brin_tuple.c

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/*
 * brin_tuple.c
 *      Method implementations for tuples in BRIN indexes.
 *
 * Intended usage is that code outside this file only deals with
 * BrinMemTuples, and convert to and from the on-disk representation through
 * functions in this file.
 *
 * NOTES
 *
 * A BRIN tuple is similar to a heap tuple, with a few key differences.  The
 * first interesting difference is that the tuple header is much simpler, only
 * containing its total length and a small area for flags.  Also, the stored
 * data does not match the relation tuple descriptor exactly: for each
 * attribute in the descriptor, the index tuple carries an arbitrary number
 * of values, depending on the opclass.
 *
 * Also, for each column of the index relation there are two null bits: one
 * (hasnulls) stores whether any tuple within the page range has that column
 * set to null; the other one (allnulls) stores whether the column values are
 * all null.  If allnulls is true, then the tuple data area does not contain
 * values for that column at all; whereas it does if the hasnulls is set.
 * Note the size of the null bitmask may not be the same as that of the
 * datum array.
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/access/brin/brin_tuple.c
 */
#include "postgres.h"

#include "access/brin_tuple.h"
#include "access/detoast.h"
#include "access/heaptoast.h"
#include "access/htup_details.h"
#include "access/toast_internals.h"
#include "access/tupdesc.h"
#include "access/tupmacs.h"
#include "utils/datum.h"
#include "utils/memutils.h"


/*
 * This enables de-toasting of index entries.  Needed until VACUUM is
 * smart enough to rebuild indexes from scratch.
 */
#define TOAST_INDEX_HACK


static inline void brin_deconstruct_tuple(BrinDesc *brdesc,
                                          char *tp, bits8 *nullbits, bool nulls,
                                          Datum *values, bool *allnulls, bool *hasnulls);


/*
 * Return a tuple descriptor used for on-disk storage of BRIN tuples.
 */
static TupleDesc
brtuple_disk_tupdesc(BrinDesc *brdesc)
{
    /* We cache these in the BrinDesc */
    if (brdesc->bd_disktdesc == NULL)
    {
        int         i;
        int         j;
        AttrNumber  attno = 1;
        TupleDesc   tupdesc;
        MemoryContext oldcxt;

        /* make sure it's in the bdesc's context */
        oldcxt = MemoryContextSwitchTo(brdesc->bd_context);

        tupdesc = CreateTemplateTupleDesc(brdesc->bd_totalstored);

        for (i = 0; i < brdesc->bd_tupdesc->natts; i++)
        {
            for (j = 0; j < brdesc->bd_info[i]->oi_nstored; j++)
                TupleDescInitEntry(tupdesc, attno++, NULL,
                                   brdesc->bd_info[i]->oi_typcache[j]->type_id,
                                   -1, 0);
        }

        MemoryContextSwitchTo(oldcxt);

        brdesc->bd_disktdesc = tupdesc;
    }

    return brdesc->bd_disktdesc;
}

/*
 * Generate a new on-disk tuple to be inserted in a BRIN index.
 *
 * See brin_form_placeholder_tuple if you touch this.
 */
BrinTuple *
brin_form_tuple(BrinDesc *brdesc, BlockNumber blkno, BrinMemTuple *tuple,
                Size *size)
{
    Datum      *values;
    bool       *nulls;
    bool        anynulls = false;
    BrinTuple  *rettuple;
    int         keyno;
    int         idxattno;
    uint16      phony_infomask = 0;
    bits8      *phony_nullbitmap;
    Size        len,
                hoff,
                data_len;
    int         i;

#ifdef TOAST_INDEX_HACK
    Datum      *untoasted_values;
    int         nuntoasted = 0;
#endif

    Assert(brdesc->bd_totalstored > 0);

    values = (Datum *) palloc(sizeof(Datum) * brdesc->bd_totalstored);
    nulls = (bool *) palloc0(sizeof(bool) * brdesc->bd_totalstored);
    phony_nullbitmap = (bits8 *)
        palloc(sizeof(bits8) * BITMAPLEN(brdesc->bd_totalstored));

#ifdef TOAST_INDEX_HACK
    untoasted_values = (Datum *) palloc(sizeof(Datum) * brdesc->bd_totalstored);
#endif

    /*
     * Set up the values/nulls arrays for heap_fill_tuple
     */
    idxattno = 0;
    for (keyno = 0; keyno < brdesc->bd_tupdesc->natts; keyno++)
    {
        int         datumno;

        /*
         * "allnulls" is set when there's no nonnull value in any row in the
         * column; when this happens, there is no data to store.  Thus set the
         * nullable bits for all data elements of this column and we're done.
         */
        if (tuple->bt_columns[keyno].bv_allnulls)
        {
            for (datumno = 0;
                 datumno < brdesc->bd_info[keyno]->oi_nstored;
                 datumno++)
                nulls[idxattno++] = true;
            anynulls = true;
            continue;
        }

        /*
         * The "hasnulls" bit is set when there are some null values in the
         * data.  We still need to store a real value, but the presence of
         * this means we need a null bitmap.
         */
        if (tuple->bt_columns[keyno].bv_hasnulls)
            anynulls = true;

        /*
         * Now obtain the values of each stored datum.  Note that some values
         * might be toasted, and we cannot rely on the original heap values
         * sticking around forever, so we must detoast them.  Also try to
         * compress them.
         */
        for (datumno = 0;
             datumno < brdesc->bd_info[keyno]->oi_nstored;
             datumno++)
        {
            Datum value = tuple->bt_columns[keyno].bv_values[datumno];

#ifdef TOAST_INDEX_HACK

            /* We must look at the stored type, not at the index descriptor. */
            TypeCacheEntry  *atttype = brdesc->bd_info[keyno]->oi_typcache[datumno];

            /* Do we need to free the value at the end? */
            bool free_value = false;

            /* For non-varlena types we don't need to do anything special */
            if (atttype->typlen != -1)
            {
                values[idxattno++] = value;
                continue;
            }

            /*
             * Do nothing if value is not of varlena type. We don't need to
             * care about NULL values here, thanks to bv_allnulls above.
             *
             * If value is stored EXTERNAL, must fetch it so we are not
             * depending on outside storage.
             *
             * XXX Is this actually true? Could it be that the summary is
             * NULL even for range with non-NULL data? E.g. degenerate bloom
             * filter may be thrown away, etc.
             */
            if (VARATT_IS_EXTERNAL(DatumGetPointer(value)))
            {
                value = PointerGetDatum(detoast_external_attr((struct varlena *)
                                                              DatumGetPointer(value)));
                free_value = true;
            }

            /*
             * If value is above size target, and is of a compressible datatype,
             * try to compress it in-line.
             */
            if (!VARATT_IS_EXTENDED(DatumGetPointer(value)) &&
                VARSIZE(DatumGetPointer(value)) > TOAST_INDEX_TARGET &&
                (atttype->typstorage == TYPSTORAGE_EXTENDED ||
                 atttype->typstorage == TYPSTORAGE_MAIN))
            {
                Datum       cvalue = toast_compress_datum(value);

                if (DatumGetPointer(cvalue) != NULL)
                {
                    /* successful compression */
                    if (free_value)
                        pfree(DatumGetPointer(value));

                    value = cvalue;
                    free_value = true;
                }
            }

            /*
             * If we untoasted / compressed the value, we need to free it
             * after forming the index tuple.
             */
            if (free_value)
                untoasted_values[nuntoasted++] = value;

#endif

            values[idxattno++] = value;
        }
    }

    /* Assert we did not overrun temp arrays */
    Assert(idxattno <= brdesc->bd_totalstored);

    /* compute total space needed */
    len = SizeOfBrinTuple;
    if (anynulls)
    {
        /*
         * We need a double-length bitmap on an on-disk BRIN index tuple; the
         * first half stores the "allnulls" bits, the second stores
         * "hasnulls".
         */
        len += BITMAPLEN(brdesc->bd_tupdesc->natts * 2);
    }

    len = hoff = MAXALIGN(len);

    data_len = heap_compute_data_size(brtuple_disk_tupdesc(brdesc),
                                      values, nulls);
    len += data_len;

    len = MAXALIGN(len);

    rettuple = palloc0(len);
    rettuple->bt_blkno = blkno;
    rettuple->bt_info = hoff;

    /* Assert that hoff fits in the space available */
    Assert((rettuple->bt_info & BRIN_OFFSET_MASK) == hoff);

    /*
     * The infomask and null bitmap as computed by heap_fill_tuple are useless
     * to us.  However, that function will not accept a null infomask; and we
     * need to pass a valid null bitmap so that it will correctly skip
     * outputting null attributes in the data area.
     */
    heap_fill_tuple(brtuple_disk_tupdesc(brdesc),
                    values,
                    nulls,
                    (char *) rettuple + hoff,
                    data_len,
                    &phony_infomask,
                    phony_nullbitmap);

    /* done with these */
    pfree(values);
    pfree(nulls);
    pfree(phony_nullbitmap);

#ifdef TOAST_INDEX_HACK
    for (i = 0; i < nuntoasted; i++)
        pfree(DatumGetPointer(untoasted_values[i]));
#endif

    /*
     * Now fill in the real null bitmasks.  allnulls first.
     */
    if (anynulls)
    {
        bits8      *bitP;
        int         bitmask;

        rettuple->bt_info |= BRIN_NULLS_MASK;

        /*
         * Note that we reverse the sense of null bits in this module: we
         * store a 1 for a null attribute rather than a 0.  So we must reverse
         * the sense of the att_isnull test in brin_deconstruct_tuple as well.
         */
        bitP = ((bits8 *) ((char *) rettuple + SizeOfBrinTuple)) - 1;
        bitmask = HIGHBIT;
        for (keyno = 0; keyno < brdesc->bd_tupdesc->natts; keyno++)
        {
            if (bitmask != HIGHBIT)
                bitmask <<= 1;
            else
            {
                bitP += 1;
                *bitP = 0x0;
                bitmask = 1;
            }

            if (!tuple->bt_columns[keyno].bv_allnulls)
                continue;

            *bitP |= bitmask;
        }
        /* hasnulls bits follow */
        for (keyno = 0; keyno < brdesc->bd_tupdesc->natts; keyno++)
        {
            if (bitmask != HIGHBIT)
                bitmask <<= 1;
            else
            {
                bitP += 1;
                *bitP = 0x0;
                bitmask = 1;
            }

            if (!tuple->bt_columns[keyno].bv_hasnulls)
                continue;

            *bitP |= bitmask;
        }
    }

    if (tuple->bt_placeholder)
        rettuple->bt_info |= BRIN_PLACEHOLDER_MASK;

    *size = len;
    return rettuple;
}

/*
 * Generate a new on-disk tuple with no data values, marked as placeholder.
 *
 * This is a cut-down version of brin_form_tuple.
 */
BrinTuple *
brin_form_placeholder_tuple(BrinDesc *brdesc, BlockNumber blkno, Size *size)
{
    Size        len;
    Size        hoff;
    BrinTuple  *rettuple;
    int         keyno;
    bits8      *bitP;
    int         bitmask;

    /* compute total space needed: always add nulls */
    len = SizeOfBrinTuple;
    len += BITMAPLEN(brdesc->bd_tupdesc->natts * 2);
    len = hoff = MAXALIGN(len);

    rettuple = palloc0(len);
    rettuple->bt_blkno = blkno;
    rettuple->bt_info = hoff;
    rettuple->bt_info |= BRIN_NULLS_MASK | BRIN_PLACEHOLDER_MASK;

    bitP = ((bits8 *) ((char *) rettuple + SizeOfBrinTuple)) - 1;
    bitmask = HIGHBIT;
    /* set allnulls true for all attributes */
    for (keyno = 0; keyno < brdesc->bd_tupdesc->natts; keyno++)
    {
        if (bitmask != HIGHBIT)
            bitmask <<= 1;
        else
        {
            bitP += 1;
            *bitP = 0x0;
            bitmask = 1;
        }

        *bitP |= bitmask;
    }
    /* no need to set hasnulls */

    *size = len;
    return rettuple;
}

/*
 * Free a tuple created by brin_form_tuple
 */
void
brin_free_tuple(BrinTuple *tuple)
{
    pfree(tuple);
}

/*
 * Given a brin tuple of size len, create a copy of it.  If 'dest' is not
 * NULL, its size is destsz, and can be used as output buffer; if the tuple
 * to be copied does not fit, it is enlarged by repalloc, and the size is
 * updated to match.  This avoids palloc/free cycles when many brin tuples
 * are being processed in loops.
 */
BrinTuple *
brin_copy_tuple(BrinTuple *tuple, Size len, BrinTuple *dest, Size *destsz)
{
    if (!destsz || *destsz == 0)
        dest = palloc(len);
    else if (len > *destsz)
    {
        dest = repalloc(dest, len);
        *destsz = len;
    }

    memcpy(dest, tuple, len);

    return dest;
}

/*
 * Return whether two BrinTuples are bitwise identical.
 */
bool
brin_tuples_equal(const BrinTuple *a, Size alen, const BrinTuple *b, Size blen)
{
    if (alen != blen)
        return false;
    if (memcmp(a, b, alen) != 0)
        return false;
    return true;
}

/*
 * Create a new BrinMemTuple from scratch, and initialize it to an empty
 * state.
 *
 * Note: we don't provide any means to free a deformed tuple, so make sure to
 * use a temporary memory context.
 */
BrinMemTuple *
brin_new_memtuple(BrinDesc *brdesc)
{
    BrinMemTuple *dtup;
    long        basesize;

    basesize = MAXALIGN(sizeof(BrinMemTuple) +
                        sizeof(BrinValues) * brdesc->bd_tupdesc->natts);
    dtup = palloc0(basesize + sizeof(Datum) * brdesc->bd_totalstored);

    dtup->bt_values = palloc(sizeof(Datum) * brdesc->bd_totalstored);
    dtup->bt_allnulls = palloc(sizeof(bool) * brdesc->bd_tupdesc->natts);
    dtup->bt_hasnulls = palloc(sizeof(bool) * brdesc->bd_tupdesc->natts);

    dtup->bt_context = AllocSetContextCreate(CurrentMemoryContext,
                                             "brin dtuple",
                                             ALLOCSET_DEFAULT_SIZES);

    brin_memtuple_initialize(dtup, brdesc);

    return dtup;
}

/*
 * Reset a BrinMemTuple to initial state.  We return the same tuple, for
 * notational convenience.
 */
BrinMemTuple *
brin_memtuple_initialize(BrinMemTuple *dtuple, BrinDesc *brdesc)
{
    int         i;
    char       *currdatum;

    MemoryContextReset(dtuple->bt_context);

    currdatum = (char *) dtuple +
        MAXALIGN(sizeof(BrinMemTuple) +
                 sizeof(BrinValues) * brdesc->bd_tupdesc->natts);
    for (i = 0; i < brdesc->bd_tupdesc->natts; i++)
    {
        dtuple->bt_columns[i].bv_attno = i + 1;
        dtuple->bt_columns[i].bv_allnulls = true;
        dtuple->bt_columns[i].bv_hasnulls = false;
        dtuple->bt_columns[i].bv_values = (Datum *) currdatum;
        currdatum += sizeof(Datum) * brdesc->bd_info[i]->oi_nstored;
    }

    return dtuple;
}

/*
 * Convert a BrinTuple back to a BrinMemTuple.  This is the reverse of
 * brin_form_tuple.
 *
 * As an optimization, the caller can pass a previously allocated 'dMemtuple'.
 * This avoids having to allocate it here, which can be useful when this
 * function is called many times in a loop.  It is caller's responsibility
 * that the given BrinMemTuple matches what we need here.
 *
 * Note we don't need the "on disk tupdesc" here; we rely on our own routine to
 * deconstruct the tuple from the on-disk format.
 */
BrinMemTuple *
brin_deform_tuple(BrinDesc *brdesc, BrinTuple *tuple, BrinMemTuple *dMemtuple)
{
    BrinMemTuple *dtup;
    Datum      *values;
    bool       *allnulls;
    bool       *hasnulls;
    char       *tp;
    bits8      *nullbits;
    int         keyno;
    int         valueno;
    MemoryContext oldcxt;

    dtup = dMemtuple ? brin_memtuple_initialize(dMemtuple, brdesc) :
        brin_new_memtuple(brdesc);

    if (BrinTupleIsPlaceholder(tuple))
        dtup->bt_placeholder = true;
    dtup->bt_blkno = tuple->bt_blkno;

    values = dtup->bt_values;
    allnulls = dtup->bt_allnulls;
    hasnulls = dtup->bt_hasnulls;

    tp = (char *) tuple + BrinTupleDataOffset(tuple);

    if (BrinTupleHasNulls(tuple))
        nullbits = (bits8 *) ((char *) tuple + SizeOfBrinTuple);
    else
        nullbits = NULL;
    brin_deconstruct_tuple(brdesc,
                           tp, nullbits, BrinTupleHasNulls(tuple),
                           values, allnulls, hasnulls);

    /*
     * Iterate to assign each of the values to the corresponding item in the
     * values array of each column.  The copies occur in the tuple's context.
     */
    oldcxt = MemoryContextSwitchTo(dtup->bt_context);
    for (valueno = 0, keyno = 0; keyno < brdesc->bd_tupdesc->natts; keyno++)
    {
        int         i;

        if (allnulls[keyno])
        {
            valueno += brdesc->bd_info[keyno]->oi_nstored;
            continue;
        }

        /*
         * We would like to skip datumCopy'ing the values datum in some cases,
         * caller permitting ...
         */
        for (i = 0; i < brdesc->bd_info[keyno]->oi_nstored; i++)
            dtup->bt_columns[keyno].bv_values[i] =
                datumCopy(values[valueno++],
                          brdesc->bd_info[keyno]->oi_typcache[i]->typbyval,
                          brdesc->bd_info[keyno]->oi_typcache[i]->typlen);

        dtup->bt_columns[keyno].bv_hasnulls = hasnulls[keyno];
        dtup->bt_columns[keyno].bv_allnulls = false;
    }

    MemoryContextSwitchTo(oldcxt);

    return dtup;
}

/*
 * brin_deconstruct_tuple
 *      Guts of attribute extraction from an on-disk BRIN tuple.
 *
 * Its arguments are:
 *  brdesc      BRIN descriptor for the stored tuple
 *  tp          pointer to the tuple data area
 *  nullbits    pointer to the tuple nulls bitmask
 *  nulls       "has nulls" bit in tuple infomask
 *  values      output values, array of size brdesc->bd_totalstored
 *  allnulls    output "allnulls", size brdesc->bd_tupdesc->natts
 *  hasnulls    output "hasnulls", size brdesc->bd_tupdesc->natts
 *
 * Output arrays must have been allocated by caller.
 */
static inline void
brin_deconstruct_tuple(BrinDesc *brdesc,
                       char *tp, bits8 *nullbits, bool nulls,
                       Datum *values, bool *allnulls, bool *hasnulls)
{
    int         attnum;
    int         stored;
    TupleDesc   diskdsc;
    long        off;

    /*
     * First iterate to natts to obtain both null flags for each attribute.
     * Note that we reverse the sense of the att_isnull test, because we store
     * 1 for a null value (rather than a 1 for a not null value as is the
     * att_isnull convention used elsewhere.)  See brin_form_tuple.
     */
    for (attnum = 0; attnum < brdesc->bd_tupdesc->natts; attnum++)
    {
        /*
         * the "all nulls" bit means that all values in the page range for
         * this column are nulls.  Therefore there are no values in the tuple
         * data area.
         */
        allnulls[attnum] = nulls && !att_isnull(attnum, nullbits);

        /*
         * the "has nulls" bit means that some tuples have nulls, but others
         * have not-null values.  Therefore we know the tuple contains data
         * for this column.
         *
         * The hasnulls bits follow the allnulls bits in the same bitmask.
         */
        hasnulls[attnum] =
            nulls && !att_isnull(brdesc->bd_tupdesc->natts + attnum, nullbits);
    }

    /*
     * Iterate to obtain each attribute's stored values.  Note that since we
     * may reuse attribute entries for more than one column, we cannot cache
     * offsets here.
     */
    diskdsc = brtuple_disk_tupdesc(brdesc);
    stored = 0;
    off = 0;
    for (attnum = 0; attnum < brdesc->bd_tupdesc->natts; attnum++)
    {
        int         datumno;

        if (allnulls[attnum])
        {
            stored += brdesc->bd_info[attnum]->oi_nstored;
            continue;
        }

        for (datumno = 0;
             datumno < brdesc->bd_info[attnum]->oi_nstored;
             datumno++)
        {
            Form_pg_attribute thisatt = TupleDescAttr(diskdsc, stored);

            if (thisatt->attlen == -1)
            {
                off = att_align_pointer(off, thisatt->attalign, -1,
                                        tp + off);
            }
            else
            {
                /* not varlena, so safe to use att_align_nominal */
                off = att_align_nominal(off, thisatt->attalign);
            }

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

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