static void
check_toasted_attribute(HeapCheckContext *ctx, ToastedAttribute *ta)
{
- SnapshotData SnapshotToast;
ScanKeyData toastkey;
SysScanDesc toastscan;
bool found_toasttup;
* Check if any chunks for this toasted object exist in the toast table,
* accessible via the index.
*/
- init_toast_snapshot(&SnapshotToast);
toastscan = systable_beginscan_ordered(ctx->toast_rel,
ctx->valid_toast_index,
- &SnapshotToast, 1,
+ get_toast_snapshot(), 1,
&toastkey);
found_toasttup = false;
while ((toasttup =
HeapTuple toasttup;
int num_indexes;
int validIndex;
- SnapshotData SnapshotToast;
if (!VARATT_IS_EXTERNAL_ONDISK(attr))
return;
* 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);
+ get_toast_snapshot(), 1, &toastkey);
while ((toasttup = systable_getnext_ordered(toastscan, ForwardScanDirection)) != NULL)
{
/*
}
/* ----------
- * init_toast_snapshot
+ * get_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.
+ * Return the TOAST snapshot. Detoasting *must* happen in the same
+ * transaction that originally fetched the toast pointer.
*/
-void
-init_toast_snapshot(Snapshot toast_snapshot)
+Snapshot
+get_toast_snapshot(void)
{
- Snapshot snapshot = GetOldestSnapshot();
-
/*
- * GetOldestSnapshot returns NULL if the session has no active snapshots.
- * We can get that if, for example, a procedure fetches a toasted value
- * into a local variable, commits, and then tries to detoast the value.
- * Such coding is unsafe, because once we commit there is nothing to
- * prevent the toast data from being deleted. Detoasting *must* happen in
- * the same transaction that originally fetched the toast pointer. Hence,
- * rather than trying to band-aid over the problem, throw an error. (This
- * is not very much protection, because in many scenarios the procedure
- * would have already created a new transaction snapshot, preventing us
- * from detecting the problem. But it's better than nothing, and for sure
- * we shouldn't expend code on masking the problem more.)
+ * We cannot directly check that detoasting happens in the same
+ * transaction that originally fetched the toast pointer, but at least
+ * check that the session has some active snapshots. It might not if, for
+ * example, a procedure fetches a toasted value into a local variable,
+ * commits, and then tries to detoast the value. Such coding is unsafe,
+ * because once we commit there is nothing to prevent the toast data from
+ * being deleted. (This is not very much protection, because in many
+ * scenarios the procedure would have already created a new transaction
+ * snapshot, preventing us from detecting the problem. But it's better
+ * than nothing.)
*/
- if (snapshot == NULL)
+ if (!HaveRegisteredOrActiveSnapshot())
elog(ERROR, "cannot fetch toast data without an active snapshot");
- /*
- * Catalog snapshots can be returned by GetOldestSnapshot() even if not
- * registered or active. That easily hides bugs around not having a
- * snapshot set up - most of the time there is a valid catalog snapshot.
- * So additionally insist that the current snapshot is registered or
- * active.
- */
- Assert(HaveRegisteredOrActiveSnapshot());
-
- InitToastSnapshot(*toast_snapshot, snapshot->lsn, snapshot->whenTaken);
+ return &SnapshotToastData;
}
int endchunk;
int num_indexes;
int validIndex;
- SnapshotData SnapshotToast;
/* Look for the valid index of toast relation */
validIndex = toast_open_indexes(toastrel,
}
/* Prepare for scan */
- init_toast_snapshot(&SnapshotToast);
toastscan = systable_beginscan_ordered(toastrel, toastidxs[validIndex],
- &SnapshotToast, nscankeys, toastkey);
+ get_toast_snapshot(), nscankeys, toastkey);
/*
* Read the chunks by index
snapshot->active_count = 0;
snapshot->regd_count = 0;
snapshot->copied = false;
- snapshot->lsn = InvalidXLogRecPtr;
- snapshot->whenTaken = 0;
return true;
}
snapshot->active_count = 0;
snapshot->regd_count = 0;
snapshot->copied = false;
- snapshot->lsn = InvalidXLogRecPtr;
- snapshot->whenTaken = 0;
return snapshot;
}
SnapshotData CatalogSnapshotData = {SNAPSHOT_MVCC};
SnapshotData SnapshotSelfData = {SNAPSHOT_SELF};
SnapshotData SnapshotAnyData = {SNAPSHOT_ANY};
+SnapshotData SnapshotToastData = {SNAPSHOT_TOAST};
/* Pointers to valid snapshots */
static Snapshot CurrentSnapshot = NULL;
/* 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 MyProc->xmin.
bool suboverflowed;
bool takenDuringRecovery;
CommandId curcid;
- TimestampTz whenTaken;
- XLogRecPtr lsn;
} SerializedSnapshotData;
/*
return SecondarySnapshot;
}
-/*
- * GetOldestSnapshot
- *
- * Get the transaction's oldest known snapshot, as judged by the LSN.
- * Will return NULL if there are no active or registered snapshots.
- */
-Snapshot
-GetOldestSnapshot(void)
-{
- Snapshot OldestRegisteredSnapshot = NULL;
- XLogRecPtr RegisteredLSN = InvalidXLogRecPtr;
-
- if (!pairingheap_is_empty(&RegisteredSnapshots))
- {
- OldestRegisteredSnapshot = pairingheap_container(SnapshotData, ph_node,
- pairingheap_first(&RegisteredSnapshots));
- RegisteredLSN = OldestRegisteredSnapshot->lsn;
- }
-
- if (OldestActiveSnapshot != NULL)
- {
- XLogRecPtr 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
newactive->as_snap->active_count++;
ActiveSnapshot = newactive;
- if (OldestActiveSnapshot == NULL)
- OldestActiveSnapshot = ActiveSnapshot;
}
/*
pfree(ActiveSnapshot);
ActiveSnapshot = newstack;
- if (ActiveSnapshot == NULL)
- OldestActiveSnapshot = NULL;
SnapshotResetXmin();
}
* dropped. For efficiency, we only consider recomputing PGPROC->xmin when
* the active snapshot stack is empty; this allows us not to need to track
* which active snapshot is oldest.
- *
- * Note: it's tempting to use GetOldestSnapshot() here so that we can include
- * active snapshots in the calculation. However, that compares by LSN not
- * xmin so it's not entirely clear that it's the same thing. Also, we'd be
- * critically dependent on the assumption that the bottommost active snapshot
- * stack entry has the oldest xmin. (Current uses of GetOldestSnapshot() are
- * not actually critical, but this would be.)
*/
static void
SnapshotResetXmin(void)
pfree(ActiveSnapshot);
ActiveSnapshot = next;
- if (ActiveSnapshot == NULL)
- OldestActiveSnapshot = NULL;
}
SnapshotResetXmin();
* it'll go away with TopTransactionContext.
*/
ActiveSnapshot = NULL;
- OldestActiveSnapshot = NULL;
pairingheap_reset(&RegisteredSnapshots);
CurrentSnapshot = NULL;
serialized_snapshot.suboverflowed = snapshot->suboverflowed;
serialized_snapshot.takenDuringRecovery = snapshot->takenDuringRecovery;
serialized_snapshot.curcid = snapshot->curcid;
- serialized_snapshot.whenTaken = snapshot->whenTaken;
- serialized_snapshot.lsn = snapshot->lsn;
/*
* Ignore the SubXID array if it has overflowed, unless the snapshot was
snapshot->suboverflowed = serialized_snapshot.suboverflowed;
snapshot->takenDuringRecovery = serialized_snapshot.takenDuringRecovery;
snapshot->curcid = serialized_snapshot.curcid;
- snapshot->whenTaken = serialized_snapshot.whenTaken;
- snapshot->lsn = serialized_snapshot.lsn;
snapshot->snapXactCompletionCount = 0;
/* Copy XIDs, if present. */
#ifndef GENAM_H
#define GENAM_H
+#include "access/htup.h"
#include "access/sdir.h"
#include "access/skey.h"
#include "nodes/tidbitmap.h"
+#include "storage/buf.h"
#include "storage/lockdefs.h"
#include "utils/relcache.h"
#include "utils/snapshot.h"
int *num_indexes);
extern void toast_close_indexes(Relation *toastidxs, int num_indexes,
LOCKMODE lock);
-extern void init_toast_snapshot(Snapshot toast_snapshot);
+extern Snapshot get_toast_snapshot(void);
#endif /* TOAST_INTERNALS_H */
#ifndef PREDICATE_H
#define PREDICATE_H
+#include "storage/itemptr.h"
#include "storage/lock.h"
#include "utils/relcache.h"
#include "utils/snapshot.h"
/* Variables representing various special snapshot semantics */
extern PGDLLIMPORT SnapshotData SnapshotSelfData;
extern PGDLLIMPORT SnapshotData SnapshotAnyData;
+extern PGDLLIMPORT SnapshotData SnapshotToastData;
extern PGDLLIMPORT SnapshotData CatalogSnapshotData;
#define SnapshotSelf (&SnapshotSelfData)
#define SnapshotAny (&SnapshotAnyData)
+/* Use get_toast_snapshot() for the TOAST snapshot */
+
/*
* We don't provide a static SnapshotDirty variable because it would be
* non-reentrant. Instead, users of that snapshot type should declare a
((snapshotdata).snapshot_type = SNAPSHOT_NON_VACUUMABLE, \
(snapshotdata).vistest = (vistestp))
-/*
- * Similarly, some initialization is required for SnapshotToast. We need
- * to set lsn and whenTaken correctly to support snapshot_too_old.
- */
-#define InitToastSnapshot(snapshotdata, l, w) \
- ((snapshotdata).snapshot_type = SNAPSHOT_TOAST, \
- (snapshotdata).lsn = (l), \
- (snapshotdata).whenTaken = (w))
-
/* This macro encodes the knowledge of which snapshots are MVCC-safe */
#define IsMVCCSnapshot(snapshot) \
((snapshot)->snapshot_type == SNAPSHOT_MVCC || \
extern Snapshot GetTransactionSnapshot(void);
extern Snapshot GetLatestSnapshot(void);
extern void SnapshotSetCommandId(CommandId curcid);
-extern Snapshot GetOldestSnapshot(void);
extern Snapshot GetCatalogSnapshot(Oid relid);
extern Snapshot GetNonHistoricCatalogSnapshot(Oid relid);
#ifndef SNAPSHOT_H
#define SNAPSHOT_H
-#include "access/htup.h"
-#include "access/xlogdefs.h"
-#include "datatype/timestamp.h"
#include "lib/pairingheap.h"
-#include "storage/buf.h"
/*
uint32 regd_count; /* refcount on RegisteredSnapshots */
pairingheap_node ph_node; /* link in the RegisteredSnapshots heap */
- TimestampTz whenTaken; /* timestamp when snapshot was taken */
- XLogRecPtr lsn; /* position in the WAL stream when taken */
-
/*
* The transaction completion count at the time GetSnapshotData() built
* this snapshot. Allows to avoid re-computing static snapshots when no
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