90 lines
3.2 KiB
C
90 lines
3.2 KiB
C
/*-------------------------------------------------------------------------
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*
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* htup.h
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* POSTGRES heap tuple definitions.
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*
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*
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* Portions Copyright (c) 1996-2024, 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/access/htup.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef HTUP_H
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#define HTUP_H
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#include "storage/itemptr.h"
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/* typedefs and forward declarations for structs defined in htup_details.h */
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typedef struct HeapTupleHeaderData HeapTupleHeaderData;
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typedef HeapTupleHeaderData *HeapTupleHeader;
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typedef struct MinimalTupleData MinimalTupleData;
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typedef MinimalTupleData *MinimalTuple;
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/*
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* HeapTupleData is an in-memory data structure that points to a tuple.
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*
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* There are several ways in which this data structure is used:
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*
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* * Pointer to a tuple in a disk buffer: t_data points directly into the
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* buffer (which the code had better be holding a pin on, but this is not
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* reflected in HeapTupleData itself).
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*
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* * Pointer to nothing: t_data is NULL. This is used as a failure indication
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* in some functions.
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*
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* * Part of a palloc'd tuple: the HeapTupleData itself and the tuple
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* form a single palloc'd chunk. t_data points to the memory location
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* immediately following the HeapTupleData struct (at offset HEAPTUPLESIZE).
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* This is the output format of heap_form_tuple and related routines.
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*
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* * Separately allocated tuple: t_data points to a palloc'd chunk that
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* is not adjacent to the HeapTupleData. (This case is deprecated since
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* it's difficult to tell apart from case #1. It should be used only in
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* limited contexts where the code knows that case #1 will never apply.)
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*
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* * Separately allocated minimal tuple: t_data points MINIMAL_TUPLE_OFFSET
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* bytes before the start of a MinimalTuple. As with the previous case,
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* this can't be told apart from case #1 by inspection; code setting up
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* or destroying this representation has to know what it's doing.
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*
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* t_len should always be valid, except in the pointer-to-nothing case.
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* t_self and t_tableOid should be valid if the HeapTupleData points to
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* a disk buffer, or if it represents a copy of a tuple on disk. They
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* should be explicitly set invalid in manufactured tuples.
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*/
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typedef struct HeapTupleData
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{
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uint32 t_len; /* length of *t_data */
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ItemPointerData t_self; /* SelfItemPointer */
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Oid t_tableOid; /* table the tuple came from */
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#define FIELDNO_HEAPTUPLEDATA_DATA 3
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HeapTupleHeader t_data; /* -> tuple header and data */
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} HeapTupleData;
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typedef HeapTupleData *HeapTuple;
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#define HEAPTUPLESIZE MAXALIGN(sizeof(HeapTupleData))
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/*
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* Accessor macros to be used with HeapTuple pointers.
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*/
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#define HeapTupleIsValid(tuple) PointerIsValid(tuple)
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/* HeapTupleHeader functions implemented in utils/time/combocid.c */
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extern CommandId HeapTupleHeaderGetCmin(HeapTupleHeader tup);
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extern CommandId HeapTupleHeaderGetCmax(HeapTupleHeader tup);
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extern void HeapTupleHeaderAdjustCmax(HeapTupleHeader tup,
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CommandId *cmax, bool *iscombo);
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/* Prototype for HeapTupleHeader accessors in heapam.c */
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extern TransactionId HeapTupleGetUpdateXid(HeapTupleHeader tuple);
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#endif /* HTUP_H */
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