Force a checkpoint in CREATE DATABASE before starting to copy the files,

[PostgreSQL.git] / src / backend / access / common / heaptuple.c

/*-------------------------------------------------------------------------
 *
 * heaptuple.c
 *        This file contains heap tuple accessor and mutator routines, as well
 *        as various tuple utilities.
 *
 * NOTE: there is massive duplication of code in this module to
 * support both the convention that a null is marked by a bool TRUE,
 * and the convention that a null is marked by a char 'n'.      The latter
 * convention is deprecated but it'll probably be a long time before
 * we can get rid of it entirely.
 *
 *
 * Some notes about varlenas and this code:
 *
 * Before Postgres 8.3 varlenas always had a 4-byte length header, and
 * therefore always needed 4-byte alignment (at least).  This wasted space
 * for short varlenas, for example CHAR(1) took 5 bytes and could need up to
 * 3 additional padding bytes for alignment.
 *
 * Now, a short varlena (up to 126 data bytes) is reduced to a 1-byte header
 * and we don't align it.  To hide this from datatype-specific functions that
 * don't want to deal with it, such a datum is considered "toasted" and will
 * be expanded back to the normal 4-byte-header format by pg_detoast_datum.
 * (In performance-critical code paths we can use pg_detoast_datum_packed
 * and the appropriate access macros to avoid that overhead.)  Note that this
 * conversion is performed directly in heap_form_tuple (or heap_formtuple),
 * without explicitly invoking the toaster.
 *
 * This change will break any code that assumes it needn't detoast values
 * that have been put into a tuple but never sent to disk.      Hopefully there
 * are few such places.
 *
 * Varlenas still have alignment 'i' (or 'd') in pg_type/pg_attribute, since
 * that's the normal requirement for the untoasted format.  But we ignore that
 * for the 1-byte-header format.  This means that the actual start position
 * of a varlena datum may vary depending on which format it has.  To determine
 * what is stored, we have to require that alignment padding bytes be zero.
 * (Postgres actually has always zeroed them, but now it's required!)  Since
 * the first byte of a 1-byte-header varlena can never be zero, we can examine
 * the first byte after the previous datum to tell if it's a pad byte or the
 * start of a 1-byte-header varlena.
 *
 * Note that while formerly we could rely on the first varlena column of a
 * system catalog to be at the offset suggested by the C struct for the
 * catalog, this is now risky: it's only safe if the preceding field is
 * word-aligned, so that there will never be any padding.
 *
 * We don't pack varlenas whose attstorage is 'p', since the data type
 * isn't expecting to have to detoast values.  This is used in particular
 * by oidvector and int2vector, which are used in the system catalogs
 * and we'd like to still refer to them via C struct offsets.
 *
 *
 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *        $PostgreSQL$
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/heapam.h"
#include "access/sysattr.h"
#include "access/tuptoaster.h"
#include "executor/tuptable.h"


/* Does att's datatype allow packing into the 1-byte-header varlena format? */
#define ATT_IS_PACKABLE(att) \
        ((att)->attlen == -1 && (att)->attstorage != 'p')
/* Use this if it's already known varlena */
#define VARLENA_ATT_IS_PACKABLE(att) \
        ((att)->attstorage != 'p')


/* ----------------------------------------------------------------
 *                                              misc support routines
 * ----------------------------------------------------------------
 */


/*
 * heap_compute_data_size
 *              Determine size of the data area of a tuple to be constructed
 */
Size
heap_compute_data_size(TupleDesc tupleDesc,
                                           Datum *values,
                                           bool *isnull)
{
        Size            data_length = 0;
        int                     i;
        int                     numberOfAttributes = tupleDesc->natts;
        Form_pg_attribute *att = tupleDesc->attrs;

        for (i = 0; i < numberOfAttributes; i++)
        {
                Datum           val;

                if (isnull[i])
                        continue;

                val = values[i];

                if (ATT_IS_PACKABLE(att[i]) &&
                        VARATT_CAN_MAKE_SHORT(DatumGetPointer(val)))
                {
                        /*
                         * we're anticipating converting to a short varlena header, so
                         * adjust length and don't count any alignment
                         */
                        data_length += VARATT_CONVERTED_SHORT_SIZE(DatumGetPointer(val));
                }
                else
                {
                        data_length = att_align_datum(data_length, att[i]->attalign,
                                                                                  att[i]->attlen, val);
                        data_length = att_addlength_datum(data_length, att[i]->attlen,
                                                                                          val);
                }
        }

        return data_length;
}

/* ----------------
 *              ComputeDataSize
 *
 * Determine size of the data area of a tuple to be constructed
 *
 * OLD API with char 'n'/' ' convention for indicating nulls
 * ----------------
 */
static Size
ComputeDataSize(TupleDesc tupleDesc,
                                Datum *values,
                                char *nulls)
{
        Size            data_length = 0;
        int                     i;
        int                     numberOfAttributes = tupleDesc->natts;
        Form_pg_attribute *att = tupleDesc->attrs;

        for (i = 0; i < numberOfAttributes; i++)
        {
                Datum           val;

                if (nulls[i] != ' ')
                        continue;

                val = values[i];

                if (ATT_IS_PACKABLE(att[i]) &&
                        VARATT_CAN_MAKE_SHORT(DatumGetPointer(val)))
                {
                        /*
                         * we're anticipating converting to a short varlena header, so
                         * adjust length and don't count any alignment
                         */
                        data_length += VARATT_CONVERTED_SHORT_SIZE(DatumGetPointer(val));
                }
                else
                {
                        data_length = att_align_datum(data_length, att[i]->attalign,
                                                                                  att[i]->attlen, val);
                        data_length = att_addlength_datum(data_length, att[i]->attlen,
                                                                                          val);
                }
        }

        return data_length;
}

/*
 * heap_fill_tuple
 *              Load data portion of a tuple from values/isnull arrays
 *
 * We also fill the null bitmap (if any) and set the infomask bits
 * that reflect the tuple's data contents.
 *
 * NOTE: it is now REQUIRED that the caller have pre-zeroed the data area.
 */
void
heap_fill_tuple(TupleDesc tupleDesc,
                                Datum *values, bool *isnull,
                                char *data, Size data_size,
                                uint16 *infomask, bits8 *bit)
{
        bits8      *bitP;
        int                     bitmask;
        int                     i;
        int                     numberOfAttributes = tupleDesc->natts;
        Form_pg_attribute *att = tupleDesc->attrs;

#ifdef USE_ASSERT_CHECKING
        char       *start = data;
#endif

        if (bit != NULL)
        {
                bitP = &bit[-1];
                bitmask = HIGHBIT;
        }
        else
        {
                /* just to keep compiler quiet */
                bitP = NULL;
                bitmask = 0;
        }

        *infomask &= ~(HEAP_HASNULL | HEAP_HASVARWIDTH | HEAP_HASEXTERNAL);

        for (i = 0; i < numberOfAttributes; i++)
        {
                Size            data_length;

                if (bit != NULL)
                {
                        if (bitmask != HIGHBIT)
                                bitmask <<= 1;
                        else
                        {
                                bitP += 1;
                                *bitP = 0x0;
                                bitmask = 1;
                        }

                        if (isnull[i])
                        {
                                *infomask |= HEAP_HASNULL;
                                continue;
                        }

                        *bitP |= bitmask;
                }

                /*
                 * XXX we use the att_align macros on the pointer value itself, not on
                 * an offset.  This is a bit of a hack.
                 */

                if (att[i]->attbyval)
                {
                        /* pass-by-value */
                        data = (char *) att_align_nominal((long) data, att[i]->attalign);
                        store_att_byval(data, values[i], att[i]->attlen);
                        data_length = att[i]->attlen;
                }
                else if (att[i]->attlen == -1)
                {
                        /* varlena */
                        Pointer         val = DatumGetPointer(values[i]);

                        *infomask |= HEAP_HASVARWIDTH;
                        if (VARATT_IS_EXTERNAL(val))
                        {
                                *infomask |= HEAP_HASEXTERNAL;
                                /* no alignment, since it's short by definition */
                                data_length = VARSIZE_EXTERNAL(val);
                                memcpy(data, val, data_length);
                        }
                        else if (VARATT_IS_SHORT(val))
                        {
                                /* no alignment for short varlenas */
                                data_length = VARSIZE_SHORT(val);
                                memcpy(data, val, data_length);
                        }
                        else if (VARLENA_ATT_IS_PACKABLE(att[i]) &&
                                         VARATT_CAN_MAKE_SHORT(val))
                        {
                                /* convert to short varlena -- no alignment */
                                data_length = VARATT_CONVERTED_SHORT_SIZE(val);
                                SET_VARSIZE_SHORT(data, data_length);
                                memcpy(data + 1, VARDATA(val), data_length - 1);
                        }
                        else
                        {
                                /* full 4-byte header varlena */
                                data = (char *) att_align_nominal((long) data,
                                                                                                  att[i]->attalign);
                                data_length = VARSIZE(val);
                                memcpy(data, val, data_length);
                        }
                }
                else if (att[i]->attlen == -2)
                {
                        /* cstring ... never needs alignment */
                        *infomask |= HEAP_HASVARWIDTH;
                        Assert(att[i]->attalign == 'c');
                        data_length = strlen(DatumGetCString(values[i])) + 1;
                        memcpy(data, DatumGetPointer(values[i]), data_length);
                }
                else
                {
                        /* fixed-length pass-by-reference */
                        data = (char *) att_align_nominal((long) data, att[i]->attalign);
                        Assert(att[i]->attlen > 0);
                        data_length = att[i]->attlen;
                        memcpy(data, DatumGetPointer(values[i]), data_length);
                }

                data += data_length;
        }

        Assert((data - start) == data_size);
}

/* ----------------
 *              DataFill
 *
 * Load data portion of a tuple from values/nulls arrays
 *
 * OLD API with char 'n'/' ' convention for indicating nulls
 * ----------------
 */
static void
DataFill(TupleDesc tupleDesc,
                 Datum *values, char *nulls,
                 char *data, Size data_size,
                 uint16 *infomask, bits8 *bit)
{
        bits8      *bitP;
        int                     bitmask;
        int                     i;
        int                     numberOfAttributes = tupleDesc->natts;
        Form_pg_attribute *att = tupleDesc->attrs;

#ifdef USE_ASSERT_CHECKING
        char       *start = data;
#endif

        if (bit != NULL)
        {
                bitP = &bit[-1];
                bitmask = HIGHBIT;
        }
        else
        {
                /* just to keep compiler quiet */
                bitP = NULL;
                bitmask = 0;
        }

        *infomask &= ~(HEAP_HASNULL | HEAP_HASVARWIDTH | HEAP_HASEXTERNAL);

        for (i = 0; i < numberOfAttributes; i++)
        {
                Size            data_length;

                if (bit != NULL)
                {
                        if (bitmask != HIGHBIT)
                                bitmask <<= 1;
                        else
                        {
                                bitP += 1;
                                *bitP = 0x0;
                                bitmask = 1;
                        }

                        if (nulls[i] == 'n')
                        {
                                *infomask |= HEAP_HASNULL;
                                continue;
                        }

                        *bitP |= bitmask;
                }

                /*
                 * XXX we use the att_align macros on the pointer value itself, not on
                 * an offset.  This is a bit of a hack.
                 */

                if (att[i]->attbyval)
                {
                        /* pass-by-value */
                        data = (char *) att_align_nominal((long) data, att[i]->attalign);
                        store_att_byval(data, values[i], att[i]->attlen);
                        data_length = att[i]->attlen;
                }
                else if (att[i]->attlen == -1)
                {
                        /* varlena */
                        Pointer         val = DatumGetPointer(values[i]);

                        *infomask |= HEAP_HASVARWIDTH;
                        if (VARATT_IS_EXTERNAL(val))
                        {
                                *infomask |= HEAP_HASEXTERNAL;
                                /* no alignment, since it's short by definition */
                                data_length = VARSIZE_EXTERNAL(val);
                                memcpy(data, val, data_length);
                        }
                        else if (VARATT_IS_SHORT(val))
                        {
                                /* no alignment for short varlenas */
                                data_length = VARSIZE_SHORT(val);
                                memcpy(data, val, data_length);
                        }
                        else if (VARLENA_ATT_IS_PACKABLE(att[i]) &&
                                         VARATT_CAN_MAKE_SHORT(val))
                        {
                                /* convert to short varlena -- no alignment */
                                data_length = VARATT_CONVERTED_SHORT_SIZE(val);
                                SET_VARSIZE_SHORT(data, data_length);
                                memcpy(data + 1, VARDATA(val), data_length - 1);
                        }
                        else
                        {
                                /* full 4-byte header varlena */
                                data = (char *) att_align_nominal((long) data,
                                                                                                  att[i]->attalign);
                                data_length = VARSIZE(val);
                                memcpy(data, val, data_length);
                        }
                }
                else if (att[i]->attlen == -2)
                {
                        /* cstring ... never needs alignment */
                        *infomask |= HEAP_HASVARWIDTH;
                        Assert(att[i]->attalign == 'c');
                        data_length = strlen(DatumGetCString(values[i])) + 1;
                        memcpy(data, DatumGetPointer(values[i]), data_length);
                }
                else
                {
                        /* fixed-length pass-by-reference */
                        data = (char *) att_align_nominal((long) data, att[i]->attalign);
                        Assert(att[i]->attlen > 0);
                        data_length = att[i]->attlen;
                        memcpy(data, DatumGetPointer(values[i]), data_length);
                }

                data += data_length;
        }

        Assert((data - start) == data_size);
}

/* ----------------------------------------------------------------
 *                                              heap tuple interface
 * ----------------------------------------------------------------
 */

/* ----------------
 *              heap_attisnull  - returns TRUE iff tuple attribute is not present
 * ----------------
 */
bool
heap_attisnull(HeapTuple tup, int attnum)
{
        if (attnum > (int) HeapTupleHeaderGetNatts(tup->t_data))
                return true;

        if (attnum > 0)
        {
                if (HeapTupleNoNulls(tup))
                        return false;
                return att_isnull(attnum - 1, tup->t_data->t_bits);
        }

        switch (attnum)
        {
                case TableOidAttributeNumber:
                case SelfItemPointerAttributeNumber:
                case ObjectIdAttributeNumber:
                case MinTransactionIdAttributeNumber:
                case MinCommandIdAttributeNumber:
                case MaxTransactionIdAttributeNumber:
                case MaxCommandIdAttributeNumber:
                        /* these are never null */
                        break;

                default:
                        elog(ERROR, "invalid attnum: %d", attnum);
        }

        return false;
}

/* ----------------
 *              nocachegetattr
 *
 *              This only gets called from fastgetattr() macro, in cases where
 *              we can't use a 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
 *
 *              NOTE: if you need to change this code, see also heap_deform_tuple.
 *              Also see nocache_index_getattr, which is the same code for index
 *              tuples.
 * ----------------
 */
Datum
nocachegetattr(HeapTuple tuple,
                           int attnum,
                           TupleDesc tupleDesc,
                           bool *isnull)
{
        HeapTupleHeader tup = tuple->t_data;
        Form_pg_attribute *att = tupleDesc->attrs;
        char       *tp;                         /* ptr to data part of tuple */
        bits8      *bp = tup->t_bits;           /* ptr to null bitmap in tuple */
        bool            slow = false;   /* do we have to walk attrs? */
        int                     off;                    /* current offset within data */

        (void) isnull;                          /* not used */

        /* ----------------
         *       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.
         * ----------------
         */

#ifdef IN_MACRO
/* This is handled in the macro */
        Assert(attnum > 0);

        if (isnull)
                *isnull = false;
#endif

        attnum--;

        if (HeapTupleNoNulls(tuple))
        {
#ifdef IN_MACRO
/* This is handled in the macro */
                if (att[attnum]->attcacheoff >= 0)
                {
                        return fetchatt(att[attnum],
                                                        (char *) tup + tup->t_hoff +
                                                        att[attnum]->attcacheoff);
                }
#endif
        }
        else
        {
                /*
                 * there's a null somewhere in the tuple
                 *
                 * check to see if desired att is null
                 */

#ifdef IN_MACRO
/* This is handled in the macro */
                if (att_isnull(attnum, bp))
                {
                        if (isnull)
                                *isnull = true;
                        return (Datum) NULL;
                }
#endif

                /*
                 * 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 + tup->t_hoff;

        if (!slow)
        {
                /*
                 * 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.
                 */
                if (att[attnum]->attcacheoff >= 0)
                {
                        return fetchatt(att[attnum],
                                                        tp + att[attnum]->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 (HeapTupleHasVarWidth(tuple))
                {
                        int                     j;

                        for (j = 0; j <= attnum; j++)
                        {
                                if (att[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.
                 */
                att[0]->attcacheoff = 0;

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

                off = att[j - 1]->attcacheoff + att[j - 1]->attlen;

                for (; j < natts; j++)
                {
                        if (att[j]->attlen <= 0)
                                break;

                        off = att_align_nominal(off, att[j]->attalign);

                        att[j]->attcacheoff = off;

                        off += att[j]->attlen;
                }

                Assert(j > attnum);

                off = att[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" */
                {
                        if (HeapTupleHasNulls(tuple) && 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[i]->attcacheoff >= 0)
                                off = att[i]->attcacheoff;
                        else if (att[i]->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[i]->attalign))
                                        att[i]->attcacheoff = off;
                                else
                                {
                                        off = att_align_pointer(off, att[i]->attalign, -1,
                                                                                        tp + off);
                                        usecache = false;
                                }
                        }
                        else
                        {
                                /* not varlena, so safe to use att_align_nominal */
                                off = att_align_nominal(off, att[i]->attalign);

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

                        if (i == attnum)
                                break;

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

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

        return fetchatt(att[attnum], tp + off);
}

/* ----------------
 *              heap_getsysattr
 *
 *              Fetch the value of a system attribute for a tuple.
 *
 * This is a support routine for the heap_getattr macro.  The macro
 * has already determined that the attnum refers to a system attribute.
 * ----------------
 */
Datum
heap_getsysattr(HeapTuple tup, int attnum, TupleDesc tupleDesc, bool *isnull)
{
        Datum           result;

        Assert(tup);

        /* Currently, no sys attribute ever reads as NULL. */
        if (isnull)
                *isnull = false;

        switch (attnum)
        {
                case SelfItemPointerAttributeNumber:
                        /* pass-by-reference datatype */
                        result = PointerGetDatum(&(tup->t_self));
                        break;
                case ObjectIdAttributeNumber:
                        result = ObjectIdGetDatum(HeapTupleGetOid(tup));
                        break;
                case MinTransactionIdAttributeNumber:
                        result = TransactionIdGetDatum(HeapTupleHeaderGetXmin(tup->t_data));
                        break;
                case MaxTransactionIdAttributeNumber:
                        result = TransactionIdGetDatum(HeapTupleHeaderGetXmax(tup->t_data));
                        break;
                case MinCommandIdAttributeNumber:
                case MaxCommandIdAttributeNumber:

                        /*
                         * cmin and cmax are now both aliases for the same field, which
                         * can in fact also be a combo command id.      XXX perhaps we should
                         * return the "real" cmin or cmax if possible, that is if we are
                         * inside the originating transaction?
                         */
                        result = CommandIdGetDatum(HeapTupleHeaderGetRawCommandId(tup->t_data));
                        break;
                case TableOidAttributeNumber:
                        result = ObjectIdGetDatum(tup->t_tableOid);
                        break;
                default:
                        elog(ERROR, "invalid attnum: %d", attnum);
                        result = 0;                     /* keep compiler quiet */
                        break;
        }
        return result;
}

/* ----------------
 *              heap_copytuple
 *
 *              returns a copy of an entire tuple
 *
 * The HeapTuple struct, tuple header, and tuple data are all allocated
 * as a single palloc() block.
 * ----------------
 */
HeapTuple
heap_copytuple(HeapTuple tuple)
{
        HeapTuple       newTuple;

        if (!HeapTupleIsValid(tuple) || tuple->t_data == NULL)
                return NULL;

        newTuple = (HeapTuple) palloc(HEAPTUPLESIZE + tuple->t_len);
        newTuple->t_len = tuple->t_len;
        newTuple->t_self = tuple->t_self;
        newTuple->t_tableOid = tuple->t_tableOid;
        newTuple->t_data = (HeapTupleHeader) ((char *) newTuple + HEAPTUPLESIZE);
        memcpy((char *) newTuple->t_data, (char *) tuple->t_data, tuple->t_len);
        return newTuple;
}

/* ----------------
 *              heap_copytuple_with_tuple
 *
 *              copy a tuple into a caller-supplied HeapTuple management struct
 *
 * Note that after calling this function, the "dest" HeapTuple will not be
 * allocated as a single palloc() block (unlike with heap_copytuple()).
 * ----------------
 */
void
heap_copytuple_with_tuple(HeapTuple src, HeapTuple dest)
{
        if (!HeapTupleIsValid(src) || src->t_data == NULL)
        {
                dest->t_data = NULL;
                return;
        }

        dest->t_len = src->t_len;
        dest->t_self = src->t_self;
        dest->t_tableOid = src->t_tableOid;
        dest->t_data = (HeapTupleHeader) palloc(src->t_len);
        memcpy((char *) dest->t_data, (char *) src->t_data, src->t_len);
}

/*
 * heap_form_tuple
 *              construct a tuple from the given values[] and isnull[] arrays,
 *              which are of the length indicated by tupleDescriptor->natts
 *
 * The result is allocated in the current memory context.
 */
HeapTuple
heap_form_tuple(TupleDesc tupleDescriptor,
                                Datum *values,
                                bool *isnull)
{
        HeapTuple       tuple;                  /* return tuple */
        HeapTupleHeader td;                     /* tuple data */
        Size            len,
                                data_len;
        int                     hoff;
        bool            hasnull = false;
        Form_pg_attribute *att = tupleDescriptor->attrs;
        int                     numberOfAttributes = tupleDescriptor->natts;
        int                     i;

        if (numberOfAttributes > MaxTupleAttributeNumber)
                ereport(ERROR,
                                (errcode(ERRCODE_TOO_MANY_COLUMNS),
                                 errmsg("number of columns (%d) exceeds limit (%d)",
                                                numberOfAttributes, MaxTupleAttributeNumber)));

        /*
         * Check for nulls and embedded tuples; expand any toasted attributes in
         * embedded tuples.  This preserves the invariant that toasting can only
         * go one level deep.
         *
         * We can skip calling toast_flatten_tuple_attribute() if the attribute
         * couldn't possibly be of composite type.  All composite datums are
         * varlena and have alignment 'd'; furthermore they aren't arrays. Also,
         * if an attribute is already toasted, it must have been sent to disk
         * already and so cannot contain toasted attributes.
         */
        for (i = 0; i < numberOfAttributes; i++)
        {
                if (isnull[i])
                        hasnull = true;
                else if (att[i]->attlen == -1 &&
                                 att[i]->attalign == 'd' &&
                                 att[i]->attndims == 0 &&
                                 !VARATT_IS_EXTENDED(DatumGetPointer(values[i])))
                {
                        values[i] = toast_flatten_tuple_attribute(values[i],
                                                                                                          att[i]->atttypid,
                                                                                                          att[i]->atttypmod);
                }
        }

        /*
         * Determine total space needed
         */
        len = offsetof(HeapTupleHeaderData, t_bits);

        if (hasnull)
                len += BITMAPLEN(numberOfAttributes);

        if (tupleDescriptor->tdhasoid)
                len += sizeof(Oid);

        hoff = len = MAXALIGN(len); /* align user data safely */

        data_len = heap_compute_data_size(tupleDescriptor, values, isnull);

        len += data_len;

        /*
         * Allocate and zero the space needed.  Note that the tuple body and
         * HeapTupleData management structure are allocated in one chunk.
         */
        tuple = (HeapTuple) palloc0(HEAPTUPLESIZE + len);
        tuple->t_data = td = (HeapTupleHeader) ((char *) tuple + HEAPTUPLESIZE);

        /*
         * And fill in the information.  Note we fill the Datum fields even though
         * this tuple may never become a Datum.
         */
        tuple->t_len = len;
        ItemPointerSetInvalid(&(tuple->t_self));
        tuple->t_tableOid = InvalidOid;

        HeapTupleHeaderSetDatumLength(td, len);
        HeapTupleHeaderSetTypeId(td, tupleDescriptor->tdtypeid);
        HeapTupleHeaderSetTypMod(td, tupleDescriptor->tdtypmod);

        HeapTupleHeaderSetNatts(td, numberOfAttributes);
        td->t_hoff = hoff;

        if (tupleDescriptor->tdhasoid)          /* else leave infomask = 0 */
                td->t_infomask = HEAP_HASOID;

        heap_fill_tuple(tupleDescriptor,
                                        values,
                                        isnull,
                                        (char *) td + hoff,
                                        data_len,
                                        &td->t_infomask,
                                        (hasnull ? td->t_bits : NULL));

        return tuple;
}

/* ----------------
 *              heap_formtuple
 *
 *              construct a tuple from the given values[] and nulls[] arrays
 *
 *              Null attributes are indicated by a 'n' in the appropriate byte
 *              of nulls[]. Non-null attributes are indicated by a ' ' (space).
 *
 * OLD API with char 'n'/' ' convention for indicating nulls
 * ----------------
 */
HeapTuple
heap_formtuple(TupleDesc tupleDescriptor,
                           Datum *values,
                           char *nulls)
{
        HeapTuple       tuple;                  /* return tuple */
        HeapTupleHeader td;                     /* tuple data */
        Size            len,
                                data_len;
        int                     hoff;
        bool            hasnull = false;
        Form_pg_attribute *att = tupleDescriptor->attrs;
        int                     numberOfAttributes = tupleDescriptor->natts;
        int                     i;

        if (numberOfAttributes > MaxTupleAttributeNumber)
                ereport(ERROR,
                                (errcode(ERRCODE_TOO_MANY_COLUMNS),
                                 errmsg("number of columns (%d) exceeds limit (%d)",
                                                numberOfAttributes, MaxTupleAttributeNumber)));

        /*
         * Check for nulls and embedded tuples; expand any toasted attributes in
         * embedded tuples.  This preserves the invariant that toasting can only
         * go one level deep.
         *
         * We can skip calling toast_flatten_tuple_attribute() if the attribute
         * couldn't possibly be of composite type.  All composite datums are
         * varlena and have alignment 'd'; furthermore they aren't arrays. Also,
         * if an attribute is already toasted, it must have been sent to disk
         * already and so cannot contain toasted attributes.
         */
        for (i = 0; i < numberOfAttributes; i++)
        {
                if (nulls[i] != ' ')
                        hasnull = true;
                else if (att[i]->attlen == -1 &&
                                 att[i]->attalign == 'd' &&
                                 att[i]->attndims == 0 &&
                                 !VARATT_IS_EXTENDED(DatumGetPointer(values[i])))
                {
                        values[i] = toast_flatten_tuple_attribute(values[i],
                                                                                                          att[i]->atttypid,
                                                                                                          att[i]->atttypmod);
                }
        }

        /*
         * Determine total space needed
         */
        len = offsetof(HeapTupleHeaderData, t_bits);

        if (hasnull)
                len += BITMAPLEN(numberOfAttributes);

        if (tupleDescriptor->tdhasoid)
                len += sizeof(Oid);

        hoff = len = MAXALIGN(len); /* align user data safely */

        data_len = ComputeDataSize(tupleDescriptor, values, nulls);

        len += data_len;

        /*
         * Allocate and zero the space needed.  Note that the tuple body and
         * HeapTupleData management structure are allocated in one chunk.
         */
        tuple = (HeapTuple) palloc0(HEAPTUPLESIZE + len);
        tuple->t_data = td = (HeapTupleHeader) ((char *) tuple + HEAPTUPLESIZE);

        /*
         * And fill in the information.  Note we fill the Datum fields even though
         * this tuple may never become a Datum.
         */
        tuple->t_len = len;
        ItemPointerSetInvalid(&(tuple->t_self));
        tuple->t_tableOid = InvalidOid;

        HeapTupleHeaderSetDatumLength(td, len);
        HeapTupleHeaderSetTypeId(td, tupleDescriptor->tdtypeid);
        HeapTupleHeaderSetTypMod(td, tupleDescriptor->tdtypmod);

        HeapTupleHeaderSetNatts(td, numberOfAttributes);
        td->t_hoff = hoff;

        if (tupleDescriptor->tdhasoid)          /* else leave infomask = 0 */
                td->t_infomask = HEAP_HASOID;

        DataFill(tupleDescriptor,
                         values,
                         nulls,
                         (char *) td + hoff,
                         data_len,
                         &td->t_infomask,
                         (hasnull ? td->t_bits : NULL));

        return tuple;
}


/*
 * heap_modify_tuple
 *              form a new tuple from an old tuple and a set of replacement values.
 *
 * The replValues, replIsnull, and doReplace arrays must be of the length
 * indicated by tupleDesc->natts.  The new tuple is constructed using the data
 * from replValues/replIsnull at columns where doReplace is true, and using
 * the data from the old tuple at columns where doReplace is false.
 *
 * The result is allocated in the current memory context.
 */
HeapTuple
heap_modify_tuple(HeapTuple tuple,
                                  TupleDesc tupleDesc,
                                  Datum *replValues,
                                  bool *replIsnull,
                                  bool *doReplace)
{
        int                     numberOfAttributes = tupleDesc->natts;
        int                     attoff;
        Datum      *values;
        bool       *isnull;
        HeapTuple       newTuple;

        /*
         * allocate and fill values and isnull arrays from either the tuple or the
         * repl information, as appropriate.
         *
         * NOTE: it's debatable whether to use heap_deform_tuple() here or just
         * heap_getattr() only the non-replaced colums.  The latter could win if
         * there are many replaced columns and few non-replaced ones. However,
         * heap_deform_tuple costs only O(N) while the heap_getattr way would cost
         * O(N^2) if there are many non-replaced columns, so it seems better to
         * err on the side of linear cost.
         */
        values = (Datum *) palloc(numberOfAttributes * sizeof(Datum));
        isnull = (bool *) palloc(numberOfAttributes * sizeof(bool));

        heap_deform_tuple(tuple, tupleDesc, values, isnull);

        for (attoff = 0; attoff < numberOfAttributes; attoff++)
        {
                if (doReplace[attoff])
                {
                        values[attoff] = replValues[attoff];
                        isnull[attoff] = replIsnull[attoff];
                }
        }

        /*
         * create a new tuple from the values and isnull arrays
         */
        newTuple = heap_form_tuple(tupleDesc, values, isnull);

        pfree(values);
        pfree(isnull);

        /*
         * copy the identification info of the old tuple: t_ctid, t_self, and OID
         * (if any)
         */
        newTuple->t_data->t_ctid = tuple->t_data->t_ctid;
        newTuple->t_self = tuple->t_self;
        newTuple->t_tableOid = tuple->t_tableOid;
        if (tupleDesc->tdhasoid)
                HeapTupleSetOid(newTuple, HeapTupleGetOid(tuple));

        return newTuple;
}

/* ----------------
 *              heap_modifytuple
 *
 *              forms a new tuple from an old tuple and a set of replacement values.
 *              returns a new palloc'ed tuple.
 *
 * OLD API with char 'n'/' ' convention for indicating nulls, and
 * char 'r'/' ' convention for indicating whether to replace columns.
 * ----------------
 */
HeapTuple
heap_modifytuple(HeapTuple tuple,
                                 TupleDesc tupleDesc,
                                 Datum *replValues,
                                 char *replNulls,
                                 char *replActions)
{
        int                     numberOfAttributes = tupleDesc->natts;
        int                     attoff;
        Datum      *values;
        char       *nulls;
        HeapTuple       newTuple;

        /*
         * allocate and fill values and nulls arrays from either the tuple or the
         * repl information, as appropriate.
         *
         * NOTE: it's debatable whether to use heap_deformtuple() here or just
         * heap_getattr() only the non-replaced colums.  The latter could win if
         * there are many replaced columns and few non-replaced ones. However,
         * heap_deformtuple costs only O(N) while the heap_getattr way would cost
         * O(N^2) if there are many non-replaced columns, so it seems better to
         * err on the side of linear cost.
         */
        values = (Datum *) palloc(numberOfAttributes * sizeof(Datum));
        nulls = (char *) palloc(numberOfAttributes * sizeof(char));

        heap_deformtuple(tuple, tupleDesc, values, nulls);

        for (attoff = 0; attoff < numberOfAttributes; attoff++)
        {
                if (replActions[attoff] == 'r')
                {
                        values[attoff] = replValues[attoff];
                        nulls[attoff] = replNulls[attoff];
                }
                else if (replActions[attoff] != ' ')
                        elog(ERROR, "unrecognized replace flag: %d",
                                 (int) replActions[attoff]);
        }

        /*
         * create a new tuple from the values and nulls arrays
         */
        newTuple = heap_formtuple(tupleDesc, values, nulls);

        pfree(values);
        pfree(nulls);

        /*
         * copy the identification info of the old tuple: t_ctid, t_self, and OID
         * (if any)
         */
        newTuple->t_data->t_ctid = tuple->t_data->t_ctid;
        newTuple->t_self = tuple->t_self;
        newTuple->t_tableOid = tuple->t_tableOid;
        if (tupleDesc->tdhasoid)
                HeapTupleSetOid(newTuple, HeapTupleGetOid(tuple));

        return newTuple;
}

/*
 * heap_deform_tuple
 *              Given a tuple, extract data into values/isnull arrays; this is
 *              the inverse of heap_form_tuple.
 *
 *              Storage for the values/isnull arrays is provided by the caller;
 *              it should be sized according to tupleDesc->natts not tuple->t_natts.
 *
 *              Note that for pass-by-reference datatypes, the pointer placed
 *              in the Datum will point into the given tuple.
 *
 *              When all or most of a tuple's fields need to be extracted,
 *              this routine will be significantly quicker than a loop around
 *              heap_getattr; the loop will become O(N^2) as soon as any
 *              noncacheable attribute offsets are involved.
 */
void
heap_deform_tuple(HeapTuple tuple, TupleDesc tupleDesc,
                                  Datum *values, bool *isnull)
{
        HeapTupleHeader tup = tuple->t_data;
        bool            hasnulls = HeapTupleHasNulls(tuple);
        Form_pg_attribute *att = tupleDesc->attrs;
        int                     tdesc_natts = tupleDesc->natts;
        int                     natts;                  /* number of atts to extract */
        int                     attnum;
        char       *tp;                         /* ptr to tuple data */
        long            off;                    /* offset in tuple data */
        bits8      *bp = tup->t_bits;           /* ptr to null bitmap in tuple */
        bool            slow = false;   /* can we use/set attcacheoff? */

        natts = HeapTupleHeaderGetNatts(tup);

        /*
         * In inheritance situations, it is possible that the given tuple actually
         * has more fields than the caller is expecting.  Don't run off the end of
         * the caller's arrays.
         */
        natts = Min(natts, tdesc_natts);

        tp = (char *) tup + tup->t_hoff;

        off = 0;

        for (attnum = 0; attnum < natts; attnum++)
        {
                Form_pg_attribute thisatt = att[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 */
        }

        /*
         * If tuple doesn't have all the atts indicated by tupleDesc, read the
         * rest as null
         */
        for (; attnum < tdesc_natts; attnum++)
        {
                values[attnum] = (Datum) 0;
                isnull[attnum] = true;
        }
}

/* ----------------
 *              heap_deformtuple
 *
 *              Given a tuple, extract data into values/nulls arrays; this is
 *              the inverse of heap_formtuple.
 *
 *              Storage for the values/nulls arrays is provided by the caller;
 *              it should be sized according to tupleDesc->natts not tuple->t_natts.
 *
 *              Note that for pass-by-reference datatypes, the pointer placed
 *              in the Datum will point into the given tuple.
 *
 *              When all or most of a tuple's fields need to be extracted,
 *              this routine will be significantly quicker than a loop around
 *              heap_getattr; the loop will become O(N^2) as soon as any
 *              noncacheable attribute offsets are involved.
 *
 * OLD API with char 'n'/' ' convention for indicating nulls
 * ----------------
 */
void
heap_deformtuple(HeapTuple tuple,
                                 TupleDesc tupleDesc,
                                 Datum *values,
                                 char *nulls)
{
        HeapTupleHeader tup = tuple->t_data;
        bool            hasnulls = HeapTupleHasNulls(tuple);
        Form_pg_attribute *att = tupleDesc->attrs;
        int                     tdesc_natts = tupleDesc->natts;
        int                     natts;                  /* number of atts to extract */
        int                     attnum;
        char       *tp;                         /* ptr to tuple data */
        long            off;                    /* offset in tuple data */
        bits8      *bp = tup->t_bits;           /* ptr to null bitmap in tuple */
        bool            slow = false;   /* can we use/set attcacheoff? */

        natts = HeapTupleHeaderGetNatts(tup);

        /*
         * In inheritance situations, it is possible that the given tuple actually
         * has more fields than the caller is expecting.  Don't run off the end of
         * the caller's arrays.
         */
        natts = Min(natts, tdesc_natts);

        tp = (char *) tup + tup->t_hoff;

        off = 0;

        for (attnum = 0; attnum < natts; attnum++)
        {
                Form_pg_attribute thisatt = att[attnum];

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

                nulls[attnum] = ' ';

                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 */
        }

        /*
         * If tuple doesn't have all the atts indicated by tupleDesc, read the
         * rest as null
         */
        for (; attnum < tdesc_natts; attnum++)
        {
                values[attnum] = (Datum) 0;
                nulls[attnum] = 'n';
        }
}

/*
 * slot_deform_tuple
 *              Given a TupleTableSlot, extract data from the slot's physical tuple
 *              into its Datum/isnull arrays.  Data is extracted up through the
 *              natts'th column (caller must ensure this is a legal column number).
 *
 *              This is essentially an incremental version of heap_deform_tuple:
 *              on each call we extract attributes up to the one needed, without
 *              re-computing information about previously extracted attributes.
 *              slot->tts_nvalid is the number of attributes already extracted.
 */
static void
slot_deform_tuple(TupleTableSlot *slot, int natts)
{
        HeapTuple       tuple = slot->tts_tuple;
        TupleDesc       tupleDesc = slot->tts_tupleDescriptor;
        Datum      *values = slot->tts_values;
        bool       *isnull = slot->tts_isnull;
        HeapTupleHeader tup = tuple->t_data;
        bool            hasnulls = HeapTupleHasNulls(tuple);
        Form_pg_attribute *att = tupleDesc->attrs;
        int                     attnum;
        char       *tp;                         /* ptr to tuple data */
        long            off;                    /* offset in tuple data */
        bits8      *bp = tup->t_bits;           /* ptr to null bitmap in tuple */
        bool            slow;                   /* can we use/set attcacheoff? */

        /*
         * Check whether the first call for this tuple, and initialize or restore
         * loop state.
         */
        attnum = slot->tts_nvalid;
        if (attnum == 0)
        {
                /* Start from the first attribute */
                off = 0;
                slow = false;
        }
        else
        {
                /* Restore state from previous execution */
                off = slot->tts_off;
                slow = slot->tts_slow;
        }

        tp = (char *) tup + tup->t_hoff;

        for (; attnum < natts; attnum++)
        {
                Form_pg_attribute thisatt = att[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 */
        }

        /*
         * Save state for next execution
         */
        slot->tts_nvalid = attnum;
        slot->tts_off = off;
        slot->tts_slow = slow;
}

/*
 * slot_getattr
 *              This function fetches an attribute of the slot's current tuple.
 *              It is functionally equivalent to heap_getattr, but fetches of
 *              multiple attributes of the same tuple will be optimized better,
 *              because we avoid O(N^2) behavior from multiple calls of
 *              nocachegetattr(), even when attcacheoff isn't usable.
 *
 *              A difference from raw heap_getattr is that attnums beyond the
 *              slot's tupdesc's last attribute will be considered NULL even
 *              when the physical tuple is longer than the tupdesc.
 */
Datum
slot_getattr(TupleTableSlot *slot, int attnum, bool *isnull)
{
        HeapTuple       tuple = slot->tts_tuple;
        TupleDesc       tupleDesc = slot->tts_tupleDescriptor;
        HeapTupleHeader tup;

        /*
         * system attributes are handled by heap_getsysattr
         */
        if (attnum <= 0)
        {
                if (tuple == NULL)              /* internal error */
                        elog(ERROR, "cannot extract system attribute from virtual tuple");
                if (slot->tts_mintuple) /* internal error */
                        elog(ERROR, "cannot extract system attribute from minimal tuple");
                return heap_getsysattr(tuple, attnum, tupleDesc, isnull);
        }

        /*
         * fast path if desired attribute already cached
         */
        if (attnum <= slot->tts_nvalid)
        {
                *isnull = slot->tts_isnull[attnum - 1];
                return slot->tts_values[attnum - 1];
        }

        /*
         * return NULL if attnum is out of range according to the tupdesc
         */
        if (attnum > tupleDesc->natts)
        {
                *isnull = true;
                return (Datum) 0;
        }

        /*
         * otherwise we had better have a physical tuple (tts_nvalid should equal
         * natts in all virtual-tuple cases)
         */
        if (tuple == NULL)                      /* internal error */
                elog(ERROR, "cannot extract attribute from empty tuple slot");

        /*
         * return NULL if attnum is out of range according to the tuple
         *
         * (We have to check this separately because of various inheritance and
         * table-alteration scenarios: the tuple could be either longer or shorter
         * than the tupdesc.)
         */
        tup = tuple->t_data;
        if (attnum > HeapTupleHeaderGetNatts(tup))
        {
                *isnull = true;
                return (Datum) 0;
        }

        /*
         * check if target attribute is null: no point in groveling through tuple
         */
        if (HeapTupleHasNulls(tuple) && att_isnull(attnum - 1, tup->t_bits))
        {
                *isnull = true;
                return (Datum) 0;
        }

        /*
         * If the attribute's column has been dropped, we force a NULL result.
         * This case should not happen in normal use, but it could happen if we
         * are executing a plan cached before the column was dropped.
         */
        if (tupleDesc->attrs[attnum - 1]->attisdropped)
        {
                *isnull = true;
                return (Datum) 0;
        }

        /*
         * Extract the attribute, along with any preceding attributes.
         */
        slot_deform_tuple(slot, attnum);

        /*
         * The result is acquired from tts_values array.
         */
        *isnull = slot->tts_isnull[attnum - 1];
        return slot->tts_values[attnum - 1];
}

/*
 * slot_getallattrs
 *              This function forces all the entries of the slot's Datum/isnull
 *              arrays to be valid.  The caller may then extract data directly
 *              from those arrays instead of using slot_getattr.
 */
void
slot_getallattrs(TupleTableSlot *slot)
{
        int                     tdesc_natts = slot->tts_tupleDescriptor->natts;
        int                     attnum;
        HeapTuple       tuple;

        /* Quick out if we have 'em all already */
        if (slot->tts_nvalid == tdesc_natts)
                return;

        /*
         * otherwise we had better have a physical tuple (tts_nvalid should equal
         * natts in all virtual-tuple cases)
         */
        tuple = slot->tts_tuple;
        if (tuple == NULL)                      /* internal error */
                elog(ERROR, "cannot extract attribute from empty tuple slot");

        /*
         * load up any slots available from physical tuple
         */
        attnum = HeapTupleHeaderGetNatts(tuple->t_data);
        attnum = Min(attnum, tdesc_natts);

        slot_deform_tuple(slot, attnum);

        /*
         * If tuple doesn't have all the atts indicated by tupleDesc, read the
         * rest as null
         */
        for (; attnum < tdesc_natts; attnum++)
        {
                slot->tts_values[attnum] = (Datum) 0;
                slot->tts_isnull[attnum] = true;
        }
        slot->tts_nvalid = tdesc_natts;
}

/*
 * slot_getsomeattrs
 *              This function forces the entries of the slot's Datum/isnull
 *              arrays to be valid at least up through the attnum'th entry.
 */
void
slot_getsomeattrs(TupleTableSlot *slot, int attnum)
{
        HeapTuple       tuple;
        int                     attno;

        /* Quick out if we have 'em all already */
        if (slot->tts_nvalid >= attnum)
                return;

        /* Check for caller error */
        if (attnum <= 0 || attnum > slot->tts_tupleDescriptor->natts)
                elog(ERROR, "invalid attribute number %d", attnum);

        /*
         * otherwise we had better have a physical tuple (tts_nvalid should equal
         * natts in all virtual-tuple cases)
         */
        tuple = slot->tts_tuple;
        if (tuple == NULL)                      /* internal error */
                elog(ERROR, "cannot extract attribute from empty tuple slot");

        /*
         * load up any slots available from physical tuple
         */
        attno = HeapTupleHeaderGetNatts(tuple->t_data);
        attno = Min(attno, attnum);

        slot_deform_tuple(slot, attno);

        /*
         * If tuple doesn't have all the atts indicated by tupleDesc, read the
         * rest as null
         */
        for (; attno < attnum; attno++)
        {
                slot->tts_values[attno] = (Datum) 0;
                slot->tts_isnull[attno] = true;
        }
        slot->tts_nvalid = attnum;
}

/*
 * slot_attisnull
 *              Detect whether an attribute of the slot is null, without
 *              actually fetching it.
 */
bool
slot_attisnull(TupleTableSlot *slot, int attnum)
{
        HeapTuple       tuple = slot->tts_tuple;
        TupleDesc       tupleDesc = slot->tts_tupleDescriptor;

        /*
         * system attributes are handled by heap_attisnull
         */
        if (attnum <= 0)
        {
                if (tuple == NULL)              /* internal error */
                        elog(ERROR, "cannot extract system attribute from virtual tuple");
                if (slot->tts_mintuple) /* internal error */
                        elog(ERROR, "cannot extract system attribute from minimal tuple");
                return heap_attisnull(tuple, attnum);
        }

        /*
         * fast path if desired attribute already cached
         */
        if (attnum <= slot->tts_nvalid)
                return slot->tts_isnull[attnum - 1];

        /*
         * return NULL if attnum is out of range according to the tupdesc
         */
        if (attnum > tupleDesc->natts)
                return true;

        /*
         * otherwise we had better have a physical tuple (tts_nvalid should equal
         * natts in all virtual-tuple cases)
         */
        if (tuple == NULL)                      /* internal error */
                elog(ERROR, "cannot extract attribute from empty tuple slot");

        /* and let the tuple tell it */
        return heap_attisnull(tuple, attnum);
}

/*
 * heap_freetuple
 */
void
heap_freetuple(HeapTuple htup)
{
        pfree(htup);
}


/*
 * heap_form_minimal_tuple
 *              construct a MinimalTuple from the given values[] and isnull[] arrays,
 *              which are of the length indicated by tupleDescriptor->natts
 *
 * This is exactly like heap_form_tuple() except that the result is a
 * "minimal" tuple lacking a HeapTupleData header as well as room for system
 * columns.
 *
 * The result is allocated in the current memory context.
 */
MinimalTuple
heap_form_minimal_tuple(TupleDesc tupleDescriptor,
                                                Datum *values,
                                                bool *isnull)
{
        MinimalTuple tuple;                     /* return tuple */
        Size            len,
                                data_len;
        int                     hoff;
        bool            hasnull = false;
        Form_pg_attribute *att = tupleDescriptor->attrs;
        int                     numberOfAttributes = tupleDescriptor->natts;
        int                     i;

        if (numberOfAttributes > MaxTupleAttributeNumber)
                ereport(ERROR,
                                (errcode(ERRCODE_TOO_MANY_COLUMNS),
                                 errmsg("number of columns (%d) exceeds limit (%d)",
                                                numberOfAttributes, MaxTupleAttributeNumber)));

        /*
         * Check for nulls and embedded tuples; expand any toasted attributes in
         * embedded tuples.  This preserves the invariant that toasting can only
         * go one level deep.
         *
         * We can skip calling toast_flatten_tuple_attribute() if the attribute
         * couldn't possibly be of composite type.  All composite datums are
         * varlena and have alignment 'd'; furthermore they aren't arrays. Also,
         * if an attribute is already toasted, it must have been sent to disk
         * already and so cannot contain toasted attributes.
         */
        for (i = 0; i < numberOfAttributes; i++)
        {
                if (isnull[i])
                        hasnull = true;
                else if (att[i]->attlen == -1 &&
                                 att[i]->attalign == 'd' &&
                                 att[i]->attndims == 0 &&
                                 !VARATT_IS_EXTENDED(values[i]))
                {
                        values[i] = toast_flatten_tuple_attribute(values[i],
                                                                                                          att[i]->atttypid,
                                                                                                          att[i]->atttypmod);
                }
        }

        /*
         * Determine total space needed
         */
        len = offsetof(MinimalTupleData, t_bits);

        if (hasnull)
                len += BITMAPLEN(numberOfAttributes);

        if (tupleDescriptor->tdhasoid)
                len += sizeof(Oid);

        hoff = len = MAXALIGN(len); /* align user data safely */

        data_len = heap_compute_data_size(tupleDescriptor, values, isnull);

        len += data_len;

        /*
         * Allocate and zero the space needed.
         */
        tuple = (MinimalTuple) palloc0(len);

        /*
         * And fill in the information.
         */
        tuple->t_len = len;
        HeapTupleHeaderSetNatts(tuple, numberOfAttributes);
        tuple->t_hoff = hoff + MINIMAL_TUPLE_OFFSET;

        if (tupleDescriptor->tdhasoid)          /* else leave infomask = 0 */
                tuple->t_infomask = HEAP_HASOID;

        heap_fill_tuple(tupleDescriptor,
                                        values,
                                        isnull,
                                        (char *) tuple + hoff,
                                        data_len,
                                        &tuple->t_infomask,
                                        (hasnull ? tuple->t_bits : NULL));

        return tuple;
}

/*
 * heap_free_minimal_tuple
 */
void
heap_free_minimal_tuple(MinimalTuple mtup)
{
        pfree(mtup);
}

/*
 * heap_copy_minimal_tuple
 *              copy a MinimalTuple
 *
 * The result is allocated in the current memory context.
 */
MinimalTuple
heap_copy_minimal_tuple(MinimalTuple mtup)
{
        MinimalTuple result;

        result = (MinimalTuple) palloc(mtup->t_len);
        memcpy(result, mtup, mtup->t_len);
        return result;
}

/*
 * heap_tuple_from_minimal_tuple
 *              create a HeapTuple by copying from a MinimalTuple;
 *              system columns are filled with zeroes
 *
 * The result is allocated in the current memory context.
 * The HeapTuple struct, tuple header, and tuple data are all allocated
 * as a single palloc() block.
 */
HeapTuple
heap_tuple_from_minimal_tuple(MinimalTuple mtup)
{
        HeapTuple       result;
        uint32          len = mtup->t_len + MINIMAL_TUPLE_OFFSET;

        result = (HeapTuple) palloc(HEAPTUPLESIZE + len);
        result->t_len = len;
        ItemPointerSetInvalid(&(result->t_self));
        result->t_tableOid = InvalidOid;
        result->t_data = (HeapTupleHeader) ((char *) result + HEAPTUPLESIZE);
        memcpy((char *) result->t_data + MINIMAL_TUPLE_OFFSET, mtup, mtup->t_len);
        memset(result->t_data, 0, offsetof(HeapTupleHeaderData, t_infomask2));
        return result;
}

/*
 * minimal_tuple_from_heap_tuple
 *              create a MinimalTuple by copying from a HeapTuple
 *
 * The result is allocated in the current memory context.
 */
MinimalTuple
minimal_tuple_from_heap_tuple(HeapTuple htup)
{
        MinimalTuple result;
        uint32          len;

        Assert(htup->t_len > MINIMAL_TUPLE_OFFSET);
        len = htup->t_len - MINIMAL_TUPLE_OFFSET;
        result = (MinimalTuple) palloc(len);
        memcpy(result, (char *) htup->t_data + MINIMAL_TUPLE_OFFSET, len);
        result->t_len = len;
        return result;
}


/* ----------------
 *              heap_addheader
 *
 * This routine forms a HeapTuple by copying the given structure (tuple
 * data) and adding a generic header.  Note that the tuple data is
 * presumed to contain no null fields and no varlena fields.
 *
 * This routine is really only useful for certain system tables that are
 * known to be fixed-width and null-free.  Currently it is only used for
 * pg_attribute tuples.
 * ----------------
 */
HeapTuple
heap_addheader(int natts,               /* max domain index */
                           bool withoid,        /* reserve space for oid */
                           Size structlen,      /* its length */
                           void *structure) /* pointer to the struct */
{
        HeapTuple       tuple;
        HeapTupleHeader td;
        Size            len;
        int                     hoff;

        AssertArg(natts > 0);

        /* header needs no null bitmap */
        hoff = offsetof(HeapTupleHeaderData, t_bits);
        if (withoid)
                hoff += sizeof(Oid);
        hoff = MAXALIGN(hoff);
        len = hoff + structlen;

        tuple = (HeapTuple) palloc0(HEAPTUPLESIZE + len);
        tuple->t_data = td = (HeapTupleHeader) ((char *) tuple + HEAPTUPLESIZE);

        tuple->t_len = len;
        ItemPointerSetInvalid(&(tuple->t_self));
        tuple->t_tableOid = InvalidOid;

        /* we don't bother to fill the Datum fields */

        HeapTupleHeaderSetNatts(td, natts);
        td->t_hoff = hoff;

        if (withoid)                            /* else leave infomask = 0 */
                td->t_infomask = HEAP_HASOID;

        memcpy((char *) td + hoff, structure, structlen);

        return tuple;
}