htup.h

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/*-------------------------------------------------------------------------
 *
 * htup.h
 *    POSTGRES heap tuple definitions.
 *
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/htup.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef HTUP_H
#define HTUP_H

#include "storage/itemptr.h"

/* typedefs and forward declarations for structs defined in htup_details.h */

typedef struct HeapTupleHeaderData HeapTupleHeaderData;

typedef HeapTupleHeaderData *HeapTupleHeader;

typedef struct MinimalTupleData MinimalTupleData;

typedef MinimalTupleData *MinimalTuple;


/*
 * HeapTupleData is an in-memory data structure that points to a tuple.
 *
 * There are several ways in which this data structure is used:
 *
 * * Pointer to a tuple in a disk buffer: t_data points directly into the
 *   buffer (which the code had better be holding a pin on, but this is not
 *   reflected in HeapTupleData itself).
 *
 * * Pointer to nothing: t_data is NULL.  This is used as a failure indication
 *   in some functions.
 *
 * * Part of a palloc'd tuple: the HeapTupleData itself and the tuple
 *   form a single palloc'd chunk.  t_data points to the memory location
 *   immediately following the HeapTupleData struct (at offset HEAPTUPLESIZE).
 *   This is the output format of heap_form_tuple and related routines.
 *
 * * Separately allocated tuple: t_data points to a palloc'd chunk that
 *   is not adjacent to the HeapTupleData.  (This case is deprecated since
 *   it's difficult to tell apart from case #1.  It should be used only in
 *   limited contexts where the code knows that case #1 will never apply.)
 *
 * * Separately allocated minimal tuple: t_data points MINIMAL_TUPLE_OFFSET
 *   bytes before the start of a MinimalTuple.  As with the previous case,
 *   this can't be told apart from case #1 by inspection; code setting up
 *   or destroying this representation has to know what it's doing.
 *
 * t_len should always be valid, except in the pointer-to-nothing case.
 * t_self and t_tableOid should be valid if the HeapTupleData points to
 * a disk buffer, or if it represents a copy of a tuple on disk.  They
 * should be explicitly set invalid in manufactured tuples.
 */
typedef struct HeapTupleData
{
    uint32      t_len;          /* length of *t_data */
    ItemPointerData t_self;     /* SelfItemPointer */
    Oid         t_tableOid;     /* table the tuple came from */
#define FIELDNO_HEAPTUPLEDATA_DATA 3
    HeapTupleHeader t_data;     /* -> tuple header and data */
} HeapTupleData;

typedef HeapTupleData *HeapTuple;

#define HEAPTUPLESIZE   MAXALIGN(sizeof(HeapTupleData))

/*
 * Accessor macros to be used with HeapTuple pointers.
 */
#define HeapTupleIsValid(tuple) PointerIsValid(tuple)

/* HeapTupleHeader functions implemented in utils/time/combocid.c */
extern CommandId HeapTupleHeaderGetCmin(HeapTupleHeader tup);
extern CommandId HeapTupleHeaderGetCmax(HeapTupleHeader tup);
extern void HeapTupleHeaderAdjustCmax(HeapTupleHeader tup,
                                      CommandId *cmax, bool *iscombo);

/* Prototype for HeapTupleHeader accessors in heapam.c */
extern TransactionId HeapTupleGetUpdateXid(HeapTupleHeader tuple);

#endif                          /* HTUP_H */