1 /*-------------------------------------------------------------------------
2 *
3 * snapmgr.h
4 * POSTGRES snapshot manager
5 *
6 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
7 * Portions Copyright (c) 1994, Regents of the University of California
8 *
9 * src/include/utils/snapmgr.h
10 *
11 *-------------------------------------------------------------------------
12 */
13 #ifndef SNAPMGR_H
14 #define SNAPMGR_H
15
16 #include "access/transam.h"
17 #include "utils/relcache.h"
18 #include "utils/resowner.h"
19 #include "utils/snapshot.h"
20
21
22 /*
23 * The structure used to map times to TransactionId values for the "snapshot
24 * too old" feature must have a few entries at the tail to hold old values;
25 * otherwise the lookup will often fail and the expected early pruning or
26 * vacuum will not usually occur. It is best if this padding is for a number
27 * of minutes greater than a thread would normally be stalled, but it's OK if
28 * early vacuum opportunities are occasionally missed, so there's no need to
29 * use an extreme value or get too fancy. 10 minutes seems plenty.
30 */
31 #define OLD_SNAPSHOT_PADDING_ENTRIES 10
32 #define OLD_SNAPSHOT_TIME_MAP_ENTRIES (old_snapshot_threshold + OLD_SNAPSHOT_PADDING_ENTRIES)
33
34 /*
35 * Common definition of relation properties that allow early pruning/vacuuming
36 * when old_snapshot_threshold >= 0.
37 */
38 #define RelationAllowsEarlyPruning(rel) \
39 ( \
40 RelationIsPermanent(rel) && !IsCatalogRelation(rel) \
41 && !RelationIsAccessibleInLogicalDecoding(rel) \
42 )
43
44 #define EarlyPruningEnabled(rel) (old_snapshot_threshold >= 0 && RelationAllowsEarlyPruning(rel))
45
46 /* GUC variables */
47 extern PGDLLIMPORT int old_snapshot_threshold;
48
49
50 extern Size SnapMgrShmemSize(void);
51 extern void SnapMgrInit(void);
52 extern TimestampTz GetSnapshotCurrentTimestamp(void);
53 extern TimestampTz GetOldSnapshotThresholdTimestamp(void);
54 extern void SnapshotTooOldMagicForTest(void);
55
56 extern bool FirstSnapshotSet;
57
58 extern PGDLLIMPORT TransactionId TransactionXmin;
59 extern PGDLLIMPORT TransactionId RecentXmin;
60
61 /* Variables representing various special snapshot semantics */
62 extern PGDLLIMPORT SnapshotData SnapshotSelfData;
63 extern PGDLLIMPORT SnapshotData SnapshotAnyData;
64 extern PGDLLIMPORT SnapshotData CatalogSnapshotData;
65
66 #define SnapshotSelf (&SnapshotSelfData)
67 #define SnapshotAny (&SnapshotAnyData)
68
69 /*
70 * We don't provide a static SnapshotDirty variable because it would be
71 * non-reentrant. Instead, users of that snapshot type should declare a
72 * local variable of type SnapshotData, and initialize it with this macro.
73 */
74 #define InitDirtySnapshot(snapshotdata) \
75 ((snapshotdata).snapshot_type = SNAPSHOT_DIRTY)
76
77 /*
78 * Similarly, some initialization is required for a NonVacuumable snapshot.
79 * The caller must supply the visibility cutoff state to use (c.f.
80 * GlobalVisTestFor()).
81 */
82 #define InitNonVacuumableSnapshot(snapshotdata, vistestp) \
83 ((snapshotdata).snapshot_type = SNAPSHOT_NON_VACUUMABLE, \
84 (snapshotdata).vistest = (vistestp))
85
86 /*
87 * Similarly, some initialization is required for SnapshotToast. We need
88 * to set lsn and whenTaken correctly to support snapshot_too_old.
89 */
90 #define InitToastSnapshot(snapshotdata, l, w) \
91 ((snapshotdata).snapshot_type = SNAPSHOT_TOAST, \
92 (snapshotdata).lsn = (l), \
93 (snapshotdata).whenTaken = (w))
94
95 /* This macro encodes the knowledge of which snapshots are MVCC-safe */
96 #define IsMVCCSnapshot(snapshot) \
97 ((snapshot)->snapshot_type == SNAPSHOT_MVCC || \
98 (snapshot)->snapshot_type == SNAPSHOT_HISTORIC_MVCC)
99
100 static inline bool
OldSnapshotThresholdActive(void)101 OldSnapshotThresholdActive(void)
102 {
103 return old_snapshot_threshold >= 0;
104 }
105
106 extern Snapshot GetTransactionSnapshot(void);
107 extern Snapshot GetLatestSnapshot(void);
108 extern void SnapshotSetCommandId(CommandId curcid);
109 extern Snapshot GetOldestSnapshot(void);
110
111 extern Snapshot GetCatalogSnapshot(Oid relid);
112 extern Snapshot GetNonHistoricCatalogSnapshot(Oid relid);
113 extern void InvalidateCatalogSnapshot(void);
114 extern void InvalidateCatalogSnapshotConditionally(void);
115
116 extern void PushActiveSnapshot(Snapshot snapshot);
117 extern void PushActiveSnapshotWithLevel(Snapshot snapshot, int snap_level);
118 extern void PushCopiedSnapshot(Snapshot snapshot);
119 extern void UpdateActiveSnapshotCommandId(void);
120 extern void PopActiveSnapshot(void);
121 extern Snapshot GetActiveSnapshot(void);
122 extern bool ActiveSnapshotSet(void);
123
124 extern Snapshot RegisterSnapshot(Snapshot snapshot);
125 extern void UnregisterSnapshot(Snapshot snapshot);
126 extern Snapshot RegisterSnapshotOnOwner(Snapshot snapshot, ResourceOwner owner);
127 extern void UnregisterSnapshotFromOwner(Snapshot snapshot, ResourceOwner owner);
128
129 extern void AtSubCommit_Snapshot(int level);
130 extern void AtSubAbort_Snapshot(int level);
131 extern void AtEOXact_Snapshot(bool isCommit, bool resetXmin);
132
133 extern void ImportSnapshot(const char *idstr);
134 extern bool XactHasExportedSnapshots(void);
135 extern void DeleteAllExportedSnapshotFiles(void);
136 extern void WaitForOlderSnapshots(TransactionId limitXmin, bool progress);
137 extern bool ThereAreNoPriorRegisteredSnapshots(void);
138 extern bool TransactionIdLimitedForOldSnapshots(TransactionId recentXmin,
139 Relation relation,
140 TransactionId *limit_xid,
141 TimestampTz *limit_ts);
142 extern void SetOldSnapshotThresholdTimestamp(TimestampTz ts, TransactionId xlimit);
143 extern void MaintainOldSnapshotTimeMapping(TimestampTz whenTaken,
144 TransactionId xmin);
145
146 extern char *ExportSnapshot(Snapshot snapshot);
147
148 /*
149 * These live in procarray.c because they're intimately linked to the
150 * procarray contents, but thematically they better fit into snapmgr.h.
151 */
152 typedef struct GlobalVisState GlobalVisState;
153 extern GlobalVisState *GlobalVisTestFor(Relation rel);
154 extern bool GlobalVisTestIsRemovableXid(GlobalVisState *state, TransactionId xid);
155 extern bool GlobalVisTestIsRemovableFullXid(GlobalVisState *state, FullTransactionId fxid);
156 extern FullTransactionId GlobalVisTestNonRemovableFullHorizon(GlobalVisState *state);
157 extern TransactionId GlobalVisTestNonRemovableHorizon(GlobalVisState *state);
158 extern bool GlobalVisCheckRemovableXid(Relation rel, TransactionId xid);
159 extern bool GlobalVisCheckRemovableFullXid(Relation rel, FullTransactionId fxid);
160
161 /*
162 * Utility functions for implementing visibility routines in table AMs.
163 */
164 extern bool XidInMVCCSnapshot(TransactionId xid, Snapshot snapshot);
165
166 /* Support for catalog timetravel for logical decoding */
167 struct HTAB;
168 extern struct HTAB *HistoricSnapshotGetTupleCids(void);
169 extern void SetupHistoricSnapshot(Snapshot snapshot_now, struct HTAB *tuplecids);
170 extern void TeardownHistoricSnapshot(bool is_error);
171 extern bool HistoricSnapshotActive(void);
172
173 extern Size EstimateSnapshotSpace(Snapshot snapshot);
174 extern void SerializeSnapshot(Snapshot snapshot, char *start_address);
175 extern Snapshot RestoreSnapshot(char *start_address);
176 extern void RestoreTransactionSnapshot(Snapshot snapshot, void *source_pgproc);
177
178 #endif /* SNAPMGR_H */
179