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132 lines
4.4 KiB
C
132 lines
4.4 KiB
C
/*-------------------------------------------------------------------------
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*
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* snapshot.h
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* POSTGRES snapshot definition
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*
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* Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/utils/snapshot.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef SNAPSHOT_H
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#define SNAPSHOT_H
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#include "access/htup.h"
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#include "access/xlogdefs.h"
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#include "datatype/timestamp.h"
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#include "lib/pairingheap.h"
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#include "storage/buf.h"
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typedef struct SnapshotData *Snapshot;
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#define InvalidSnapshot ((Snapshot) NULL)
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/*
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* We use SnapshotData structures to represent both "regular" (MVCC)
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* snapshots and "special" snapshots that have non-MVCC semantics.
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* The specific semantics of a snapshot are encoded by the "satisfies"
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* function.
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*/
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typedef bool (*SnapshotSatisfiesFunc) (HeapTuple htup,
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Snapshot snapshot, Buffer buffer);
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/*
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* Struct representing all kind of possible snapshots.
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*
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* There are several different kinds of snapshots:
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* * Normal MVCC snapshots
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* * MVCC snapshots taken during recovery (in Hot-Standby mode)
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* * Historic MVCC snapshots used during logical decoding
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* * snapshots passed to HeapTupleSatisfiesDirty()
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* * snapshots passed to HeapTupleSatisfiesNonVacuumable()
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* * snapshots used for SatisfiesAny, Toast, Self where no members are
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* accessed.
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*
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* TODO: It's probably a good idea to split this struct using a NodeTag
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* similar to how parser and executor nodes are handled, with one type for
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* each different kind of snapshot to avoid overloading the meaning of
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* individual fields.
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*/
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typedef struct SnapshotData
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{
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SnapshotSatisfiesFunc satisfies; /* tuple test function */
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/*
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* The remaining fields are used only for MVCC snapshots, and are normally
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* just zeroes in special snapshots. (But xmin and xmax are used
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* specially by HeapTupleSatisfiesDirty, and xmin is used specially by
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* HeapTupleSatisfiesNonVacuumable.)
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*
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* An MVCC snapshot can never see the effects of XIDs >= xmax. It can see
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* the effects of all older XIDs except those listed in the snapshot. xmin
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* is stored as an optimization to avoid needing to search the XID arrays
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* for most tuples.
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*/
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TransactionId xmin; /* all XID < xmin are visible to me */
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TransactionId xmax; /* all XID >= xmax are invisible to me */
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/*
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* For normal MVCC snapshot this contains the all xact IDs that are in
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* progress, unless the snapshot was taken during recovery in which case
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* it's empty. For historic MVCC snapshots, the meaning is inverted, i.e.
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* it contains *committed* transactions between xmin and xmax.
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*
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* note: all ids in xip[] satisfy xmin <= xip[i] < xmax
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*/
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TransactionId *xip;
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uint32 xcnt; /* # of xact ids in xip[] */
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/*
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* For non-historic MVCC snapshots, this contains subxact IDs that are in
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* progress (and other transactions that are in progress if taken during
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* recovery). For historic snapshot it contains *all* xids assigned to the
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* replayed transaction, including the toplevel xid.
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*
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* note: all ids in subxip[] are >= xmin, but we don't bother filtering
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* out any that are >= xmax
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*/
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TransactionId *subxip;
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int32 subxcnt; /* # of xact ids in subxip[] */
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bool suboverflowed; /* has the subxip array overflowed? */
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bool takenDuringRecovery; /* recovery-shaped snapshot? */
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bool copied; /* false if it's a static snapshot */
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CommandId curcid; /* in my xact, CID < curcid are visible */
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/*
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* An extra return value for HeapTupleSatisfiesDirty, not used in MVCC
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* snapshots.
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*/
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uint32 speculativeToken;
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/*
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* Book-keeping information, used by the snapshot manager
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*/
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uint32 active_count; /* refcount on ActiveSnapshot stack */
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uint32 regd_count; /* refcount on RegisteredSnapshots */
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pairingheap_node ph_node; /* link in the RegisteredSnapshots heap */
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TimestampTz whenTaken; /* timestamp when snapshot was taken */
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XLogRecPtr lsn; /* position in the WAL stream when taken */
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} SnapshotData;
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/*
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* Result codes for HeapTupleSatisfiesUpdate. This should really be in
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* tqual.h, but we want to avoid including that file elsewhere.
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*/
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typedef enum
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{
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HeapTupleMayBeUpdated,
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HeapTupleInvisible,
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HeapTupleSelfUpdated,
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HeapTupleUpdated,
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HeapTupleBeingUpdated,
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HeapTupleWouldBlock /* can be returned by heap_tuple_lock */
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} HTSU_Result;
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#endif /* SNAPSHOT_H */
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