULL;
+/* Bottom of the stack of active snapshots */
+static ActiveSnapshotElt *OldestActiveSnapshot = NULL;
+
/*
* Currently registered Snapshots. Ordered in a heap by xmin, so that we can
* quickly find the one with lowest xmin, to advance our MyPgXat->xmin.
@@ -394,6 +397,34 @@ GetLatestSnapshot(void)
}
/*
+ * GetOldestSnapshot
+ *
+ * Get the oldest known snapshot, as judged by the LSN.
+ */
+Snapshot
+GetOldestSnapshot(void)
+{
+ Snapshot OldestRegisteredSnapshot = NULL;
+ XLogRecPtr RegisteredLSN = InvalidXLogRecPtr;
+ XLogRecPtr ActiveLSN = InvalidXLogRecPtr;
+
+ if (!pairingheap_is_empty(&RegisteredSnapshots))
+ {
+ OldestRegisteredSnapshot = pairingheap_container(SnapshotData, ph_node,
+ pairingheap_first(&RegisteredSnapshots));
+ RegisteredLSN = OldestRegisteredSnapshot->lsn;
+ }
+
+ if (OldestActiveSnapshot != NULL)
+ ActiveLSN = OldestActiveSnapshot->as_snap->lsn;
+
+ if (XLogRecPtrIsInvalid(RegisteredLSN) || RegisteredLSN > ActiveLSN)
+ return OldestActiveSnapshot->as_snap;
+
+ return OldestRegisteredSnapshot;
+}
+
+/*
* GetCatalogSnapshot
* Get a snapshot that is sufficiently up-to-date for scan of the
* system catalog with the specified OID.
@@ -674,6 +705,8 @@ PushActiveSnapshot(Snapshot snap)
newactive->as_snap->active_count++;
ActiveSnapshot = newactive;
+ if (OldestActiveSnapshot == NULL)
+ OldestActiveSnapshot = ActiveSnapshot;
}
/*
@@ -744,6 +777,8 @@ PopActiveSnapshot(void)
pfree(ActiveSnapshot);
ActiveSnapshot = newstack;
+ if (ActiveSnapshot == NULL)
+ OldestActiveSnapshot = NULL;
SnapshotResetXmin();
}
@@ -953,6 +988,8 @@ AtSubAbort_Snapshot(int level)
pfree(ActiveSnapshot);
ActiveSnapshot = next;
+ if (ActiveSnapshot == NULL)
+ OldestActiveSnapshot = NULL;
}
SnapshotResetXmin();
@@ -1037,6 +1074,7 @@ AtEOXact_Snapshot(bool isCommit)
* it'll go away with TopTransactionContext.
*/
ActiveSnapshot = NULL;
+ OldestActiveSnapshot = NULL;
pairingheap_reset(&RegisteredSnapshots);
CurrentSnapshot = NULL;
diff --git a/src/backend/utils/time/tqual.c b/src/backend/utils/time/tqual.c
index 2960455d6e3..d99c847000e 100644
--- a/src/backend/utils/time/tqual.c
+++ b/src/backend/utils/time/tqual.c
@@ -78,7 +78,6 @@
/* Static variables representing various special snapshot semantics */
SnapshotData SnapshotSelfData = {HeapTupleSatisfiesSelf};
SnapshotData SnapshotAnyData = {HeapTupleSatisfiesAny};
-SnapshotData SnapshotToastData = {HeapTupleSatisfiesToast};
/* local functions */
static bool XidInMVCCSnapshot(TransactionId xid, Snapshot snapshot);
generated by cgit v1.2.3 (git 2.25.1) at 2025-07-15 15:37:38 +0000