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pg_include/utils/snapshot.h

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+/*-------------------------------------------------------------------------
+ *
+ * snapshot.h
+ *	  POSTGRES snapshot definition
+ *
+ * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/utils/snapshot.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef SNAPSHOT_H
+#define SNAPSHOT_H
+
+#include "access/htup.h"
+#include "storage/buf.h"
+
+
+typedef struct SnapshotData *Snapshot;
+
+#define InvalidSnapshot		((Snapshot) NULL)
+
+/*
+ * We use SnapshotData structures to represent both "regular" (MVCC)
+ * snapshots and "special" snapshots that have non-MVCC semantics.
+ * The specific semantics of a snapshot are encoded by the "satisfies"
+ * function.
+ */
+typedef bool (*SnapshotSatisfiesFunc) (HeapTupleHeader tuple,
+										   Snapshot snapshot, Buffer buffer);
+
+typedef struct SnapshotData
+{
+	SnapshotSatisfiesFunc satisfies;	/* tuple test function */
+
+	/*
+	 * The remaining fields are used only for MVCC snapshots, and are normally
+	 * just zeroes in special snapshots.  (But xmin and xmax are used
+	 * specially by HeapTupleSatisfiesDirty.)
+	 *
+	 * An MVCC snapshot can never see the effects of XIDs >= xmax. It can see
+	 * the effects of all older XIDs except those listed in the snapshot. xmin
+	 * is stored as an optimization to avoid needing to search the XID arrays
+	 * for most tuples.
+	 */
+	TransactionId xmin;			/* all XID < xmin are visible to me */
+	TransactionId xmax;			/* all XID >= xmax are invisible to me */
+	TransactionId *xip;			/* array of xact IDs in progress */
+	uint32		xcnt;			/* # of xact ids in xip[] */
+	/* note: all ids in xip[] satisfy xmin <= xip[i] < xmax */
+	int32		subxcnt;		/* # of xact ids in subxip[] */
+	TransactionId *subxip;		/* array of subxact IDs in progress */
+	bool		suboverflowed;	/* has the subxip array overflowed? */
+	bool		takenDuringRecovery;	/* recovery-shaped snapshot? */
+	bool		copied;			/* false if it's a static snapshot */
+
+	/*
+	 * note: all ids in subxip[] are >= xmin, but we don't bother filtering
+	 * out any that are >= xmax
+	 */
+	CommandId	curcid;			/* in my xact, CID < curcid are visible */
+	uint32		active_count;	/* refcount on ActiveSnapshot stack */
+	uint32		regd_count;		/* refcount on RegisteredSnapshotList */
+} SnapshotData;
+
+/*
+ * Result codes for HeapTupleSatisfiesUpdate.  This should really be in
+ * tqual.h, but we want to avoid including that file elsewhere.
+ */
+typedef enum
+{
+	HeapTupleMayBeUpdated,
+	HeapTupleInvisible,
+	HeapTupleSelfUpdated,
+	HeapTupleUpdated,
+	HeapTupleBeingUpdated
+} HTSU_Result;
+
+#endif   /* SNAPSHOT_H */