itup.h

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/*-------------------------------------------------------------------------
 *
 * itup.h
 *    POSTGRES index tuple definitions.
 *
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/itup.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef ITUP_H
#define ITUP_H
 
#include "access/tupdesc.h"
#include "access/tupmacs.h"
#include "storage/bufpage.h"
#include "storage/itemptr.h"
 
/*
 * Index tuple header structure
 *
 * All index tuples start with IndexTupleData.  If the HasNulls bit is set,
 * this is followed by an IndexAttributeBitMapData.  The index attribute
 * values follow, beginning at a MAXALIGN boundary.
 *
 * Note that the space allocated for the bitmap does not vary with the number
 * of attributes; that is because we don't have room to store the number of
 * attributes in the header.  Given the MAXALIGN constraint there's no space
 * savings to be had anyway, for usual values of INDEX_MAX_KEYS.
 */
 
typedef struct IndexTupleData
{
    ItemPointerData t_tid;      /* reference TID to heap tuple */
 
    /* ---------------
     * t_info is laid out in the following fashion:
     *
     * 15th (high) bit: has nulls
     * 14th bit: has var-width attributes
     * 13th bit: AM-defined meaning
     * 12-0 bit: size of tuple
     * ---------------
     */
 
    unsigned short t_info;      /* various info about tuple */
 
} IndexTupleData;               /* MORE DATA FOLLOWS AT END OF STRUCT */
 
typedef IndexTupleData *IndexTuple;
 
typedef struct IndexAttributeBitMapData
{
    bits8       bits[(INDEX_MAX_KEYS + 8 - 1) / 8];
}           IndexAttributeBitMapData;
 
typedef IndexAttributeBitMapData * IndexAttributeBitMap;
 
/*
 * t_info manipulation macros
 */
#define INDEX_SIZE_MASK 0x1FFF
#define INDEX_AM_RESERVED_BIT 0x2000    /* reserved for index-AM specific
                                         * usage */
#define INDEX_VAR_MASK  0x4000
#define INDEX_NULL_MASK 0x8000
 
static inline Size
IndexTupleSize(const IndexTupleData *itup)
{
    return (itup->t_info & INDEX_SIZE_MASK);
}
 
static inline bool
IndexTupleHasNulls(const IndexTupleData *itup)
{
    return itup->t_info & INDEX_NULL_MASK;
}
 
static inline bool
IndexTupleHasVarwidths(const IndexTupleData *itup)
{
    return itup->t_info & INDEX_VAR_MASK;
}
 
 
/* routines in indextuple.c */
extern IndexTuple index_form_tuple(TupleDesc tupleDescriptor,
                                   const Datum *values, const bool *isnull);
extern IndexTuple index_form_tuple_context(TupleDesc tupleDescriptor,
                                           const Datum *values, const bool *isnull,
                                           MemoryContext context);
extern Datum nocache_index_getattr(IndexTuple tup, int attnum,
                                   TupleDesc tupleDesc);
extern void index_deform_tuple(IndexTuple tup, TupleDesc tupleDescriptor,
                               Datum *values, bool *isnull);
extern void index_deform_tuple_internal(TupleDesc tupleDescriptor,
                                        Datum *values, bool *isnull,
                                        char *tp, bits8 *bp, int hasnulls);
extern IndexTuple CopyIndexTuple(IndexTuple source);
extern IndexTuple index_truncate_tuple(TupleDesc sourceDescriptor,
                                       IndexTuple source, int leavenatts);
 
 
/*
 * Takes an infomask as argument (primarily because this needs to be usable
 * at index_form_tuple time so enough space is allocated).
 */
static inline Size
IndexInfoFindDataOffset(unsigned short t_info)
{
    if (!(t_info & INDEX_NULL_MASK))
        return MAXALIGN(sizeof(IndexTupleData));
    else
        return MAXALIGN(sizeof(IndexTupleData) + sizeof(IndexAttributeBitMapData));
}
 
#ifndef FRONTEND
 
/* ----------------
 *      index_getattr
 *
 *      This gets called many times, so we macro the cacheable and NULL
 *      lookups, and call nocache_index_getattr() for the rest.
 *
 * ----------------
 */
static inline Datum
index_getattr(IndexTuple tup, int attnum, TupleDesc tupleDesc, bool *isnull)
{
    Assert(PointerIsValid(isnull));
    Assert(attnum > 0);
 
    *isnull = false;
 
    if (!IndexTupleHasNulls(tup))
    {
        CompactAttribute *attr = TupleDescCompactAttr(tupleDesc, attnum - 1);
 
        if (attr->attcacheoff >= 0)
        {
            return fetchatt(attr,
                            (char *) tup + IndexInfoFindDataOffset(tup->t_info) +
                            attr->attcacheoff);
        }
        else
            return nocache_index_getattr(tup, attnum, tupleDesc);
    }
    else
    {
        if (att_isnull(attnum - 1, (bits8 *) tup + sizeof(IndexTupleData)))
        {
            *isnull = true;
            return (Datum) NULL;
        }
        else
            return nocache_index_getattr(tup, attnum, tupleDesc);
    }
}
 
#endif
 
/*
 * MaxIndexTuplesPerPage is an upper bound on the number of tuples that can
 * fit on one index page.  An index tuple must have either data or a null
 * bitmap, so we can safely assume it's at least 1 byte bigger than a bare
 * IndexTupleData struct.  We arrive at the divisor because each tuple
 * must be maxaligned, and it must have an associated line pointer.
 *
 * To be index-type-independent, this does not account for any special space
 * on the page, and is thus conservative.
 *
 * Note: in btree non-leaf pages, the first tuple has no key (it's implicitly
 * minus infinity), thus breaking the "at least 1 byte bigger" assumption.
 * On such a page, N tuples could take one MAXALIGN quantum less space than
 * estimated here, seemingly allowing one more tuple than estimated here.
 * But such a page always has at least MAXALIGN special space, so we're safe.
 */
#define MaxIndexTuplesPerPage   \
    ((int) ((BLCKSZ - SizeOfPageHeaderData) / \
            (MAXALIGN(sizeof(IndexTupleData) + 1) + sizeof(ItemIdData))))
 
#endif                          /* ITUP_H */