postgresql/src/include/executor/tuptable.h

/*-------------------------------------------------------------------------
 *
 * tuptable.h
 *	  tuple table support stuff
 *
 *
 * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/include/executor/tuptable.h,v 1.30 2006/03/05 15:58:56 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#ifndef TUPTABLE_H
#define TUPTABLE_H

#include "access/htup.h"


/*----------
 * The executor stores tuples in a "tuple table" which is composed of
 * independent TupleTableSlots.  There are several cases we need to handle:
 *		1. physical tuple in a disk buffer page
 *		2. physical tuple constructed in palloc'ed memory
 *		3. "virtual" tuple consisting of Datum/isnull arrays
 *
 * The first two cases are similar in that they both deal with "materialized"
 * tuples, but resource management is different.  For a tuple in a disk page
 * we need to hold a pin on the buffer until the TupleTableSlot's reference
 * to the tuple is dropped; while for a palloc'd tuple we usually want the
 * tuple pfree'd when the TupleTableSlot's reference is dropped.
 *
 * A "virtual" tuple is an optimization used to minimize physical data
 * copying in a nest of plan nodes.  Any pass-by-reference Datums in the
 * tuple point to storage that is not directly associated with the
 * TupleTableSlot; generally they will point to part of a tuple stored in
 * a lower plan node's output TupleTableSlot, or to a function result
 * constructed in a plan node's per-tuple econtext.  It is the responsibility
 * of the generating plan node to be sure these resources are not released
 * for as long as the virtual tuple needs to be valid.	We only use virtual
 * tuples in the result slots of plan nodes --- tuples to be copied anywhere
 * else need to be "materialized" into physical tuples.  Note also that a
 * virtual tuple does not have any "system columns".
 *
 * The Datum/isnull arrays of a TupleTableSlot serve double duty.  When the
 * slot contains a virtual tuple, they are the authoritative data.	When the
 * slot contains a physical tuple, the arrays contain data extracted from
 * the tuple.  (In this state, any pass-by-reference Datums point into
 * the physical tuple.)  The extracted information is built "lazily",
 * ie, only as needed.	This serves to avoid repeated extraction of data
 * from the physical tuple.
 *
 * A TupleTableSlot can also be "empty", holding no valid data.  This is
 * the only valid state for a freshly-created slot that has not yet had a
 * tuple descriptor assigned to it.  In this state, tts_isempty must be
 * TRUE, tts_shouldFree FALSE, tts_tuple NULL, tts_buffer InvalidBuffer,
 * and tts_nvalid zero.
 *
 * When tts_shouldFree is true, the physical tuple is "owned" by the slot
 * and should be freed when the slot's reference to the tuple is dropped.
 *
 * tts_shouldFreeDesc is similar to tts_shouldFree: if it's true, then the
 * tupleDescriptor is "owned" by the TupleTableSlot and should be
 * freed when the slot's reference to the descriptor is dropped.
 *
 * If tts_buffer is not InvalidBuffer, then the slot is holding a pin
 * on the indicated buffer page; drop the pin when we release the
 * slot's reference to that buffer.  (tts_shouldFree should always be
 * false in such a case, since presumably tts_tuple is pointing at the
 * buffer page.)
 *
 * tts_nvalid indicates the number of valid columns in the tts_values/isnull
 * arrays.	When the slot is holding a "virtual" tuple this must be equal
 * to the descriptor's natts.  When the slot is holding a physical tuple
 * this is equal to the number of columns we have extracted (we always
 * extract columns from left to right, so there are no holes).
 *
 * tts_values/tts_isnull are allocated when a descriptor is assigned to the
 * slot; they are of length equal to the descriptor's natts.
 *
 * tts_slow/tts_off are saved state for slot_deform_tuple, and should not
 * be touched by any other code.
 *----------
 */
typedef struct TupleTableSlot
{
	NodeTag		type;			/* vestigial ... allows IsA tests */
	bool		tts_isempty;	/* true = slot is empty */
	bool		tts_shouldFree; /* should pfree tuple? */
	bool		tts_shouldFreeDesc;		/* should pfree descriptor? */
	bool		tts_slow;		/* saved state for slot_deform_tuple */
	HeapTuple	tts_tuple;		/* physical tuple, or NULL if none */
	TupleDesc	tts_tupleDescriptor;	/* slot's tuple descriptor */
	MemoryContext tts_mcxt;		/* slot itself is in this context */
	Buffer		tts_buffer;		/* tuple's buffer, or InvalidBuffer */
	int			tts_nvalid;		/* # of valid values in tts_values */
	Datum	   *tts_values;		/* current per-attribute values */
	bool	   *tts_isnull;		/* current per-attribute isnull flags */
	long		tts_off;		/* saved state for slot_deform_tuple */
} TupleTableSlot;

/*
 * Tuple table data structure: an array of TupleTableSlots.
 */
typedef struct TupleTableData
{
	int			size;			/* size of the table (number of slots) */
	int			next;			/* next available slot number */
	TupleTableSlot array[1];	/* VARIABLE LENGTH ARRAY - must be last */
} TupleTableData;				/* VARIABLE LENGTH STRUCT */

typedef TupleTableData *TupleTable;


/*
 * TupIsNull -- is a TupleTableSlot empty?
 */
#define TupIsNull(slot) \
	((slot) == NULL || (slot)->tts_isempty)

/* in executor/execTuples.c */
extern TupleTable ExecCreateTupleTable(int tableSize);
extern void ExecDropTupleTable(TupleTable table, bool shouldFree);
extern TupleTableSlot *MakeSingleTupleTableSlot(TupleDesc tupdesc);
extern void ExecDropSingleTupleTableSlot(TupleTableSlot *slot);
extern TupleTableSlot *ExecAllocTableSlot(TupleTable table);
extern void ExecSetSlotDescriptor(TupleTableSlot *slot,
					  TupleDesc tupdesc, bool shouldFree);
extern TupleTableSlot *ExecStoreTuple(HeapTuple tuple,
			   TupleTableSlot *slot,
			   Buffer buffer,
			   bool shouldFree);
extern TupleTableSlot *ExecClearTuple(TupleTableSlot *slot);
extern TupleTableSlot *ExecStoreVirtualTuple(TupleTableSlot *slot);
extern TupleTableSlot *ExecStoreAllNullTuple(TupleTableSlot *slot);
extern HeapTuple ExecCopySlotTuple(TupleTableSlot *slot);
extern HeapTuple ExecFetchSlotTuple(TupleTableSlot *slot);
extern HeapTuple ExecMaterializeSlot(TupleTableSlot *slot);
extern TupleTableSlot *ExecCopySlot(TupleTableSlot *dstslot,
			 TupleTableSlot *srcslot);

/* in access/common/heaptuple.c */
extern Datum slot_getattr(TupleTableSlot *slot, int attnum, bool *isnull);
extern void slot_getallattrs(TupleTableSlot *slot);
extern void slot_getsomeattrs(TupleTableSlot *slot, int attnum);
extern bool slot_attisnull(TupleTableSlot *slot, int attnum);

#endif   /* TUPTABLE_H */