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/*-------------------------------------------------------------------------
*
* snapmgr.h
* POSTGRES snapshot manager
*
* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/utils/snapmgr.h
*
*-------------------------------------------------------------------------
*/
#ifndef SNAPMGR_H
#define SNAPMGR_H
#include "access/transam.h"
#include "utils/relcache.h"
#include "utils/resowner.h"
#include "utils/snapshot.h"
/*
* The structure used to map times to TransactionId values for the "snapshot
* too old" feature must have a few entries at the tail to hold old values;
* otherwise the lookup will often fail and the expected early pruning or
* vacuum will not usually occur. It is best if this padding is for a number
* of minutes greater than a thread would normally be stalled, but it's OK if
* early vacuum opportunities are occasionally missed, so there's no need to
* use an extreme value or get too fancy. 10 minutes seems plenty.
*/
#define OLD_SNAPSHOT_PADDING_ENTRIES 10
#define OLD_SNAPSHOT_TIME_MAP_ENTRIES (old_snapshot_threshold + OLD_SNAPSHOT_PADDING_ENTRIES)
/*
* Common definition of relation properties that allow early pruning/vacuuming
* when old_snapshot_threshold >= 0.
*/
#define RelationAllowsEarlyPruning(rel) \
( \
RelationIsPermanent(rel) && !IsCatalogRelation(rel) \
&& !RelationIsAccessibleInLogicalDecoding(rel) \
)
#define EarlyPruningEnabled(rel) (old_snapshot_threshold >= 0 && RelationAllowsEarlyPruning(rel))
/* GUC variables */
extern __thread PGDLLIMPORT int old_snapshot_threshold;
extern Size SnapMgrShmemSize(void);
extern void SnapMgrInit(void);
extern TimestampTz GetSnapshotCurrentTimestamp(void);
extern TimestampTz GetOldSnapshotThresholdTimestamp(void);
extern void SnapshotTooOldMagicForTest(void);
extern __thread PGDLLIMPORT bool FirstSnapshotSet;
extern __thread PGDLLIMPORT TransactionId TransactionXmin;
extern __thread PGDLLIMPORT TransactionId RecentXmin;
/* Variables representing various special snapshot semantics */
extern __thread PGDLLIMPORT SnapshotData SnapshotSelfData;
extern __thread PGDLLIMPORT SnapshotData SnapshotAnyData;
extern __thread PGDLLIMPORT SnapshotData CatalogSnapshotData;
#define SnapshotSelf (&SnapshotSelfData)
#define SnapshotAny (&SnapshotAnyData)
/*
* We don't provide a static SnapshotDirty variable because it would be
* non-reentrant. Instead, users of that snapshot type should declare a
* local variable of type SnapshotData, and initialize it with this macro.
*/
#define InitDirtySnapshot(snapshotdata) \
((snapshotdata).snapshot_type = SNAPSHOT_DIRTY)
/*
* Similarly, some initialization is required for a NonVacuumable snapshot.
* The caller must supply the visibility cutoff state to use (c.f.
* GlobalVisTestFor()).
*/
#define InitNonVacuumableSnapshot(snapshotdata, vistestp) \
((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 || \
(snapshot)->snapshot_type == SNAPSHOT_HISTORIC_MVCC)
#ifndef FRONTEND
static inline bool
OldSnapshotThresholdActive(void)
{
return old_snapshot_threshold >= 0;
}
#endif
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);
extern void InvalidateCatalogSnapshot(void);
extern void InvalidateCatalogSnapshotConditionally(void);
extern void PushActiveSnapshot(Snapshot snapshot);
extern void PushActiveSnapshotWithLevel(Snapshot snapshot, int snap_level);
extern void PushCopiedSnapshot(Snapshot snapshot);
extern void UpdateActiveSnapshotCommandId(void);
extern void PopActiveSnapshot(void);
extern Snapshot GetActiveSnapshot(void);
extern bool ActiveSnapshotSet(void);
extern Snapshot RegisterSnapshot(Snapshot snapshot);
extern void UnregisterSnapshot(Snapshot snapshot);
extern Snapshot RegisterSnapshotOnOwner(Snapshot snapshot, ResourceOwner owner);
extern void UnregisterSnapshotFromOwner(Snapshot snapshot, ResourceOwner owner);
extern void AtSubCommit_Snapshot(int level);
extern void AtSubAbort_Snapshot(int level);
extern void AtEOXact_Snapshot(bool isCommit, bool resetXmin);
extern void ImportSnapshot(const char *idstr);
extern bool XactHasExportedSnapshots(void);
extern void DeleteAllExportedSnapshotFiles(void);
extern void WaitForOlderSnapshots(TransactionId limitXmin, bool progress);
extern bool ThereAreNoPriorRegisteredSnapshots(void);
extern bool HaveRegisteredOrActiveSnapshot(void);
extern bool TransactionIdLimitedForOldSnapshots(TransactionId recentXmin,
Relation relation,
TransactionId *limit_xid,
TimestampTz *limit_ts);
extern void SetOldSnapshotThresholdTimestamp(TimestampTz ts, TransactionId xlimit);
extern void MaintainOldSnapshotTimeMapping(TimestampTz whenTaken,
TransactionId xmin);
extern char *ExportSnapshot(Snapshot snapshot);
/*
* These live in procarray.c because they're intimately linked to the
* procarray contents, but thematically they better fit into snapmgr.h.
*/
typedef struct GlobalVisState GlobalVisState;
extern GlobalVisState *GlobalVisTestFor(Relation rel);
extern bool GlobalVisTestIsRemovableXid(GlobalVisState *state, TransactionId xid);
extern bool GlobalVisTestIsRemovableFullXid(GlobalVisState *state, FullTransactionId fxid);
extern FullTransactionId GlobalVisTestNonRemovableFullHorizon(GlobalVisState *state);
extern TransactionId GlobalVisTestNonRemovableHorizon(GlobalVisState *state);
extern bool GlobalVisCheckRemovableXid(Relation rel, TransactionId xid);
extern bool GlobalVisCheckRemovableFullXid(Relation rel, FullTransactionId fxid);
/*
* Utility functions for implementing visibility routines in table AMs.
*/
extern bool XidInMVCCSnapshot(TransactionId xid, Snapshot snapshot);
/* Support for catalog timetravel for logical decoding */
struct HTAB;
extern struct HTAB *HistoricSnapshotGetTupleCids(void);
extern void SetupHistoricSnapshot(Snapshot historic_snapshot, struct HTAB *tuplecids);
extern void TeardownHistoricSnapshot(bool is_error);
extern bool HistoricSnapshotActive(void);
extern Size EstimateSnapshotSpace(Snapshot snapshot);
extern void SerializeSnapshot(Snapshot snapshot, char *start_address);
extern Snapshot RestoreSnapshot(char *start_address);
extern void RestoreTransactionSnapshot(Snapshot snapshot, void *source_pgproc);
#endif /* SNAPMGR_H */
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