execTuples.c

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/*-------------------------------------------------------------------------
 *
 * execTuples.c
 *    Routines dealing with TupleTableSlots.  These are used for resource
 *    management associated with tuples (eg, releasing buffer pins for
 *    tuples in disk buffers, or freeing the memory occupied by transient
 *    tuples).  Slots also provide access abstraction that lets us implement
 *    "virtual" tuples to reduce data-copying overhead.
 *
 *    Routines dealing with the type information for tuples. Currently,
 *    the type information for a tuple is an array of FormData_pg_attribute.
 *    This information is needed by routines manipulating tuples
 *    (getattribute, formtuple, etc.).
 *
 *
 *   EXAMPLE OF HOW TABLE ROUTINES WORK
 *      Suppose we have a query such as SELECT emp.name FROM emp and we have
 *      a single SeqScan node in the query plan.
 *
 *      At ExecutorStart()
 *      ----------------
 *
 *      - ExecInitSeqScan() calls ExecInitScanTupleSlot() to construct a
 *        TupleTableSlots for the tuples returned by the access method, and
 *        ExecInitResultTypeTL() to define the node's return
 *        type. ExecAssignScanProjectionInfo() will, if necessary, create
 *        another TupleTableSlot for the tuples resulting from performing
 *        target list projections.
 *
 *      During ExecutorRun()
 *      ----------------
 *      - SeqNext() calls ExecStoreBufferHeapTuple() to place the tuple
 *        returned by the access method into the scan tuple slot.
 *
 *      - ExecSeqScan() (via ExecScan), if necessary, calls ExecProject(),
 *        putting the result of the projection in the result tuple slot. If
 *        not necessary, it directly returns the slot returned by SeqNext().
 *
 *      - ExecutePlan() calls the output function.
 *
 *      The important thing to watch in the executor code is how pointers
 *      to the slots containing tuples are passed instead of the tuples
 *      themselves.  This facilitates the communication of related information
 *      (such as whether or not a tuple should be pfreed, what buffer contains
 *      this tuple, the tuple's tuple descriptor, etc).  It also allows us
 *      to avoid physically constructing projection tuples in many cases.
 *
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/execTuples.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/heaptoast.h"
#include "access/htup_details.h"
#include "access/tupdesc_details.h"
#include "catalog/pg_type.h"
#include "funcapi.h"
#include "nodes/nodeFuncs.h"
#include "storage/bufmgr.h"
#include "utils/builtins.h"
#include "utils/expandeddatum.h"
#include "utils/lsyscache.h"
#include "utils/typcache.h"

static TupleDesc ExecTypeFromTLInternal(List *targetList,
                                        bool skipjunk);
static pg_attribute_always_inline void slot_deform_heap_tuple(TupleTableSlot *slot, HeapTuple tuple, uint32 *offp,
                                                              int natts);
static inline void tts_buffer_heap_store_tuple(TupleTableSlot *slot,
                                               HeapTuple tuple,
                                               Buffer buffer,
                                               bool transfer_pin);
static void tts_heap_store_tuple(TupleTableSlot *slot, HeapTuple tuple, bool shouldFree);


const TupleTableSlotOps TTSOpsVirtual;
const TupleTableSlotOps TTSOpsHeapTuple;
const TupleTableSlotOps TTSOpsMinimalTuple;
const TupleTableSlotOps TTSOpsBufferHeapTuple;


/*
 * TupleTableSlotOps implementations.
 */

/*
 * TupleTableSlotOps implementation for VirtualTupleTableSlot.
 */
static void
tts_virtual_init(TupleTableSlot *slot)
{
}

static void
tts_virtual_release(TupleTableSlot *slot)
{
}

static void
tts_virtual_clear(TupleTableSlot *slot)
{
    if (unlikely(TTS_SHOULDFREE(slot)))
    {
        VirtualTupleTableSlot *vslot = (VirtualTupleTableSlot *) slot;

        pfree(vslot->data);
        vslot->data = NULL;

        slot->tts_flags &= ~TTS_FLAG_SHOULDFREE;
    }

    slot->tts_nvalid = 0;
    slot->tts_flags |= TTS_FLAG_EMPTY;
    ItemPointerSetInvalid(&slot->tts_tid);
}

/*
 * VirtualTupleTableSlots always have fully populated tts_values and
 * tts_isnull arrays.  So this function should never be called.
 */
static void
tts_virtual_getsomeattrs(TupleTableSlot *slot, int natts)
{
    elog(ERROR, "getsomeattrs is not required to be called on a virtual tuple table slot");
}

/*
 * VirtualTupleTableSlots never provide system attributes (except those
 * handled generically, such as tableoid).  We generally shouldn't get
 * here, but provide a user-friendly message if we do.
 */
static Datum
tts_virtual_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
{
    Assert(!TTS_EMPTY(slot));

    ereport(ERROR,
            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
             errmsg("cannot retrieve a system column in this context")));

    return 0;                   /* silence compiler warnings */
}

/*
 * To materialize a virtual slot all the datums that aren't passed by value
 * have to be copied into the slot's memory context.  To do so, compute the
 * required size, and allocate enough memory to store all attributes.  That's
 * good for cache hit ratio, but more importantly requires only memory
 * allocation/deallocation.
 */
static void
tts_virtual_materialize(TupleTableSlot *slot)
{
    VirtualTupleTableSlot *vslot = (VirtualTupleTableSlot *) slot;
    TupleDesc   desc = slot->tts_tupleDescriptor;
    Size        sz = 0;
    char       *data;

    /* already materialized */
    if (TTS_SHOULDFREE(slot))
        return;

    /* compute size of memory required */
    for (int natt = 0; natt < desc->natts; natt++)
    {
        Form_pg_attribute att = TupleDescAttr(desc, natt);
        Datum       val;

        if (att->attbyval || slot->tts_isnull[natt])
            continue;

        val = slot->tts_values[natt];

        if (att->attlen == -1 &&
            VARATT_IS_EXTERNAL_EXPANDED(DatumGetPointer(val)))
        {
            /*
             * We want to flatten the expanded value so that the materialized
             * slot doesn't depend on it.
             */
            sz = att_align_nominal(sz, att->attalign);
            sz += EOH_get_flat_size(DatumGetEOHP(val));
        }
        else
        {
            sz = att_align_nominal(sz, att->attalign);
            sz = att_addlength_datum(sz, att->attlen, val);
        }
    }

    /* all data is byval */
    if (sz == 0)
        return;

    /* allocate memory */
    vslot->data = data = MemoryContextAlloc(slot->tts_mcxt, sz);
    slot->tts_flags |= TTS_FLAG_SHOULDFREE;

    /* and copy all attributes into the pre-allocated space */
    for (int natt = 0; natt < desc->natts; natt++)
    {
        Form_pg_attribute att = TupleDescAttr(desc, natt);
        Datum       val;

        if (att->attbyval || slot->tts_isnull[natt])
            continue;

        val = slot->tts_values[natt];

        if (att->attlen == -1 &&
            VARATT_IS_EXTERNAL_EXPANDED(DatumGetPointer(val)))
        {
            Size        data_length;

            /*
             * We want to flatten the expanded value so that the materialized
             * slot doesn't depend on it.
             */
            ExpandedObjectHeader *eoh = DatumGetEOHP(val);

            data = (char *) att_align_nominal(data,
                                              att->attalign);
            data_length = EOH_get_flat_size(eoh);
            EOH_flatten_into(eoh, data, data_length);

            slot->tts_values[natt] = PointerGetDatum(data);
            data += data_length;
        }
        else
        {
            Size        data_length = 0;

            data = (char *) att_align_nominal(data, att->attalign);
            data_length = att_addlength_datum(data_length, att->attlen, val);

            memcpy(data, DatumGetPointer(val), data_length);

            slot->tts_values[natt] = PointerGetDatum(data);
            data += data_length;
        }
    }
}

static void
tts_virtual_copyslot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
{
    TupleDesc   srcdesc = srcslot->tts_tupleDescriptor;

    Assert(srcdesc->natts <= dstslot->tts_tupleDescriptor->natts);

    tts_virtual_clear(dstslot);

    slot_getallattrs(srcslot);

    for (int natt = 0; natt < srcdesc->natts; natt++)
    {
        dstslot->tts_values[natt] = srcslot->tts_values[natt];
        dstslot->tts_isnull[natt] = srcslot->tts_isnull[natt];
    }

    dstslot->tts_nvalid = srcdesc->natts;
    dstslot->tts_flags &= ~TTS_FLAG_EMPTY;

    /* make sure storage doesn't depend on external memory */
    tts_virtual_materialize(dstslot);
}

static HeapTuple
tts_virtual_copy_heap_tuple(TupleTableSlot *slot)
{
    Assert(!TTS_EMPTY(slot));

    return heap_form_tuple(slot->tts_tupleDescriptor,
                           slot->tts_values,
                           slot->tts_isnull);
}

static MinimalTuple
tts_virtual_copy_minimal_tuple(TupleTableSlot *slot)
{
    Assert(!TTS_EMPTY(slot));

    return heap_form_minimal_tuple(slot->tts_tupleDescriptor,
                                   slot->tts_values,
                                   slot->tts_isnull);
}


/*
 * TupleTableSlotOps implementation for HeapTupleTableSlot.
 */

static void
tts_heap_init(TupleTableSlot *slot)
{
}

static void
tts_heap_release(TupleTableSlot *slot)
{
}

static void
tts_heap_clear(TupleTableSlot *slot)
{
    HeapTupleTableSlot *hslot = (HeapTupleTableSlot *) slot;

    /* Free the memory for the heap tuple if it's allowed. */
    if (TTS_SHOULDFREE(slot))
    {
        heap_freetuple(hslot->tuple);
        slot->tts_flags &= ~TTS_FLAG_SHOULDFREE;
    }

    slot->tts_nvalid = 0;
    slot->tts_flags |= TTS_FLAG_EMPTY;
    ItemPointerSetInvalid(&slot->tts_tid);
    hslot->off = 0;
    hslot->tuple = NULL;
}

static void
tts_heap_getsomeattrs(TupleTableSlot *slot, int natts)
{
    HeapTupleTableSlot *hslot = (HeapTupleTableSlot *) slot;

    Assert(!TTS_EMPTY(slot));

    slot_deform_heap_tuple(slot, hslot->tuple, &hslot->off, natts);
}

static Datum
tts_heap_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
{
    HeapTupleTableSlot *hslot = (HeapTupleTableSlot *) slot;

    Assert(!TTS_EMPTY(slot));

    /*
     * In some code paths it's possible to get here with a non-materialized
     * slot, in which case we can't retrieve system columns.
     */
    if (!hslot->tuple)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot retrieve a system column in this context")));

    return heap_getsysattr(hslot->tuple, attnum,
                           slot->tts_tupleDescriptor, isnull);
}

static void
tts_heap_materialize(TupleTableSlot *slot)
{
    HeapTupleTableSlot *hslot = (HeapTupleTableSlot *) slot;
    MemoryContext oldContext;

    Assert(!TTS_EMPTY(slot));

    /* If slot has its tuple already materialized, nothing to do. */
    if (TTS_SHOULDFREE(slot))
        return;

    oldContext = MemoryContextSwitchTo(slot->tts_mcxt);

    /*
     * Have to deform from scratch, otherwise tts_values[] entries could point
     * into the non-materialized tuple (which might be gone when accessed).
     */
    slot->tts_nvalid = 0;
    hslot->off = 0;

    if (!hslot->tuple)
        hslot->tuple = heap_form_tuple(slot->tts_tupleDescriptor,
                                       slot->tts_values,
                                       slot->tts_isnull);
    else
    {
        /*
         * The tuple contained in this slot is not allocated in the memory
         * context of the given slot (else it would have TTS_SHOULDFREE set).
         * Copy the tuple into the given slot's memory context.
         */
        hslot->tuple = heap_copytuple(hslot->tuple);
    }

    slot->tts_flags |= TTS_FLAG_SHOULDFREE;

    MemoryContextSwitchTo(oldContext);
}

static void
tts_heap_copyslot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
{
    HeapTuple   tuple;
    MemoryContext oldcontext;

    oldcontext = MemoryContextSwitchTo(dstslot->tts_mcxt);
    tuple = ExecCopySlotHeapTuple(srcslot);
    MemoryContextSwitchTo(oldcontext);

    ExecStoreHeapTuple(tuple, dstslot, true);
}

static HeapTuple
tts_heap_get_heap_tuple(TupleTableSlot *slot)
{
    HeapTupleTableSlot *hslot = (HeapTupleTableSlot *) slot;

    Assert(!TTS_EMPTY(slot));
    if (!hslot->tuple)
        tts_heap_materialize(slot);

    return hslot->tuple;
}

static HeapTuple
tts_heap_copy_heap_tuple(TupleTableSlot *slot)
{
    HeapTupleTableSlot *hslot = (HeapTupleTableSlot *) slot;

    Assert(!TTS_EMPTY(slot));
    if (!hslot->tuple)
        tts_heap_materialize(slot);

    return heap_copytuple(hslot->tuple);
}

static MinimalTuple
tts_heap_copy_minimal_tuple(TupleTableSlot *slot)
{
    HeapTupleTableSlot *hslot = (HeapTupleTableSlot *) slot;

    if (!hslot->tuple)
        tts_heap_materialize(slot);

    return minimal_tuple_from_heap_tuple(hslot->tuple);
}

static void
tts_heap_store_tuple(TupleTableSlot *slot, HeapTuple tuple, bool shouldFree)
{
    HeapTupleTableSlot *hslot = (HeapTupleTableSlot *) slot;

    tts_heap_clear(slot);

    slot->tts_nvalid = 0;
    hslot->tuple = tuple;
    hslot->off = 0;
    slot->tts_flags &= ~(TTS_FLAG_EMPTY | TTS_FLAG_SHOULDFREE);
    slot->tts_tid = tuple->t_self;

    if (shouldFree)
        slot->tts_flags |= TTS_FLAG_SHOULDFREE;
}


/*
 * TupleTableSlotOps implementation for MinimalTupleTableSlot.
 */

static void
tts_minimal_init(TupleTableSlot *slot)
{
    MinimalTupleTableSlot *mslot = (MinimalTupleTableSlot *) slot;

    /*
     * Initialize the heap tuple pointer to access attributes of the minimal
     * tuple contained in the slot as if its a heap tuple.
     */
    mslot->tuple = &mslot->minhdr;
}

static void
tts_minimal_release(TupleTableSlot *slot)
{
}

static void
tts_minimal_clear(TupleTableSlot *slot)
{
    MinimalTupleTableSlot *mslot = (MinimalTupleTableSlot *) slot;

    if (TTS_SHOULDFREE(slot))
    {
        heap_free_minimal_tuple(mslot->mintuple);
        slot->tts_flags &= ~TTS_FLAG_SHOULDFREE;
    }

    slot->tts_nvalid = 0;
    slot->tts_flags |= TTS_FLAG_EMPTY;
    ItemPointerSetInvalid(&slot->tts_tid);
    mslot->off = 0;
    mslot->mintuple = NULL;
}

static void
tts_minimal_getsomeattrs(TupleTableSlot *slot, int natts)
{
    MinimalTupleTableSlot *mslot = (MinimalTupleTableSlot *) slot;

    Assert(!TTS_EMPTY(slot));

    slot_deform_heap_tuple(slot, mslot->tuple, &mslot->off, natts);
}

static Datum
tts_minimal_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
{
    Assert(!TTS_EMPTY(slot));

    ereport(ERROR,
            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
             errmsg("cannot retrieve a system column in this context")));

    return 0;                   /* silence compiler warnings */
}

static void
tts_minimal_materialize(TupleTableSlot *slot)
{
    MinimalTupleTableSlot *mslot = (MinimalTupleTableSlot *) slot;
    MemoryContext oldContext;

    Assert(!TTS_EMPTY(slot));

    /* If slot has its tuple already materialized, nothing to do. */
    if (TTS_SHOULDFREE(slot))
        return;

    oldContext = MemoryContextSwitchTo(slot->tts_mcxt);

    /*
     * Have to deform from scratch, otherwise tts_values[] entries could point
     * into the non-materialized tuple (which might be gone when accessed).
     */
    slot->tts_nvalid = 0;
    mslot->off = 0;

    if (!mslot->mintuple)
    {
        mslot->mintuple = heap_form_minimal_tuple(slot->tts_tupleDescriptor,
                                                  slot->tts_values,
                                                  slot->tts_isnull);
    }
    else
    {
        /*
         * The minimal tuple contained in this slot is not allocated in the
         * memory context of the given slot (else it would have TTS_SHOULDFREE
         * set).  Copy the minimal tuple into the given slot's memory context.
         */
        mslot->mintuple = heap_copy_minimal_tuple(mslot->mintuple);
    }

    slot->tts_flags |= TTS_FLAG_SHOULDFREE;

    Assert(mslot->tuple == &mslot->minhdr);

    mslot->minhdr.t_len = mslot->mintuple->t_len + MINIMAL_TUPLE_OFFSET;
    mslot->minhdr.t_data = (HeapTupleHeader) ((char *) mslot->mintuple - MINIMAL_TUPLE_OFFSET);

    MemoryContextSwitchTo(oldContext);
}

static void
tts_minimal_copyslot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
{
    MemoryContext oldcontext;
    MinimalTuple mintuple;

    oldcontext = MemoryContextSwitchTo(dstslot->tts_mcxt);
    mintuple = ExecCopySlotMinimalTuple(srcslot);
    MemoryContextSwitchTo(oldcontext);

    ExecStoreMinimalTuple(mintuple, dstslot, true);
}

static MinimalTuple
tts_minimal_get_minimal_tuple(TupleTableSlot *slot)
{
    MinimalTupleTableSlot *mslot = (MinimalTupleTableSlot *) slot;

    if (!mslot->mintuple)
        tts_minimal_materialize(slot);

    return mslot->mintuple;
}

static HeapTuple
tts_minimal_copy_heap_tuple(TupleTableSlot *slot)
{
    MinimalTupleTableSlot *mslot = (MinimalTupleTableSlot *) slot;

    if (!mslot->mintuple)
        tts_minimal_materialize(slot);

    return heap_tuple_from_minimal_tuple(mslot->mintuple);
}

static MinimalTuple
tts_minimal_copy_minimal_tuple(TupleTableSlot *slot)
{
    MinimalTupleTableSlot *mslot = (MinimalTupleTableSlot *) slot;

    if (!mslot->mintuple)
        tts_minimal_materialize(slot);

    return heap_copy_minimal_tuple(mslot->mintuple);
}

static void
tts_minimal_store_tuple(TupleTableSlot *slot, MinimalTuple mtup, bool shouldFree)
{
    MinimalTupleTableSlot *mslot = (MinimalTupleTableSlot *) slot;

    tts_minimal_clear(slot);

    Assert(!TTS_SHOULDFREE(slot));
    Assert(TTS_EMPTY(slot));

    slot->tts_flags &= ~TTS_FLAG_EMPTY;
    slot->tts_nvalid = 0;
    mslot->off = 0;

    mslot->mintuple = mtup;
    Assert(mslot->tuple == &mslot->minhdr);
    mslot->minhdr.t_len = mtup->t_len + MINIMAL_TUPLE_OFFSET;
    mslot->minhdr.t_data = (HeapTupleHeader) ((char *) mtup - MINIMAL_TUPLE_OFFSET);
    /* no need to set t_self or t_tableOid since we won't allow access */

    if (shouldFree)
        slot->tts_flags |= TTS_FLAG_SHOULDFREE;
}


/*
 * TupleTableSlotOps implementation for BufferHeapTupleTableSlot.
 */

static void
tts_buffer_heap_init(TupleTableSlot *slot)
{
}

static void
tts_buffer_heap_release(TupleTableSlot *slot)
{
}

static void
tts_buffer_heap_clear(TupleTableSlot *slot)
{
    BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;

    /*
     * Free the memory for heap tuple if allowed. A tuple coming from buffer
     * can never be freed. But we may have materialized a tuple from buffer.
     * Such a tuple can be freed.
     */
    if (TTS_SHOULDFREE(slot))
    {
        /* We should have unpinned the buffer while materializing the tuple. */
        Assert(!BufferIsValid(bslot->buffer));

        heap_freetuple(bslot->base.tuple);
        slot->tts_flags &= ~TTS_FLAG_SHOULDFREE;
    }

    if (BufferIsValid(bslot->buffer))
        ReleaseBuffer(bslot->buffer);

    slot->tts_nvalid = 0;
    slot->tts_flags |= TTS_FLAG_EMPTY;
    ItemPointerSetInvalid(&slot->tts_tid);
    bslot->base.tuple = NULL;
    bslot->base.off = 0;
    bslot->buffer = InvalidBuffer;
}

static void
tts_buffer_heap_getsomeattrs(TupleTableSlot *slot, int natts)
{
    BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;

    Assert(!TTS_EMPTY(slot));

    slot_deform_heap_tuple(slot, bslot->base.tuple, &bslot->base.off, natts);
}

static Datum
tts_buffer_heap_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
{
    BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;

    Assert(!TTS_EMPTY(slot));

    /*
     * In some code paths it's possible to get here with a non-materialized
     * slot, in which case we can't retrieve system columns.
     */
    if (!bslot->base.tuple)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot retrieve a system column in this context")));

    return heap_getsysattr(bslot->base.tuple, attnum,
                           slot->tts_tupleDescriptor, isnull);
}

static void
tts_buffer_heap_materialize(TupleTableSlot *slot)
{
    BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;
    MemoryContext oldContext;

    Assert(!TTS_EMPTY(slot));

    /* If slot has its tuple already materialized, nothing to do. */
    if (TTS_SHOULDFREE(slot))
        return;

    oldContext = MemoryContextSwitchTo(slot->tts_mcxt);

    /*
     * Have to deform from scratch, otherwise tts_values[] entries could point
     * into the non-materialized tuple (which might be gone when accessed).
     */
    bslot->base.off = 0;
    slot->tts_nvalid = 0;

    if (!bslot->base.tuple)
    {
        /*
         * Normally BufferHeapTupleTableSlot should have a tuple + buffer
         * associated with it, unless it's materialized (which would've
         * returned above). But when it's useful to allow storing virtual
         * tuples in a buffer slot, which then also needs to be
         * materializable.
         */
        bslot->base.tuple = heap_form_tuple(slot->tts_tupleDescriptor,
                                            slot->tts_values,
                                            slot->tts_isnull);
    }
    else
    {
        bslot->base.tuple = heap_copytuple(bslot->base.tuple);

        /*
         * A heap tuple stored in a BufferHeapTupleTableSlot should have a
         * buffer associated with it, unless it's materialized or virtual.
         */
        if (likely(BufferIsValid(bslot->buffer)))
            ReleaseBuffer(bslot->buffer);
        bslot->buffer = InvalidBuffer;
    }

    /*
     * We don't set TTS_FLAG_SHOULDFREE until after releasing the buffer, if
     * any.  This avoids having a transient state that would fall foul of our
     * assertions that a slot with TTS_FLAG_SHOULDFREE doesn't own a buffer.
     * In the unlikely event that ReleaseBuffer() above errors out, we'd
     * effectively leak the copied tuple, but that seems fairly harmless.
     */
    slot->tts_flags |= TTS_FLAG_SHOULDFREE;

    MemoryContextSwitchTo(oldContext);
}

static void
tts_buffer_heap_copyslot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
{
    BufferHeapTupleTableSlot *bsrcslot = (BufferHeapTupleTableSlot *) srcslot;
    BufferHeapTupleTableSlot *bdstslot = (BufferHeapTupleTableSlot *) dstslot;

    /*
     * If the source slot is of a different kind, or is a buffer slot that has
     * been materialized / is virtual, make a new copy of the tuple. Otherwise
     * make a new reference to the in-buffer tuple.
     */
    if (dstslot->tts_ops != srcslot->tts_ops ||
        TTS_SHOULDFREE(srcslot) ||
        !bsrcslot->base.tuple)
    {
        MemoryContext oldContext;

        ExecClearTuple(dstslot);
        dstslot->tts_flags &= ~TTS_FLAG_EMPTY;
        oldContext = MemoryContextSwitchTo(dstslot->tts_mcxt);
        bdstslot->base.tuple = ExecCopySlotHeapTuple(srcslot);
        dstslot->tts_flags |= TTS_FLAG_SHOULDFREE;
        MemoryContextSwitchTo(oldContext);
    }
    else
    {
        Assert(BufferIsValid(bsrcslot->buffer));

        tts_buffer_heap_store_tuple(dstslot, bsrcslot->base.tuple,
                                    bsrcslot->buffer, false);

        /*
         * The HeapTupleData portion of the source tuple might be shorter
         * lived than the destination slot. Therefore copy the HeapTuple into
         * our slot's tupdata, which is guaranteed to live long enough (but
         * will still point into the buffer).
         */
        memcpy(&bdstslot->base.tupdata, bdstslot->base.tuple, sizeof(HeapTupleData));
        bdstslot->base.tuple = &bdstslot->base.tupdata;
    }
}

static HeapTuple
tts_buffer_heap_get_heap_tuple(TupleTableSlot *slot)
{
    BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;

    Assert(!TTS_EMPTY(slot));

    if (!bslot->base.tuple)
        tts_buffer_heap_materialize(slot);

    return bslot->base.tuple;
}

static HeapTuple
tts_buffer_heap_copy_heap_tuple(TupleTableSlot *slot)
{
    BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;

    Assert(!TTS_EMPTY(slot));

    if (!bslot->base.tuple)
        tts_buffer_heap_materialize(slot);

    return heap_copytuple(bslot->base.tuple);
}

static MinimalTuple
tts_buffer_heap_copy_minimal_tuple(TupleTableSlot *slot)
{
    BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;

    Assert(!TTS_EMPTY(slot));

    if (!bslot->base.tuple)
        tts_buffer_heap_materialize(slot);

    return minimal_tuple_from_heap_tuple(bslot->base.tuple);
}

static inline void
tts_buffer_heap_store_tuple(TupleTableSlot *slot, HeapTuple tuple,
                            Buffer buffer, bool transfer_pin)
{
    BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;

    if (TTS_SHOULDFREE(slot))
    {
        /* materialized slot shouldn't have a buffer to release */
        Assert(!BufferIsValid(bslot->buffer));

        heap_freetuple(bslot->base.tuple);
        slot->tts_flags &= ~TTS_FLAG_SHOULDFREE;
    }

    slot->tts_flags &= ~TTS_FLAG_EMPTY;
    slot->tts_nvalid = 0;
    bslot->base.tuple = tuple;
    bslot->base.off = 0;
    slot->tts_tid = tuple->t_self;

    /*
     * If tuple is on a disk page, keep the page pinned as long as we hold a
     * pointer into it.  We assume the caller already has such a pin.  If
     * transfer_pin is true, we'll transfer that pin to this slot, if not
     * we'll pin it again ourselves.
     *
     * This is coded to optimize the case where the slot previously held a
     * tuple on the same disk page: in that case releasing and re-acquiring
     * the pin is a waste of cycles.  This is a common situation during
     * seqscans, so it's worth troubling over.
     */
    if (bslot->buffer != buffer)
    {
        if (BufferIsValid(bslot->buffer))
            ReleaseBuffer(bslot->buffer);

        bslot->buffer = buffer;

        if (!transfer_pin && BufferIsValid(buffer))
            IncrBufferRefCount(buffer);
    }
    else if (transfer_pin && BufferIsValid(buffer))
    {
        /*
         * In transfer_pin mode the caller won't know about the same-page
         * optimization, so we gotta release its pin.
         */
        ReleaseBuffer(buffer);
    }
}

/*
 * slot_deform_heap_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.
 *
 * This is marked as always inline, so the different offp for different types
 * of slots gets optimized away.
 */
static pg_attribute_always_inline void
slot_deform_heap_tuple(TupleTableSlot *slot, HeapTuple tuple, uint32 *offp,
                       int natts)
{
    TupleDesc   tupleDesc = slot->tts_tupleDescriptor;
    Datum      *values = slot->tts_values;
    bool       *isnull = slot->tts_isnull;
    HeapTupleHeader tup = tuple->t_data;
    bool        hasnulls = HeapTupleHasNulls(tuple);
    int         attnum;
    char       *tp;             /* ptr to tuple data */
    uint32      off;            /* offset in tuple data */
    bits8      *bp = tup->t_bits;   /* ptr to null bitmap in tuple */
    bool        slow;           /* can we use/set attcacheoff? */

    /* We can only fetch as many attributes as the tuple has. */
    natts = Min(HeapTupleHeaderGetNatts(tuple->t_data), natts);

    /*
     * 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 = *offp;
        slow = TTS_SLOW(slot);
    }

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

    for (; attnum < natts; attnum++)
    {
        Form_pg_attribute thisatt = TupleDescAttr(tupleDesc, 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;
    *offp = off;
    if (slow)
        slot->tts_flags |= TTS_FLAG_SLOW;
    else
        slot->tts_flags &= ~TTS_FLAG_SLOW;
}


const TupleTableSlotOps TTSOpsVirtual = {
    .base_slot_size = sizeof(VirtualTupleTableSlot),
    .init = tts_virtual_init,
    .release = tts_virtual_release,
    .clear = tts_virtual_clear,
    .getsomeattrs = tts_virtual_getsomeattrs,
    .getsysattr = tts_virtual_getsysattr,
    .materialize = tts_virtual_materialize,
    .copyslot = tts_virtual_copyslot,

    /*
     * A virtual tuple table slot can not "own" a heap tuple or a minimal
     * tuple.
     */
    .get_heap_tuple = NULL,
    .get_minimal_tuple = NULL,
    .copy_heap_tuple = tts_virtual_copy_heap_tuple,
    .copy_minimal_tuple = tts_virtual_copy_minimal_tuple
};

const TupleTableSlotOps TTSOpsHeapTuple = {
    .base_slot_size = sizeof(HeapTupleTableSlot),
    .init = tts_heap_init,
    .release = tts_heap_release,
    .clear = tts_heap_clear,
    .getsomeattrs = tts_heap_getsomeattrs,
    .getsysattr = tts_heap_getsysattr,
    .materialize = tts_heap_materialize,
    .copyslot = tts_heap_copyslot,
    .get_heap_tuple = tts_heap_get_heap_tuple,

    /* A heap tuple table slot can not "own" a minimal tuple. */
    .get_minimal_tuple = NULL,
    .copy_heap_tuple = tts_heap_copy_heap_tuple,
    .copy_minimal_tuple = tts_heap_copy_minimal_tuple
};

const TupleTableSlotOps TTSOpsMinimalTuple = {
    .base_slot_size = sizeof(MinimalTupleTableSlot),
    .init = tts_minimal_init,
    .release = tts_minimal_release,
    .clear = tts_minimal_clear,
    .getsomeattrs = tts_minimal_getsomeattrs,
    .getsysattr = tts_minimal_getsysattr,
    .materialize = tts_minimal_materialize,
    .copyslot = tts_minimal_copyslot,

    /* A minimal tuple table slot can not "own" a heap tuple. */
    .get_heap_tuple = NULL,
    .get_minimal_tuple = tts_minimal_get_minimal_tuple,
    .copy_heap_tuple = tts_minimal_copy_heap_tuple,
    .copy_minimal_tuple = tts_minimal_copy_minimal_tuple
};

const TupleTableSlotOps TTSOpsBufferHeapTuple = {
    .base_slot_size = sizeof(BufferHeapTupleTableSlot),
    .init = tts_buffer_heap_init,
    .release = tts_buffer_heap_release,
    .clear = tts_buffer_heap_clear,
    .getsomeattrs = tts_buffer_heap_getsomeattrs,
    .getsysattr = tts_buffer_heap_getsysattr,
    .materialize = tts_buffer_heap_materialize,
    .copyslot = tts_buffer_heap_copyslot,
    .get_heap_tuple = tts_buffer_heap_get_heap_tuple,

    /* A buffer heap tuple table slot can not "own" a minimal tuple. */
    .get_minimal_tuple = NULL,
    .copy_heap_tuple = tts_buffer_heap_copy_heap_tuple,
    .copy_minimal_tuple = tts_buffer_heap_copy_minimal_tuple
};


/* ----------------------------------------------------------------
 *                tuple table create/delete functions
 * ----------------------------------------------------------------
 */

/* --------------------------------
 *      MakeTupleTableSlot
 *
 *      Basic routine to make an empty TupleTableSlot of given
 *      TupleTableSlotType. If tupleDesc is specified the slot's descriptor is
 *      fixed for its lifetime, gaining some efficiency. If that's
 *      undesirable, pass NULL.
 * --------------------------------
 */
TupleTableSlot *
MakeTupleTableSlot(TupleDesc tupleDesc,
                   const TupleTableSlotOps *tts_ops)
{
    Size        basesz,
                allocsz;
    TupleTableSlot *slot;

    basesz = tts_ops->base_slot_size;

    /*
     * When a fixed descriptor is specified, we can reduce overhead by
     * allocating the entire slot in one go.
     */
    if (tupleDesc)
        allocsz = MAXALIGN(basesz) +
            MAXALIGN(tupleDesc->natts * sizeof(Datum)) +
            MAXALIGN(tupleDesc->natts * sizeof(bool));
    else
        allocsz = basesz;

    slot = palloc0(allocsz);
    /* const for optimization purposes, OK to modify at allocation time */
    *((const TupleTableSlotOps **) &slot->tts_ops) = tts_ops;
    slot->type = T_TupleTableSlot;
    slot->tts_flags |= TTS_FLAG_EMPTY;
    if (tupleDesc != NULL)
        slot->tts_flags |= TTS_FLAG_FIXED;
    slot->tts_tupleDescriptor = tupleDesc;
    slot->tts_mcxt = CurrentMemoryContext;
    slot->tts_nvalid = 0;

    if (tupleDesc != NULL)
    {
        slot->tts_values = (Datum *)
            (((char *) slot)
             + MAXALIGN(basesz));
        slot->tts_isnull = (bool *)
            (((char *) slot)
             + MAXALIGN(basesz)
             + MAXALIGN(tupleDesc->natts * sizeof(Datum)));

        PinTupleDesc(tupleDesc);
    }

    /*
     * And allow slot type specific initialization.
     */
    slot->tts_ops->init(slot);

    return slot;
}

/* --------------------------------
 *      ExecAllocTableSlot
 *
 *      Create a tuple table slot within a tuple table (which is just a List).
 * --------------------------------
 */
TupleTableSlot *
ExecAllocTableSlot(List **tupleTable, TupleDesc desc,
                   const TupleTableSlotOps *tts_ops)
{
    TupleTableSlot *slot = MakeTupleTableSlot(desc, tts_ops);

    *tupleTable = lappend(*tupleTable, slot);

    return slot;
}

/* --------------------------------
 *      ExecResetTupleTable
 *
 *      This releases any resources (buffer pins, tupdesc refcounts)
 *      held by the tuple table, and optionally releases the memory
 *      occupied by the tuple table data structure.
 *      It is expected that this routine be called by ExecEndPlan().
 * --------------------------------
 */
void
ExecResetTupleTable(List *tupleTable,   /* tuple table */
                    bool shouldFree)    /* true if we should free memory */
{
    ListCell   *lc;

    foreach(lc, tupleTable)
    {
        TupleTableSlot *slot = lfirst_node(TupleTableSlot, lc);

        /* Always release resources and reset the slot to empty */
        ExecClearTuple(slot);
        slot->tts_ops->release(slot);
        if (slot->tts_tupleDescriptor)
        {
            ReleaseTupleDesc(slot->tts_tupleDescriptor);
            slot->tts_tupleDescriptor = NULL;
        }

        /* If shouldFree, release memory occupied by the slot itself */
        if (shouldFree)
        {
            if (!TTS_FIXED(slot))
            {
                if (slot->tts_values)
                    pfree(slot->tts_values);
                if (slot->tts_isnull)
                    pfree(slot->tts_isnull);
            }
            pfree(slot);
        }
    }

    /* If shouldFree, release the list structure */
    if (shouldFree)
        list_free(tupleTable);
}

/* --------------------------------
 *      MakeSingleTupleTableSlot
 *
 *      This is a convenience routine for operations that need a standalone
 *      TupleTableSlot not gotten from the main executor tuple table.  It makes
 *      a single slot of given TupleTableSlotType and initializes it to use the
 *      given tuple descriptor.
 * --------------------------------
 */
TupleTableSlot *
MakeSingleTupleTableSlot(TupleDesc tupdesc,
                         const TupleTableSlotOps *tts_ops)
{
    TupleTableSlot *slot = MakeTupleTableSlot(tupdesc, tts_ops);

    return slot;
}

/* --------------------------------
 *      ExecDropSingleTupleTableSlot
 *
 *      Release a TupleTableSlot made with MakeSingleTupleTableSlot.
 *      DON'T use this on a slot that's part of a tuple table list!
 * --------------------------------
 */
void
ExecDropSingleTupleTableSlot(TupleTableSlot *slot)
{
    /* This should match ExecResetTupleTable's processing of one slot */
    Assert(IsA(slot, TupleTableSlot));
    ExecClearTuple(slot);
    slot->tts_ops->release(slot);
    if (slot->tts_tupleDescriptor)
        ReleaseTupleDesc(slot->tts_tupleDescriptor);
    if (!TTS_FIXED(slot))
    {
        if (slot->tts_values)
            pfree(slot->tts_values);
        if (slot->tts_isnull)
            pfree(slot->tts_isnull);
    }
    pfree(slot);
}


/* ----------------------------------------------------------------
 *                tuple table slot accessor functions
 * ----------------------------------------------------------------
 */

/* --------------------------------
 *      ExecSetSlotDescriptor
 *
 *      This function is used to set the tuple descriptor associated
 *      with the slot's tuple.  The passed descriptor must have lifespan
 *      at least equal to the slot's.  If it is a reference-counted descriptor
 *      then the reference count is incremented for as long as the slot holds
 *      a reference.
 * --------------------------------
 */
void
ExecSetSlotDescriptor(TupleTableSlot *slot, /* slot to change */
                      TupleDesc tupdesc)    /* new tuple descriptor */
{
    Assert(!TTS_FIXED(slot));

    /* For safety, make sure slot is empty before changing it */
    ExecClearTuple(slot);

    /*
     * Release any old descriptor.  Also release old Datum/isnull arrays if
     * present (we don't bother to check if they could be re-used).
     */
    if (slot->tts_tupleDescriptor)
        ReleaseTupleDesc(slot->tts_tupleDescriptor);

    if (slot->tts_values)
        pfree(slot->tts_values);
    if (slot->tts_isnull)
        pfree(slot->tts_isnull);

    /*
     * Install the new descriptor; if it's refcounted, bump its refcount.
     */
    slot->tts_tupleDescriptor = tupdesc;
    PinTupleDesc(tupdesc);

    /*
     * Allocate Datum/isnull arrays of the appropriate size.  These must have
     * the same lifetime as the slot, so allocate in the slot's own context.
     */
    slot->tts_values = (Datum *)
        MemoryContextAlloc(slot->tts_mcxt, tupdesc->natts * sizeof(Datum));
    slot->tts_isnull = (bool *)
        MemoryContextAlloc(slot->tts_mcxt, tupdesc->natts * sizeof(bool));
}

/* --------------------------------
 *      ExecStoreHeapTuple
 *
 *      This function is used to store an on-the-fly physical tuple into a specified
 *      slot in the tuple table.
 *
 *      tuple:  tuple to store
 *      slot:   TTSOpsHeapTuple type slot to store it in
 *      shouldFree: true if ExecClearTuple should pfree() the tuple
 *                  when done with it
 *
 * shouldFree is normally set 'true' for tuples constructed on-the-fly.  But it
 * can be 'false' when the referenced tuple is held in a tuple table slot
 * belonging to a lower-level executor Proc node.  In this case the lower-level
 * slot retains ownership and responsibility for eventually releasing the
 * tuple.  When this method is used, we must be certain that the upper-level
 * Proc node will lose interest in the tuple sooner than the lower-level one
 * does!  If you're not certain, copy the lower-level tuple with heap_copytuple
 * and let the upper-level table slot assume ownership of the copy!
 *
 * Return value is just the passed-in slot pointer.
 *
 * If the target slot is not guaranteed to be TTSOpsHeapTuple type slot, use
 * the, more expensive, ExecForceStoreHeapTuple().
 * --------------------------------
 */
TupleTableSlot *
ExecStoreHeapTuple(HeapTuple tuple,
                   TupleTableSlot *slot,
                   bool shouldFree)
{
    /*
     * sanity checks
     */
    Assert(tuple != NULL);
    Assert(slot != NULL);
    Assert(slot->tts_tupleDescriptor != NULL);

    if (unlikely(!TTS_IS_HEAPTUPLE(slot)))
        elog(ERROR, "trying to store a heap tuple into wrong type of slot");
    tts_heap_store_tuple(slot, tuple, shouldFree);

    slot->tts_tableOid = tuple->t_tableOid;

    return slot;
}

/* --------------------------------
 *      ExecStoreBufferHeapTuple
 *
 *      This function is used to store an on-disk physical tuple from a buffer
 *      into a specified slot in the tuple table.
 *
 *      tuple:  tuple to store
 *      slot:   TTSOpsBufferHeapTuple type slot to store it in
 *      buffer: disk buffer if tuple is in a disk page, else InvalidBuffer
 *
 * The tuple table code acquires a pin on the buffer which is held until the
 * slot is cleared, so that the tuple won't go away on us.
 *
 * Return value is just the passed-in slot pointer.
 *
 * If the target slot is not guaranteed to be TTSOpsBufferHeapTuple type slot,
 * use the, more expensive, ExecForceStoreHeapTuple().
 * --------------------------------
 */
TupleTableSlot *
ExecStoreBufferHeapTuple(HeapTuple tuple,
                         TupleTableSlot *slot,
                         Buffer buffer)
{
    /*
     * sanity checks
     */
    Assert(tuple != NULL);
    Assert(slot != NULL);
    Assert(slot->tts_tupleDescriptor != NULL);
    Assert(BufferIsValid(buffer));

    if (unlikely(!TTS_IS_BUFFERTUPLE(slot)))
        elog(ERROR, "trying to store an on-disk heap tuple into wrong type of slot");
    tts_buffer_heap_store_tuple(slot, tuple, buffer, false);

    slot->tts_tableOid = tuple->t_tableOid;

    return slot;
}

/*
 * Like ExecStoreBufferHeapTuple, but transfer an existing pin from the caller
 * to the slot, i.e. the caller doesn't need to, and may not, release the pin.
 */
TupleTableSlot *
ExecStorePinnedBufferHeapTuple(HeapTuple tuple,
                               TupleTableSlot *slot,
                               Buffer buffer)
{
    /*
     * sanity checks
     */
    Assert(tuple != NULL);
    Assert(slot != NULL);
    Assert(slot->tts_tupleDescriptor != NULL);
    Assert(BufferIsValid(buffer));

    if (unlikely(!TTS_IS_BUFFERTUPLE(slot)))
        elog(ERROR, "trying to store an on-disk heap tuple into wrong type of slot");
    tts_buffer_heap_store_tuple(slot, tuple, buffer, true);

    slot->tts_tableOid = tuple->t_tableOid;

    return slot;
}

/*
 * Store a minimal tuple into TTSOpsMinimalTuple type slot.
 *
 * If the target slot is not guaranteed to be TTSOpsMinimalTuple type slot,
 * use the, more expensive, ExecForceStoreMinimalTuple().
 */
TupleTableSlot *
ExecStoreMinimalTuple(MinimalTuple mtup,
                      TupleTableSlot *slot,
                      bool shouldFree)
{
    /*
     * sanity checks
     */
    Assert(mtup != NULL);
    Assert(slot != NULL);
    Assert(slot->tts_tupleDescriptor != NULL);

    if (unlikely(!TTS_IS_MINIMALTUPLE(slot)))
        elog(ERROR, "trying to store a minimal tuple into wrong type of slot");
    tts_minimal_store_tuple(slot, mtup, shouldFree);

    return slot;
}

/*
 * Store a HeapTuple into any kind of slot, performing conversion if
 * necessary.
 */
void
ExecForceStoreHeapTuple(HeapTuple tuple,
                        TupleTableSlot *slot,
                        bool shouldFree)
{
    if (TTS_IS_HEAPTUPLE(slot))
    {
        ExecStoreHeapTuple(tuple, slot, shouldFree);
    }
    else if (TTS_IS_BUFFERTUPLE(slot))
    {
        MemoryContext oldContext;
        BufferHeapTupleTableSlot *bslot = (BufferHeapTupleTableSlot *) slot;

        ExecClearTuple(slot);
        slot->tts_flags &= ~TTS_FLAG_EMPTY;
        oldContext = MemoryContextSwitchTo(slot->tts_mcxt);
        bslot->base.tuple = heap_copytuple(tuple);
        slot->tts_flags |= TTS_FLAG_SHOULDFREE;
        MemoryContextSwitchTo(oldContext);

        if (shouldFree)
            pfree(tuple);
    }
    else
    {
        ExecClearTuple(slot);
        heap_deform_tuple(tuple, slot->tts_tupleDescriptor,
                          slot->tts_values, slot->tts_isnull);
        ExecStoreVirtualTuple(slot);

        if (shouldFree)
        {
            ExecMaterializeSlot(slot);
            pfree(tuple);
        }
    }
}

/*
 * Store a MinimalTuple into any kind of slot, performing conversion if
 * necessary.
 */
void
ExecForceStoreMinimalTuple(MinimalTuple mtup,
                           TupleTableSlot *slot,
                           bool shouldFree)
{
    if (TTS_IS_MINIMALTUPLE(slot))
    {
        tts_minimal_store_tuple(slot, mtup, shouldFree);
    }
    else
    {
        HeapTupleData htup;

        ExecClearTuple(slot);

        htup.t_len = mtup->t_len + MINIMAL_TUPLE_OFFSET;
        htup.t_data = (HeapTupleHeader) ((char *) mtup - MINIMAL_TUPLE_OFFSET);
        heap_deform_tuple(&htup, slot->tts_tupleDescriptor,
                          slot->tts_values, slot->tts_isnull);
        ExecStoreVirtualTuple(slot);

        if (shouldFree)
        {
            ExecMaterializeSlot(slot);
            pfree(mtup);
        }
    }
}

/* --------------------------------
 *      ExecStoreVirtualTuple
 *          Mark a slot as containing a virtual tuple.
 *
 * The protocol for loading a slot with virtual tuple data is:
 *      * Call ExecClearTuple to mark the slot empty.
 *      * Store data into the Datum/isnull arrays.
 *      * Call ExecStoreVirtualTuple to mark the slot valid.
 * This is a bit unclean but it avoids one round of data copying.
 * --------------------------------
 */
TupleTableSlot *
ExecStoreVirtualTuple(TupleTableSlot *slot)
{
    /*
     * sanity checks
     */
    Assert(slot != NULL);
    Assert(slot->tts_tupleDescriptor != NULL);
    Assert(TTS_EMPTY(slot));

    slot->tts_flags &= ~TTS_FLAG_EMPTY;
    slot->tts_nvalid = slot->tts_tupleDescriptor->natts;

    return slot;
}

/* --------------------------------
 *      ExecStoreAllNullTuple
 *          Set up the slot to contain a null in every column.
 *
 * At first glance this might sound just like ExecClearTuple, but it's
 * entirely different: the slot ends up full, not empty.
 * --------------------------------
 */
TupleTableSlot *
ExecStoreAllNullTuple(TupleTableSlot *slot)
{
    /*
     * sanity checks
     */
    Assert(slot != NULL);
    Assert(slot->tts_tupleDescriptor != NULL);

    /* Clear any old contents */
    ExecClearTuple(slot);

    /*
     * Fill all the columns of the virtual tuple with nulls
     */
    MemSet(slot->tts_values, 0,
           slot->tts_tupleDescriptor->natts * sizeof(Datum));
    memset(slot->tts_isnull, true,
           slot->tts_tupleDescriptor->natts * sizeof(bool));

    return ExecStoreVirtualTuple(slot);
}

/*
 * Store a HeapTuple in datum form, into a slot. That always requires
 * deforming it and storing it in virtual form.
 *
 * Until the slot is materialized, the contents of the slot depend on the
 * datum.
 */
void
ExecStoreHeapTupleDatum(Datum data, TupleTableSlot *slot)
{
    HeapTupleData tuple = {0};
    HeapTupleHeader td;

    td = DatumGetHeapTupleHeader(data);

    tuple.t_len = HeapTupleHeaderGetDatumLength(td);
    tuple.t_self = td->t_ctid;
    tuple.t_data = td;

    ExecClearTuple(slot);

    heap_deform_tuple(&tuple, slot->tts_tupleDescriptor,
                      slot->tts_values, slot->tts_isnull);
    ExecStoreVirtualTuple(slot);
}

/*
 * ExecFetchSlotHeapTuple - fetch HeapTuple representing the slot's content
 *
 * The returned HeapTuple represents the slot's content as closely as
 * possible.
 *
 * If materialize is true, the contents of the slots will be made independent
 * from the underlying storage (i.e. all buffer pins are released, memory is
 * allocated in the slot's context).
 *
 * If shouldFree is not-NULL it'll be set to true if the returned tuple has
 * been allocated in the calling memory context, and must be freed by the
 * caller (via explicit pfree() or a memory context reset).
 *
 * NB: If materialize is true, modifications of the returned tuple are
 * allowed. But it depends on the type of the slot whether such modifications
 * will also affect the slot's contents. While that is not the nicest
 * behaviour, all such modifications are in the process of being removed.
 */
HeapTuple
ExecFetchSlotHeapTuple(TupleTableSlot *slot, bool materialize, bool *shouldFree)
{
    /*
     * sanity checks
     */
    Assert(slot != NULL);
    Assert(!TTS_EMPTY(slot));

    /* Materialize the tuple so that the slot "owns" it, if requested. */
    if (materialize)
        slot->tts_ops->materialize(slot);

    if (slot->tts_ops->get_heap_tuple == NULL)
    {
        if (shouldFree)
            *shouldFree = true;
        return slot->tts_ops->copy_heap_tuple(slot);
    }
    else
    {
        if (shouldFree)
            *shouldFree = false;
        return slot->tts_ops->get_heap_tuple(slot);
    }
}

/* --------------------------------
 *      ExecFetchSlotMinimalTuple
 *          Fetch the slot's minimal physical tuple.
 *
 *      If the given tuple table slot can hold a minimal tuple, indicated by a
 *      non-NULL get_minimal_tuple callback, the function returns the minimal
 *      tuple returned by that callback. It assumes that the minimal tuple
 *      returned by the callback is "owned" by the slot i.e. the slot is
 *      responsible for freeing the memory consumed by the tuple. Hence it sets
 *      *shouldFree to false, indicating that the caller should not free the
 *      memory consumed by the minimal tuple. In this case the returned minimal
 *      tuple should be considered as read-only.
 *
 *      If that callback is not supported, it calls copy_minimal_tuple callback
 *      which is expected to return a copy of minimal tuple representing the
 *      contents of the slot. In this case *shouldFree is set to true,
 *      indicating the caller that it should free the memory consumed by the
 *      minimal tuple. In this case the returned minimal tuple may be written
 *      up.
 * --------------------------------
 */
MinimalTuple
ExecFetchSlotMinimalTuple(TupleTableSlot *slot,
                          bool *shouldFree)
{
    /*
     * sanity checks
     */
    Assert(slot != NULL);
    Assert(!TTS_EMPTY(slot));

    if (slot->tts_ops->get_minimal_tuple)
    {
        if (shouldFree)
            *shouldFree = false;
        return slot->tts_ops->get_minimal_tuple(slot);
    }
    else
    {
        if (shouldFree)
            *shouldFree = true;
        return slot->tts_ops->copy_minimal_tuple(slot);
    }
}

/* --------------------------------
 *      ExecFetchSlotHeapTupleDatum
 *          Fetch the slot's tuple as a composite-type Datum.
 *
 *      The result is always freshly palloc'd in the caller's memory context.
 * --------------------------------
 */
Datum
ExecFetchSlotHeapTupleDatum(TupleTableSlot *slot)
{
    HeapTuple   tup;
    TupleDesc   tupdesc;
    bool        shouldFree;
    Datum       ret;

    /* Fetch slot's contents in regular-physical-tuple form */
    tup = ExecFetchSlotHeapTuple(slot, false, &shouldFree);
    tupdesc = slot->tts_tupleDescriptor;

    /* Convert to Datum form */
    ret = heap_copy_tuple_as_datum(tup, tupdesc);

    if (shouldFree)
        pfree(tup);

    return ret;
}

/* ----------------------------------------------------------------
 *              convenience initialization routines
 * ----------------------------------------------------------------
 */

/* ----------------
 *      ExecInitResultTypeTL
 *
 *      Initialize result type, using the plan node's targetlist.
 * ----------------
 */
void
ExecInitResultTypeTL(PlanState *planstate)
{
    TupleDesc   tupDesc = ExecTypeFromTL(planstate->plan->targetlist);

    planstate->ps_ResultTupleDesc = tupDesc;
}

/* --------------------------------
 *      ExecInit{Result,Scan,Extra}TupleSlot[TL]
 *
 *      These are convenience routines to initialize the specified slot
 *      in nodes inheriting the appropriate state.  ExecInitExtraTupleSlot
 *      is used for initializing special-purpose slots.
 * --------------------------------
 */

/* ----------------
 *      ExecInitResultTupleSlotTL
 *
 *      Initialize result tuple slot, using the tuple descriptor previously
 *      computed with ExecInitResultTypeTL().
 * ----------------
 */
void
ExecInitResultSlot(PlanState *planstate, const TupleTableSlotOps *tts_ops)
{
    TupleTableSlot *slot;

    slot = ExecAllocTableSlot(&planstate->state->es_tupleTable,
                              planstate->ps_ResultTupleDesc, tts_ops);
    planstate->ps_ResultTupleSlot = slot;

    planstate->resultopsfixed = planstate->ps_ResultTupleDesc != NULL;
    planstate->resultops = tts_ops;
    planstate->resultopsset = true;
}

/* ----------------
 *      ExecInitResultTupleSlotTL
 *
 *      Initialize result tuple slot, using the plan node's targetlist.
 * ----------------
 */
void
ExecInitResultTupleSlotTL(PlanState *planstate,
                          const TupleTableSlotOps *tts_ops)
{
    ExecInitResultTypeTL(planstate);
    ExecInitResultSlot(planstate, tts_ops);
}

/* ----------------
 *      ExecInitScanTupleSlot
 * ----------------
 */
void
ExecInitScanTupleSlot(EState *estate, ScanState *scanstate,
                      TupleDesc tupledesc, const TupleTableSlotOps *tts_ops)
{
    scanstate->ss_ScanTupleSlot = ExecAllocTableSlot(&estate->es_tupleTable,
                                                     tupledesc, tts_ops);
    scanstate->ps.scandesc = tupledesc;
    scanstate->ps.scanopsfixed = tupledesc != NULL;
    scanstate->ps.scanops = tts_ops;
    scanstate->ps.scanopsset = true;
}

/* ----------------
 *      ExecInitExtraTupleSlot
 *
 * Return a newly created slot. If tupledesc is non-NULL the slot will have
 * that as its fixed tupledesc. Otherwise the caller needs to use
 * ExecSetSlotDescriptor() to set the descriptor before use.
 * ----------------
 */
TupleTableSlot *
ExecInitExtraTupleSlot(EState *estate,
                       TupleDesc tupledesc,
                       const TupleTableSlotOps *tts_ops)
{
    return ExecAllocTableSlot(&estate->es_tupleTable, tupledesc, tts_ops);
}

/* ----------------
 *      ExecInitNullTupleSlot
 *
 * Build a slot containing an all-nulls tuple of the given type.
 * This is used as a substitute for an input tuple when performing an
 * outer join.
 * ----------------
 */
TupleTableSlot *
ExecInitNullTupleSlot(EState *estate, TupleDesc tupType,
                      const TupleTableSlotOps *tts_ops)
{
    TupleTableSlot *slot = ExecInitExtraTupleSlot(estate, tupType, tts_ops);

    return ExecStoreAllNullTuple(slot);
}

/* ---------------------------------------------------------------
 *      Routines for setting/accessing attributes in a slot.
 * ---------------------------------------------------------------
 */

/*
 * Fill in missing values for a TupleTableSlot.
 *
 * This is only exposed because it's needed for JIT compiled tuple
 * deforming. That exception aside, there should be no callers outside of this
 * file.
 */
void
slot_getmissingattrs(TupleTableSlot *slot, int startAttNum, int lastAttNum)
{
    AttrMissing *attrmiss = NULL;

    if (slot->tts_tupleDescriptor->constr)
        attrmiss = slot->tts_tupleDescriptor->constr->missing;

    if (!attrmiss)
    {
        /* no missing values array at all, so just fill everything in as NULL */
        memset(slot->tts_values + startAttNum, 0,
               (lastAttNum - startAttNum) * sizeof(Datum));
        memset(slot->tts_isnull + startAttNum, 1,
               (lastAttNum - startAttNum) * sizeof(bool));
    }
    else
    {
        int         missattnum;

        /* if there is a missing values array we must process them one by one */
        for (missattnum = startAttNum;
             missattnum < lastAttNum;
             missattnum++)
        {
            slot->tts_values[missattnum] = attrmiss[missattnum].am_value;
            slot->tts_isnull[missattnum] = !attrmiss[missattnum].am_present;
        }
    }
}

/*
 * slot_getsomeattrs_int - workhorse for slot_getsomeattrs()
 */
void
slot_getsomeattrs_int(TupleTableSlot *slot, int attnum)
{
    /* Check for caller errors */
    Assert(slot->tts_nvalid < attnum);  /* checked in slot_getsomeattrs */
    Assert(attnum > 0);

    if (unlikely(attnum > slot->tts_tupleDescriptor->natts))
        elog(ERROR, "invalid attribute number %d", attnum);

    /* Fetch as many attributes as possible from the underlying tuple. */
    slot->tts_ops->getsomeattrs(slot, attnum);

    /*
     * If the underlying tuple doesn't have enough attributes, tuple
     * descriptor must have the missing attributes.
     */
    if (unlikely(slot->tts_nvalid < attnum))
    {
        slot_getmissingattrs(slot, slot->tts_nvalid, attnum);
        slot->tts_nvalid = attnum;
    }
}

/* ----------------------------------------------------------------
 *      ExecTypeFromTL
 *
 *      Generate a tuple descriptor for the result tuple of a targetlist.
 *      (A parse/plan tlist must be passed, not an ExprState tlist.)
 *      Note that resjunk columns, if any, are included in the result.
 *
 *      Currently there are about 4 different places where we create
 *      TupleDescriptors.  They should all be merged, or perhaps
 *      be rewritten to call BuildDesc().
 * ----------------------------------------------------------------
 */
TupleDesc
ExecTypeFromTL(List *targetList)
{
    return ExecTypeFromTLInternal(targetList, false);
}

/* ----------------------------------------------------------------
 *      ExecCleanTypeFromTL
 *
 *      Same as above, but resjunk columns are omitted from the result.
 * ----------------------------------------------------------------
 */
TupleDesc
ExecCleanTypeFromTL(List *targetList)
{
    return ExecTypeFromTLInternal(targetList, true);
}

static TupleDesc
ExecTypeFromTLInternal(List *targetList, bool skipjunk)
{
    TupleDesc   typeInfo;
    ListCell   *l;
    int         len;
    int         cur_resno = 1;

    if (skipjunk)
        len = ExecCleanTargetListLength(targetList);
    else
        len = ExecTargetListLength(targetList);
    typeInfo = CreateTemplateTupleDesc(len);

    foreach(l, targetList)
    {
        TargetEntry *tle = lfirst(l);

        if (skipjunk && tle->resjunk)
            continue;
        TupleDescInitEntry(typeInfo,
                           cur_resno,
                           tle->resname,
                           exprType((Node *) tle->expr),
                           exprTypmod((Node *) tle->expr),
                           0);
        TupleDescInitEntryCollation(typeInfo,
                                    cur_resno,
                                    exprCollation((Node *) tle->expr));
        cur_resno++;
    }

    return typeInfo;
}

/*
 * ExecTypeFromExprList - build a tuple descriptor from a list of Exprs
 *
 * This is roughly like ExecTypeFromTL, but we work from bare expressions
 * not TargetEntrys.  No names are attached to the tupledesc's columns.
 */
TupleDesc
ExecTypeFromExprList(List *exprList)
{
    TupleDesc   typeInfo;
    ListCell   *lc;
    int         cur_resno = 1;

    typeInfo = CreateTemplateTupleDesc(list_length(exprList));

    foreach(lc, exprList)
    {
        Node       *e = lfirst(lc);

        TupleDescInitEntry(typeInfo,
                           cur_resno,
                           NULL,
                           exprType(e),
                           exprTypmod(e),
                           0);
        TupleDescInitEntryCollation(typeInfo,
                                    cur_resno,
                                    exprCollation(e));
        cur_resno++;
    }

    return typeInfo;
}

/*
 * ExecTypeSetColNames - set column names in a TupleDesc
 *
 * Column names must be provided as an alias list (list of String nodes).
 *
 * For some callers, the supplied tupdesc has a named rowtype (not RECORD)
 * and it is moderately likely that the alias list matches the column names
 * already present in the tupdesc.  If we do change any column names then
 * we must reset the tupdesc's type to anonymous RECORD; but we avoid doing
 * so if no names change.
 */
void
ExecTypeSetColNames(TupleDesc typeInfo, List *namesList)
{
    bool        modified = false;
    int         colno = 0;
    ListCell   *lc;

    foreach(lc, namesList)
    {
        char       *cname = strVal(lfirst(lc));
        Form_pg_attribute attr;

        /* Guard against too-long names list */
        if (colno >= typeInfo->natts)
            break;
        attr = TupleDescAttr(typeInfo, colno);
        colno++;

        /* Ignore empty aliases (these must be for dropped columns) */
        if (cname[0] == '\0')
            continue;

        /* Change tupdesc only if alias is actually different */
        if (strcmp(cname, NameStr(attr->attname)) != 0)
        {
            namestrcpy(&(attr->attname), cname);
            modified = true;
        }
    }

    /* If we modified the tupdesc, it's now a new record type */
    if (modified)
    {
        typeInfo->tdtypeid = RECORDOID;
        typeInfo->tdtypmod = -1;
    }
}

/*
 * BlessTupleDesc - make a completed tuple descriptor useful for SRFs
 *
 * Rowtype Datums returned by a function must contain valid type information.
 * This happens "for free" if the tupdesc came from a relcache entry, but
 * not if we have manufactured a tupdesc for a transient RECORD datatype.
 * In that case we have to notify typcache.c of the existence of the type.
 */
TupleDesc
BlessTupleDesc(TupleDesc tupdesc)
{
    if (tupdesc->tdtypeid == RECORDOID &&
        tupdesc->tdtypmod < 0)
        assign_record_type_typmod(tupdesc);

    return tupdesc;             /* just for notational convenience */
}

/*
 * TupleDescGetAttInMetadata - Build an AttInMetadata structure based on the
 * supplied TupleDesc. AttInMetadata can be used in conjunction with C strings
 * to produce a properly formed tuple.
 */
AttInMetadata *
TupleDescGetAttInMetadata(TupleDesc tupdesc)
{
    int         natts = tupdesc->natts;
    int         i;
    Oid         atttypeid;
    Oid         attinfuncid;
    FmgrInfo   *attinfuncinfo;
    Oid        *attioparams;
    int32      *atttypmods;
    AttInMetadata *attinmeta;

    attinmeta = (AttInMetadata *) palloc(sizeof(AttInMetadata));

    /* "Bless" the tupledesc so that we can make rowtype datums with it */
    attinmeta->tupdesc = BlessTupleDesc(tupdesc);

    /*
     * Gather info needed later to call the "in" function for each attribute
     */
    attinfuncinfo = (FmgrInfo *) palloc0(natts * sizeof(FmgrInfo));
    attioparams = (Oid *) palloc0(natts * sizeof(Oid));
    atttypmods = (int32 *) palloc0(natts * sizeof(int32));

    for (i = 0; i < natts; i++)
    {
        Form_pg_attribute att = TupleDescAttr(tupdesc, i);

        /* Ignore dropped attributes */
        if (!att->attisdropped)
        {
            atttypeid = att->atttypid;
            getTypeInputInfo(atttypeid, &attinfuncid, &attioparams[i]);
            fmgr_info(attinfuncid, &attinfuncinfo[i]);
            atttypmods[i] = att->atttypmod;
        }
    }
    attinmeta->attinfuncs = attinfuncinfo;
    attinmeta->attioparams = attioparams;
    attinmeta->atttypmods = atttypmods;

    return attinmeta;
}

/*
 * BuildTupleFromCStrings - build a HeapTuple given user data in C string form.
 * values is an array of C strings, one for each attribute of the return tuple.
 * A NULL string pointer indicates we want to create a NULL field.
 */
HeapTuple
BuildTupleFromCStrings(AttInMetadata *attinmeta, char **values)
{
    TupleDesc   tupdesc = attinmeta->tupdesc;
    int         natts = tupdesc->natts;
    Datum      *dvalues;
    bool       *nulls;
    int         i;
    HeapTuple   tuple;

    dvalues = (Datum *) palloc(natts * sizeof(Datum));
    nulls = (bool *) palloc(natts * sizeof(bool));

    /*
     * Call the "in" function for each non-dropped attribute, even for nulls,
     * to support domains.
     */
    for (i = 0; i < natts; i++)
    {
        if (!TupleDescAttr(tupdesc, i)->attisdropped)
        {
            /* Non-dropped attributes */
            dvalues[i] = InputFunctionCall(&attinmeta->attinfuncs[i],
                                           values[i],
                                           attinmeta->attioparams[i],
                                           attinmeta->atttypmods[i]);
            if (values[i] != NULL)
                nulls[i] = false;
            else
                nulls[i] = true;
        }
        else
        {
            /* Handle dropped attributes by setting to NULL */
            dvalues[i] = (Datum) 0;
            nulls[i] = true;
        }
    }

    /*
     * Form a tuple
     */
    tuple = heap_form_tuple(tupdesc, dvalues, nulls);

    /*
     * Release locally palloc'd space.  XXX would probably be good to pfree
     * values of pass-by-reference datums, as well.
     */
    pfree(dvalues);
    pfree(nulls);

    return tuple;
}

/*
 * HeapTupleHeaderGetDatum - convert a HeapTupleHeader pointer to a Datum.
 *
 * This must *not* get applied to an on-disk tuple; the tuple should be
 * freshly made by heap_form_tuple or some wrapper routine for it (such as
 * BuildTupleFromCStrings).  Be sure also that the tupledesc used to build
 * the tuple has a properly "blessed" rowtype.
 *
 * Formerly this was a macro equivalent to PointerGetDatum, relying on the
 * fact that heap_form_tuple fills in the appropriate tuple header fields
 * for a composite Datum.  However, we now require that composite Datums not
 * contain any external TOAST pointers.  We do not want heap_form_tuple itself
 * to enforce that; more specifically, the rule applies only to actual Datums
 * and not to HeapTuple structures.  Therefore, HeapTupleHeaderGetDatum is
 * now a function that detects whether there are externally-toasted fields
 * and constructs a new tuple with inlined fields if so.  We still need
 * heap_form_tuple to insert the Datum header fields, because otherwise this
 * code would have no way to obtain a tupledesc for the tuple.
 *
 * Note that if we do build a new tuple, it's palloc'd in the current
 * memory context.  Beware of code that changes context between the initial
 * heap_form_tuple/etc call and calling HeapTuple(Header)GetDatum.
 *
 * For performance-critical callers, it could be worthwhile to take extra
 * steps to ensure that there aren't TOAST pointers in the output of
 * heap_form_tuple to begin with.  It's likely however that the costs of the
 * typcache lookup and tuple disassembly/reassembly are swamped by TOAST
 * dereference costs, so that the benefits of such extra effort would be
 * minimal.
 *
 * XXX it would likely be better to create wrapper functions that produce
 * a composite Datum from the field values in one step.  However, there's
 * enough code using the existing APIs that we couldn't get rid of this
 * hack anytime soon.
 */
Datum
HeapTupleHeaderGetDatum(HeapTupleHeader tuple)
{
    Datum       result;
    TupleDesc   tupDesc;

    /* No work if there are no external TOAST pointers in the tuple */
    if (!HeapTupleHeaderHasExternal(tuple))
        return PointerGetDatum(tuple);

    /* Use the type data saved by heap_form_tuple to look up the rowtype */
    tupDesc = lookup_rowtype_tupdesc(HeapTupleHeaderGetTypeId(tuple),
                                     HeapTupleHeaderGetTypMod(tuple));

    /* And do the flattening */
    result = toast_flatten_tuple_to_datum(tuple,
                                          HeapTupleHeaderGetDatumLength(tuple),
                                          tupDesc);

    ReleaseTupleDesc(tupDesc);

    return result;
}


/*
 * Functions for sending tuples to the frontend (or other specified destination)
 * as though it is a SELECT result. These are used by utility commands that
 * need to project directly to the destination and don't need or want full
 * table function capability. Currently used by EXPLAIN and SHOW ALL.
 */
TupOutputState *
begin_tup_output_tupdesc(DestReceiver *dest,
                         TupleDesc tupdesc,
                         const TupleTableSlotOps *tts_ops)
{
    TupOutputState *tstate;

    tstate = (TupOutputState *) palloc(sizeof(TupOutputState));

    tstate->slot = MakeSingleTupleTableSlot(tupdesc, tts_ops);
    tstate->dest = dest;

    tstate->dest->rStartup(tstate->dest, (int) CMD_SELECT, tupdesc);

    return tstate;
}

/*
 * write a single tuple
 */
void
do_tup_output(TupOutputState *tstate, Datum *values, bool *isnull)
{
    TupleTableSlot *slot = tstate->slot;
    int         natts = slot->tts_tupleDescriptor->natts;

    /* make sure the slot is clear */
    ExecClearTuple(slot);

    /* insert data */
    memcpy(slot->tts_values, values, natts * sizeof(Datum));
    memcpy(slot->tts_isnull, isnull, natts * sizeof(bool));

    /* mark slot as containing a virtual tuple */
    ExecStoreVirtualTuple(slot);

    /* send the tuple to the receiver */
    (void) tstate->dest->receiveSlot(slot, tstate->dest);

    /* clean up */
    ExecClearTuple(slot);
}

/*
 * write a chunk of text, breaking at newline characters
 *
 * Should only be used with a single-TEXT-attribute tupdesc.
 */
void
do_text_output_multiline(TupOutputState *tstate, const char *txt)
{
    Datum       values[1];
    bool        isnull[1] = {false};

    while (*txt)
    {
        const char *eol;
        int         len;

        eol = strchr(txt, '\n');
        if (eol)
        {
            len = eol - txt;
            eol++;
        }
        else
        {
            len = strlen(txt);
            eol = txt + len;
        }

        values[0] = PointerGetDatum(cstring_to_text_with_len(txt, len));
        do_tup_output(tstate, values, isnull);
        pfree(DatumGetPointer(values[0]));
        txt = eol;
    }
}

void
end_tup_output(TupOutputState *tstate)
{
    tstate->dest->rShutdown(tstate->dest);
    /* note that destroying the dest is not ours to do */
    ExecDropSingleTupleTableSlot(tstate->slot);
    pfree(tstate);
}