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) 1996-2021, 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
 *
 *      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.
 * ----------------
 */
IndexTuple
index_form_tuple(TupleDesc tupleDescriptor,
                 Datum *values,
                 bool *isnull)
{
    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];
    bool        untoasted_free[INDEX_MAX_KEYS];
#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((struct 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 = toast_compress_datum(untoasted_values[i]);

            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 *) palloc0(size);
    tuple = (IndexTuple) tp;

    heap_fill_tuple(tupleDescriptor,
#ifdef TOAST_INDEX_HACK
                    untoasted_values,
#else
                    values,
#endif
                    isnull,
                    (char *) tp + hoff,
                    data_size,
                    &tupmask,
                    (hasnull ? (bits8 *) 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.
 *
 *      This caches attribute offsets in the attribute descriptor.
 *
 *      An alternative way to speed things up would be to cache offsets
 *      with the tuple, but that seems more difficult unless you take
 *      the storage hit of actually putting those offsets into the
 *      tuple you send to disk.  Yuck.
 *
 *      This scheme will be slightly slower than that, but should
 *      perform well for queries which hit large #'s of tuples.  After
 *      you cache the offsets once, examining all the other tuples using
 *      the same attribute descriptor will go much quicker. -cim 5/4/91
 * ----------------
 */
Datum
nocache_index_getattr(IndexTuple tup,
                      int attnum,
                      TupleDesc tupleDesc)
{
    char       *tp;             /* ptr to data part of tuple */
    bits8      *bp = NULL;      /* ptr to null bitmap in tuple */
    bool        slow = false;   /* do we have to walk attrs? */
    int         data_off;       /* tuple data offset */
    int         off;            /* current offset within data */

    /* ----------------
     *   Three cases:
     *
     *   1: No nulls and no variable-width attributes.
     *   2: Has a null or a var-width AFTER att.
     *   3: Has nulls or var-widths BEFORE att.
     * ----------------
     */

    data_off = IndexInfoFindDataOffset(tup->t_info);

    attnum--;

    if (IndexTupleHasNulls(tup))
    {
        /*
         * there's a null somewhere in the tuple
         *
         * check to see if desired att is null
         */

        /* XXX "knows" t_bits are just after fixed tuple header! */
        bp = (bits8 *) ((char *) tup + sizeof(IndexTupleData));

        /*
         * Now check to see if any preceding bits are null...
         */
        {
            int         byte = attnum >> 3;
            int         finalbit = attnum & 0x07;

            /* check for nulls "before" final bit of last byte */
            if ((~bp[byte]) & ((1 << finalbit) - 1))
                slow = true;
            else
            {
                /* check for nulls in any "earlier" bytes */
                int         i;

                for (i = 0; i < byte; i++)
                {
                    if (bp[i] != 0xFF)
                    {
                        slow = true;
                        break;
                    }
                }
            }
        }
    }

    tp = (char *) tup + data_off;

    if (!slow)
    {
        Form_pg_attribute att;

        /*
         * If we get here, there are no nulls up to and including the target
         * attribute.  If we have a cached offset, we can use it.
         */
        att = TupleDescAttr(tupleDesc, attnum);
        if (att->attcacheoff >= 0)
            return fetchatt(att, tp + att->attcacheoff);

        /*
         * Otherwise, check for non-fixed-length attrs up to and including
         * target.  If there aren't any, it's safe to cheaply initialize the
         * cached offsets for these attrs.
         */
        if (IndexTupleHasVarwidths(tup))
        {
            int         j;

            for (j = 0; j <= attnum; j++)
            {
                if (TupleDescAttr(tupleDesc, j)->attlen <= 0)
                {
                    slow = true;
                    break;
                }
            }
        }
    }

    if (!slow)
    {
        int         natts = tupleDesc->natts;
        int         j = 1;

        /*
         * If we get here, we have a tuple with no nulls or var-widths up to
         * and including the target attribute, so we can use the cached offset
         * ... only we don't have it yet, or we'd not have got here.  Since
         * it's cheap to compute offsets for fixed-width columns, we take the
         * opportunity to initialize the cached offsets for *all* the leading
         * fixed-width columns, in hope of avoiding future visits to this
         * routine.
         */
        TupleDescAttr(tupleDesc, 0)->attcacheoff = 0;

        /* we might have set some offsets in the slow path previously */
        while (j < natts && TupleDescAttr(tupleDesc, j)->attcacheoff > 0)
            j++;

        off = TupleDescAttr(tupleDesc, j - 1)->attcacheoff +
            TupleDescAttr(tupleDesc, j - 1)->attlen;

        for (; j < natts; j++)
        {
            Form_pg_attribute att = TupleDescAttr(tupleDesc, j);

            if (att->attlen <= 0)
                break;

            off = att_align_nominal(off, att->attalign);

            att->attcacheoff = off;

            off += att->attlen;
        }

        Assert(j > attnum);

        off = TupleDescAttr(tupleDesc, attnum)->attcacheoff;
    }
    else
    {
        bool        usecache = true;
        int         i;

        /*
         * Now we know that we have to walk the tuple CAREFULLY.  But we still
         * might be able to cache some offsets for next time.
         *
         * Note - This loop is a little tricky.  For each non-null attribute,
         * we have to first account for alignment padding before the attr,
         * then advance over the attr based on its length.  Nulls have no
         * storage and no alignment padding either.  We can use/set
         * attcacheoff until we reach either a null or a var-width attribute.
         */
        off = 0;
        for (i = 0;; i++)       /* loop exit is at "break" */
        {
            Form_pg_attribute att = TupleDescAttr(tupleDesc, i);

            if (IndexTupleHasNulls(tup) && att_isnull(i, bp))
            {
                usecache = false;
                continue;       /* this cannot be the target att */
            }

            /* If we know the next offset, we can skip the rest */
            if (usecache && att->attcacheoff >= 0)
                off = att->attcacheoff;
            else if (att->attlen == -1)
            {
                /*
                 * We can only cache the offset for a varlena attribute if the
                 * offset is already suitably aligned, so that there would be
                 * no pad bytes in any case: then the offset will be valid for
                 * either an aligned or unaligned value.
                 */
                if (usecache &&
                    off == att_align_nominal(off, att->attalign))
                    att->attcacheoff = off;
                else
                {
                    off = att_align_pointer(off, att->attalign, -1,
                                            tp + off);
                    usecache = false;
                }
            }
            else
            {
                /* not varlena, so safe to use att_align_nominal */
                off = att_align_nominal(off, att->attalign);

                if (usecache)
                    att->attcacheoff = off;
            }

            if (i == attnum)
                break;

            off = att_addlength_pointer(off, att->attlen, tp + off);

            if (usecache && att->attlen <= 0)
                usecache = false;
        }
    }

    return fetchatt(TupleDescAttr(tupleDesc, attnum), 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)
{
    int         hasnulls = IndexTupleHasNulls(tup);
    int         natts = tupleDescriptor->natts; /* number of atts to extract */
    int         attnum;
    char       *tp;             /* ptr to tuple data */
    int         off;            /* offset in tuple data */
    bits8      *bp;             /* ptr to null bitmap in tuple */
    bool        slow = false;   /* can we use/set attcacheoff? */

    /* Assert to protect callers who allocate fixed-size arrays */
    Assert(natts <= INDEX_MAX_KEYS);

    /* XXX "knows" t_bits are just after fixed tuple header! */
    bp = (bits8 *) ((char *) tup + sizeof(IndexTupleData));

    tp = (char *) tup + IndexInfoFindDataOffset(tup->t_info);
    off = 0;

    for (attnum = 0; attnum < natts; attnum++)
    {
        Form_pg_attribute thisatt = TupleDescAttr(tupleDescriptor, attnum);

        if (hasnulls && att_isnull(attnum, bp))
        {
            values[attnum] = (Datum) 0;
            isnull[attnum] = true;
            slow = true;        /* can't use attcacheoff anymore */
            continue;
        }

        isnull[attnum] = false;

        if (!slow && thisatt->attcacheoff >= 0)
            off = thisatt->attcacheoff;
        else if (thisatt->attlen == -1)
        {
            /*
             * We can only cache the offset for a varlena attribute if the
             * offset is already suitably aligned, so that there would be no
             * pad bytes in any case: then the offset will be valid for either
             * an aligned or unaligned value.
             */
            if (!slow &&
                off == att_align_nominal(off, thisatt->attalign))
                thisatt->attcacheoff = off;
            else
            {
                off = att_align_pointer(off, thisatt->attalign, -1,
                                        tp + off);
                slow = true;
            }
        }
        else
        {
            /* not varlena, so safe to use att_align_nominal */
            off = att_align_nominal(off, thisatt->attalign);

            if (!slow)
                thisatt->attcacheoff = off;
        }

        values[attnum] = fetchatt(thisatt, tp + off);

        off = att_addlength_pointer(off, thisatt->attlen, tp + off);

        if (thisatt->attlen <= 0)
            slow = true;        /* can't use attcacheoff anymore */
    }
}

/*
 * 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 descriptor to scribble on */
    truncdesc = palloc(TupleDescSize(sourceDescriptor));
    TupleDescCopy(truncdesc, sourceDescriptor);
    truncdesc->natts = 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;
}