indextuple.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * indextuple.c
 *     This file contains index tuple accessor and mutator routines,
 *     as well as various tuple utilities.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/access/common/indextuple.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/detoast.h"
#include "access/heaptoast.h"
#include "access/htup_details.h"
#include "access/itup.h"
#include "access/toast_internals.h"
 
/*
 * This enables de-toasting of index entries.  Needed until VACUUM is
 * smart enough to rebuild indexes from scratch.
 */
#define TOAST_INDEX_HACK
 
/* ----------------------------------------------------------------
 *                index_ tuple interface routines
 * ----------------------------------------------------------------
 */
 
 /* ----------------
  *     index_form_tuple
  *
  *     As index_form_tuple_context, but allocates the returned tuple in the
  *     CurrentMemoryContext.
  * ----------------
  */
IndexTuple
index_form_tuple(TupleDesc tupleDescriptor,
                 const Datum *values,
                 const bool *isnull)
{
    return index_form_tuple_context(tupleDescriptor, values, isnull,
                                    CurrentMemoryContext);
}
 
/* ----------------
 *      index_form_tuple_context
 *
 *      This shouldn't leak any memory; otherwise, callers such as
 *      tuplesort_putindextuplevalues() will be very unhappy.
 *
 *      This shouldn't perform external table access provided caller
 *      does not pass values that are stored EXTERNAL.
 *
 *      Allocates returned tuple in provided 'context'.
 * ----------------
 */
IndexTuple
index_form_tuple_context(TupleDesc tupleDescriptor,
                         const Datum *values,
                         const bool *isnull,
                         MemoryContext context)
{
    char       *tp;             /* tuple pointer */
    IndexTuple  tuple;          /* return tuple */
    Size        size,
                data_size,
                hoff;
    int         i;
    unsigned short infomask = 0;
    bool        hasnull = false;
    uint16      tupmask = 0;
    int         numberOfAttributes = tupleDescriptor->natts;
 
#ifdef TOAST_INDEX_HACK
    Datum       untoasted_values[INDEX_MAX_KEYS] = {0};
    bool        untoasted_free[INDEX_MAX_KEYS] = {0};
#endif
 
    if (numberOfAttributes > INDEX_MAX_KEYS)
        ereport(ERROR,
                (errcode(ERRCODE_TOO_MANY_COLUMNS),
                 errmsg("number of index columns (%d) exceeds limit (%d)",
                        numberOfAttributes, INDEX_MAX_KEYS)));
 
#ifdef TOAST_INDEX_HACK
    for (i = 0; i < numberOfAttributes; i++)
    {
        Form_pg_attribute att = TupleDescAttr(tupleDescriptor, i);
 
        untoasted_values[i] = values[i];
        untoasted_free[i] = false;
 
        /* Do nothing if value is NULL or not of varlena type */
        if (isnull[i] || att->attlen != -1)
            continue;
 
        /*
         * If value is stored EXTERNAL, must fetch it so we are not depending
         * on outside storage.  This should be improved someday.
         */
        if (VARATT_IS_EXTERNAL(DatumGetPointer(values[i])))
        {
            untoasted_values[i] =
                PointerGetDatum(detoast_external_attr((varlena *)
                                                      DatumGetPointer(values[i])));
            untoasted_free[i] = true;
        }
 
        /*
         * If value is above size target, and is of a compressible datatype,
         * try to compress it in-line.
         */
        if (!VARATT_IS_EXTENDED(DatumGetPointer(untoasted_values[i])) &&
            VARSIZE(DatumGetPointer(untoasted_values[i])) > TOAST_INDEX_TARGET &&
            (att->attstorage == TYPSTORAGE_EXTENDED ||
             att->attstorage == TYPSTORAGE_MAIN))
        {
            Datum       cvalue;
 
            cvalue = toast_compress_datum(untoasted_values[i],
                                          att->attcompression);
 
            if (DatumGetPointer(cvalue) != NULL)
            {
                /* successful compression */
                if (untoasted_free[i])
                    pfree(DatumGetPointer(untoasted_values[i]));
                untoasted_values[i] = cvalue;
                untoasted_free[i] = true;
            }
        }
    }
#endif
 
    for (i = 0; i < numberOfAttributes; i++)
    {
        if (isnull[i])
        {
            hasnull = true;
            break;
        }
    }
 
    if (hasnull)
        infomask |= INDEX_NULL_MASK;
 
    hoff = IndexInfoFindDataOffset(infomask);
#ifdef TOAST_INDEX_HACK
    data_size = heap_compute_data_size(tupleDescriptor,
                                       untoasted_values, isnull);
#else
    data_size = heap_compute_data_size(tupleDescriptor,
                                       values, isnull);
#endif
    size = hoff + data_size;
    size = MAXALIGN(size);      /* be conservative */
 
    tp = (char *) MemoryContextAllocZero(context, size);
    tuple = (IndexTuple) tp;
 
    heap_fill_tuple(tupleDescriptor,
#ifdef TOAST_INDEX_HACK
                    untoasted_values,
#else
                    values,
#endif
                    isnull,
                    tp + hoff,
                    data_size,
                    &tupmask,
                    (hasnull ? (uint8 *) tp + sizeof(IndexTupleData) : NULL));
 
#ifdef TOAST_INDEX_HACK
    for (i = 0; i < numberOfAttributes; i++)
    {
        if (untoasted_free[i])
            pfree(DatumGetPointer(untoasted_values[i]));
    }
#endif
 
    /*
     * We do this because heap_fill_tuple wants to initialize a "tupmask"
     * which is used for HeapTuples, but we want an indextuple infomask. The
     * only relevant info is the "has variable attributes" field. We have
     * already set the hasnull bit above.
     */
    if (tupmask & HEAP_HASVARWIDTH)
        infomask |= INDEX_VAR_MASK;
 
    /* Also assert we got rid of external attributes */
#ifdef TOAST_INDEX_HACK
    Assert((tupmask & HEAP_HASEXTERNAL) == 0);
#endif
 
    /*
     * Here we make sure that the size will fit in the field reserved for it
     * in t_info.
     */
    if ((size & INDEX_SIZE_MASK) != size)
        ereport(ERROR,
                (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
                 errmsg("index row requires %zu bytes, maximum size is %zu",
                        size, (Size) INDEX_SIZE_MASK)));
 
    infomask |= size;
 
    /*
     * initialize metadata
     */
    tuple->t_info = infomask;
    return tuple;
}
 
/* ----------------
 *      nocache_index_getattr
 *
 *      This gets called from index_getattr() macro, and only in cases
 *      where we can't use cacheoffset and the value is not null.
 * ----------------
 */
Datum
nocache_index_getattr(IndexTuple tup,
                      int attnum,
                      TupleDesc tupleDesc)
{
    CompactAttribute *cattr;
    char       *tp;             /* ptr to data part of tuple */
    uint8      *bp = NULL;      /* ptr to null bitmap in tuple */
    int         data_off;       /* tuple data offset */
    int         off;            /* current offset within data */
    int         startAttr;
    int         firstNullAttr;
    bool        hasnulls = IndexTupleHasNulls(tup);
    int         i;
 
    /* Did someone forget to call TupleDescFinalize()? */
    Assert(tupleDesc->firstNonCachedOffsetAttr >= 0);
 
    attnum--;
 
    data_off = IndexInfoFindDataOffset(tup->t_info);
    tp = (char *) tup + data_off;
 
    /*
     * To minimize the number of attributes we need to look at, start walking
     * the tuple at the attribute with the highest attcacheoff prior to attnum
     * or the first NULL attribute prior to attnum, whichever comes first.
     */
    if (hasnulls)
    {
        bp = (uint8 *) ((char *) tup + sizeof(IndexTupleData));
        firstNullAttr = first_null_attr(bp, attnum);
    }
    else
        firstNullAttr = attnum;
 
    if (tupleDesc->firstNonCachedOffsetAttr > 0 && firstNullAttr > 0)
    {
        /*
         * Try to start with the highest attribute with an attcacheoff that's
         * prior to the one we're looking for, or with the attribute prior to
         * the first NULL attribute, if there is one.
         */
        startAttr = Min(tupleDesc->firstNonCachedOffsetAttr - 1, firstNullAttr - 1);
        off = TupleDescCompactAttr(tupleDesc, startAttr)->attcacheoff;
    }
    else
    {
        /* Otherwise, start at the beginning... */
        startAttr = 0;
        off = 0;
    }
 
    /*
     * Calculate 'off' up to the first NULL attr.  We use two cheaper loops
     * when the tuple has no variable-width columns.  When variable-width
     * columns exists, we use att_addlength_pointer() to move the offset
     * beyond the current attribute.
     */
    if (IndexTupleHasVarwidths(tup))
    {
        /* Calculate the offset up until the first NULL */
        for (i = startAttr; i < firstNullAttr; i++)
        {
            cattr = TupleDescCompactAttr(tupleDesc, i);
 
            off = att_pointer_alignby(off,
                                      cattr->attalignby,
                                      cattr->attlen,
                                      tp + off);
            off = att_addlength_pointer(off, cattr->attlen, tp + off);
        }
 
        /* Calculate the offset for any remaining columns. */
        for (; i < attnum; i++)
        {
            Assert(hasnulls);
 
            if (att_isnull(i, bp))
                continue;
 
            cattr = TupleDescCompactAttr(tupleDesc, i);
 
            off = att_pointer_alignby(off,
                                      cattr->attalignby,
                                      cattr->attlen,
                                      tp + off);
            off = att_addlength_pointer(off, cattr->attlen, tp + off);
        }
    }
    else
    {
        /* Handle tuples with only fixed-width attributes */
 
        /* Calculate the offset up until the first NULL */
        for (i = startAttr; i < firstNullAttr; i++)
        {
            cattr = TupleDescCompactAttr(tupleDesc, i);
 
            Assert(cattr->attlen > 0);
            off = att_nominal_alignby(off, cattr->attalignby);
            off += cattr->attlen;
        }
 
        /* Calculate the offset for any remaining columns. */
        for (; i < attnum; i++)
        {
            Assert(hasnulls);
 
            if (att_isnull(i, bp))
                continue;
 
            cattr = TupleDescCompactAttr(tupleDesc, i);
 
            Assert(cattr->attlen > 0);
            off = att_nominal_alignby(off, cattr->attalignby);
            off += cattr->attlen;
        }
    }
 
    cattr = TupleDescCompactAttr(tupleDesc, attnum);
    off = att_pointer_alignby(off, cattr->attalignby,
                              cattr->attlen, tp + off);
    return fetchatt(cattr, tp + off);
}
 
/*
 * Convert an index tuple into Datum/isnull arrays.
 *
 * The caller must allocate sufficient storage for the output arrays.
 * (INDEX_MAX_KEYS entries should be enough.)
 *
 * This is nearly the same as heap_deform_tuple(), but for IndexTuples.
 * One difference is that the tuple should never have any missing columns.
 */
void
index_deform_tuple(IndexTuple tup, TupleDesc tupleDescriptor,
                   Datum *values, bool *isnull)
{
    char       *tp;             /* ptr to tuple data */
    uint8      *bp;             /* ptr to null bitmap in tuple */
 
    /* XXX "knows" t_bits are just after fixed tuple header! */
    bp = (uint8 *) ((char *) tup + sizeof(IndexTupleData));
 
    tp = (char *) tup + IndexInfoFindDataOffset(tup->t_info);
 
    index_deform_tuple_internal(tupleDescriptor, values, isnull,
                                tp, bp, IndexTupleHasNulls(tup));
}
 
/*
 * Convert an index tuple into Datum/isnull arrays,
 * without assuming any specific layout of the index tuple header.
 *
 * Caller must supply pointer to data area, pointer to nulls bitmap
 * (which can be NULL if !hasnulls), and hasnulls flag.
 */
void
index_deform_tuple_internal(TupleDesc tupleDescriptor,
                            Datum *values, bool *isnull,
                            char *tp, uint8 *bp, int hasnulls)
{
    CompactAttribute *cattr;
    int         natts = tupleDescriptor->natts; /* number of atts to extract */
    int         attnum = 0;
    uint32      off = 0;        /* offset in tuple data */
    int         firstNonCacheOffsetAttr;
    int         firstNullAttr;
 
    /* Assert to protect callers who allocate fixed-size arrays */
    Assert(natts <= INDEX_MAX_KEYS);
 
    /* Did someone forget to call TupleDescFinalize()? */
    Assert(tupleDescriptor->firstNonCachedOffsetAttr >= 0);
 
    firstNonCacheOffsetAttr = Min(tupleDescriptor->firstNonCachedOffsetAttr, natts);
 
    if (hasnulls)
    {
        firstNullAttr = first_null_attr(bp, natts);
        firstNonCacheOffsetAttr = Min(firstNonCacheOffsetAttr, firstNullAttr);
    }
    else
        firstNullAttr = natts;
 
    if (firstNonCacheOffsetAttr > 0)
    {
#ifdef USE_ASSERT_CHECKING
        /* In Assert enabled builds, verify attcacheoff is correct */
        off = 0;
#endif
 
        do
        {
            isnull[attnum] = false;
            cattr = TupleDescCompactAttr(tupleDescriptor, attnum);
 
#ifdef USE_ASSERT_CHECKING
            off = att_nominal_alignby(off, cattr->attalignby);
            Assert(off == cattr->attcacheoff);
            off += cattr->attlen;
#endif
 
            values[attnum] = fetch_att_noerr(tp + cattr->attcacheoff, cattr->attbyval,
                                             cattr->attlen);
        } while (++attnum < firstNonCacheOffsetAttr);
 
        off = cattr->attcacheoff + cattr->attlen;
    }
 
    for (; attnum < firstNullAttr; attnum++)
    {
        isnull[attnum] = false;
        cattr = TupleDescCompactAttr(tupleDescriptor, attnum);
 
        /* align 'off', fetch the datum, and increment off beyond the datum */
        values[attnum] = align_fetch_then_add(tp,
                                              &off,
                                              cattr->attbyval,
                                              cattr->attlen,
                                              cattr->attalignby);
    }
 
    for (; attnum < natts; attnum++)
    {
        Assert(hasnulls);
 
        if (att_isnull(attnum, bp))
        {
            values[attnum] = (Datum) 0;
            isnull[attnum] = true;
            continue;
        }
 
        isnull[attnum] = false;
        cattr = TupleDescCompactAttr(tupleDescriptor, attnum);
 
        /* align 'off', fetch the attr's value, and increment off beyond it */
        values[attnum] = align_fetch_then_add(tp,
                                              &off,
                                              cattr->attbyval,
                                              cattr->attlen,
                                              cattr->attalignby);
    }
}
 
/*
 * Create a palloc'd copy of an index tuple.
 */
IndexTuple
CopyIndexTuple(IndexTuple source)
{
    IndexTuple  result;
    Size        size;
 
    size = IndexTupleSize(source);
    result = (IndexTuple) palloc(size);
    memcpy(result, source, size);
    return result;
}
 
/*
 * Create a palloc'd copy of an index tuple, leaving only the first
 * leavenatts attributes remaining.
 *
 * Truncation is guaranteed to result in an index tuple that is no
 * larger than the original.  It is safe to use the IndexTuple with
 * the original tuple descriptor, but caller must avoid actually
 * accessing truncated attributes from returned tuple!  In practice
 * this means that index_getattr() must be called with special care,
 * and that the truncated tuple should only ever be accessed by code
 * under caller's direct control.
 *
 * It's safe to call this function with a buffer lock held, since it
 * never performs external table access.  If it ever became possible
 * for index tuples to contain EXTERNAL TOAST values, then this would
 * have to be revisited.
 */
IndexTuple
index_truncate_tuple(TupleDesc sourceDescriptor, IndexTuple source,
                     int leavenatts)
{
    TupleDesc   truncdesc;
    Datum       values[INDEX_MAX_KEYS];
    bool        isnull[INDEX_MAX_KEYS];
    IndexTuple  truncated;
 
    Assert(leavenatts <= sourceDescriptor->natts);
 
    /* Easy case: no truncation actually required */
    if (leavenatts == sourceDescriptor->natts)
        return CopyIndexTuple(source);
 
    /* Create temporary truncated tuple descriptor */
    truncdesc = CreateTupleDescTruncatedCopy(sourceDescriptor, leavenatts);
 
    /* Deform, form copy of tuple with fewer attributes */
    index_deform_tuple(source, truncdesc, values, isnull);
    truncated = index_form_tuple(truncdesc, values, isnull);
    truncated->t_tid = source->t_tid;
    Assert(IndexTupleSize(truncated) <= IndexTupleSize(source));
 
    /*
     * Cannot leak memory here, TupleDescCopy() doesn't allocate any inner
     * structure, so, plain pfree() should clean all allocated memory
     */
    pfree(truncdesc);
 
    return truncated;
}