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1fc3d18faa
This squeezes out a bunch of alignment padding, reducing the size from 72 to 56 bytes on my machine. At least in my testing, this didn't produce any measurable performance improvement, but the space savings seem like enough justification. Andres Freund
81 lines
2.6 KiB
C
81 lines
2.6 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) 1996-2012, 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 "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) (HeapTupleHeader tuple,
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Snapshot snapshot, Buffer buffer);
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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.)
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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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TransactionId *xip; /* array of xact IDs in progress */
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uint32 xcnt; /* # of xact ids in xip[] */
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/* note: all ids in xip[] satisfy xmin <= xip[i] < xmax */
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int32 subxcnt; /* # of xact ids in subxip[] */
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TransactionId *subxip; /* array of subxact IDs in progress */
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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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/*
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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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CommandId curcid; /* in my xact, CID < curcid are visible */
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uint32 active_count; /* refcount on ActiveSnapshot stack */
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uint32 regd_count; /* refcount on RegisteredSnapshotList */
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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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} HTSU_Result;
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#endif /* SNAPSHOT_H */
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