snapmgr.h

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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) \
( \
     RelationNeedsWAL(rel) \
  && !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 */