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/*-------------------------------------------------------------------------
*
* snapmgr.h
* POSTGRES snapshot manager
*
* Portions Copyright (c) 1996-2020, 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) \
( \
(rel)->rd_rel->relpersistence == RELPERSISTENCE_PERMANENT \
&& !IsCatalogRelation(rel) \
&& !RelationIsAccessibleInLogicalDecoding(rel) \
)
#define EarlyPruningEnabled(rel) (old_snapshot_threshold >= 0 && RelationAllowsEarlyPruning(rel))
/* GUC variables */
extern PGDLLIMPORT int old_snapshot_threshold;
extern Size SnapMgrShmemSize(void);
extern void SnapMgrInit(void);
extern TimestampTz GetSnapshotCurrentTimestamp(void);
extern TimestampTz GetOldSnapshotThresholdTimestamp(void);
extern bool FirstSnapshotSet;
extern PGDLLIMPORT TransactionId TransactionXmin;
extern PGDLLIMPORT TransactionId RecentXmin;
extern PGDLLIMPORT TransactionId RecentGlobalXmin;
extern PGDLLIMPORT TransactionId RecentGlobalDataXmin;
/* Variables representing various special snapshot semantics */
extern PGDLLIMPORT SnapshotData SnapshotSelfData;
extern PGDLLIMPORT SnapshotData SnapshotAnyData;
extern 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 xmin horizon to use (e.g., RecentGlobalXmin).
*/
#define InitNonVacuumableSnapshot(snapshotdata, xmin_horizon) \
((snapshotdata).snapshot_type = SNAPSHOT_NON_VACUUMABLE, \
(snapshotdata).xmin = (xmin_horizon))
/*
* 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)
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 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 FullTransactionId GetFullRecentGlobalXmin(void);
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 bool ThereAreNoPriorRegisteredSnapshots(void);
extern TransactionId TransactionIdLimitedForOldSnapshots(TransactionId recentXmin,
Relation relation);
extern void MaintainOldSnapshotTimeMapping(TimestampTz whenTaken,
TransactionId xmin);
extern char *ExportSnapshot(Snapshot snapshot);
/*
* 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 snapshot_now, 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 *master_pgproc);
#endif /* SNAPMGR_H */
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