1 /*-------------------------------------------------------------------------
4 * POSTGRES snapshot definition
6 * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
7 * Portions Copyright (c) 1994, Regents of the University of California
9 * src/include/utils/snapshot.h
11 *-------------------------------------------------------------------------
16 #include "access/htup.h"
17 #include "storage/buf.h"
20 typedef struct SnapshotData *Snapshot;
22 #define InvalidSnapshot ((Snapshot) NULL)
25 * We use SnapshotData structures to represent both "regular" (MVCC)
26 * snapshots and "special" snapshots that have non-MVCC semantics.
27 * The specific semantics of a snapshot are encoded by the "satisfies"
30 typedef bool (*SnapshotSatisfiesFunc) (HeapTupleHeader tuple,
31 Snapshot snapshot, Buffer buffer);
33 typedef struct SnapshotData
35 SnapshotSatisfiesFunc satisfies; /* tuple test function */
38 * The remaining fields are used only for MVCC snapshots, and are normally
39 * just zeroes in special snapshots. (But xmin and xmax are used
40 * specially by HeapTupleSatisfiesDirty.)
42 * An MVCC snapshot can never see the effects of XIDs >= xmax. It can see
43 * the effects of all older XIDs except those listed in the snapshot. xmin
44 * is stored as an optimization to avoid needing to search the XID arrays
47 TransactionId xmin; /* all XID < xmin are visible to me */
48 TransactionId xmax; /* all XID >= xmax are invisible to me */
49 uint32 xcnt; /* # of xact ids in xip[] */
50 TransactionId *xip; /* array of xact IDs in progress */
51 /* note: all ids in xip[] satisfy xmin <= xip[i] < xmax */
52 int32 subxcnt; /* # of xact ids in subxip[] */
53 TransactionId *subxip; /* array of subxact IDs in progress */
54 bool suboverflowed; /* has the subxip array overflowed? */
55 bool takenDuringRecovery; /* recovery-shaped snapshot? */
58 * note: all ids in subxip[] are >= xmin, but we don't bother filtering
59 * out any that are >= xmax
61 CommandId curcid; /* in my xact, CID < curcid are visible */
62 uint32 active_count; /* refcount on ActiveSnapshot stack */
63 uint32 regd_count; /* refcount on RegisteredSnapshotList */
64 bool copied; /* false if it's a static snapshot */
68 * Result codes for HeapTupleSatisfiesUpdate. This should really be in
69 * tqual.h, but we want to avoid including that file elsewhere.
73 HeapTupleMayBeUpdated,
80 #endif /* SNAPSHOT_H */