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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 */
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