tstoreReceiver.c

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/*-------------------------------------------------------------------------
 *
 * tstoreReceiver.c
 *    An implementation of DestReceiver that stores the result tuples in
 *    a Tuplestore.
 *
 * Optionally, we can force detoasting (but not decompression) of out-of-line
 * toasted values.  This is to support cursors WITH HOLD, which must retain
 * data even if the underlying table is dropped.
 *
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/executor/tstoreReceiver.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/tuptoaster.h"
#include "executor/tstoreReceiver.h"


typedef struct
{
    DestReceiver pub;
    /* parameters: */
    Tuplestorestate *tstore;    /* where to put the data */
    MemoryContext cxt;          /* context containing tstore */
    bool        detoast;        /* were we told to detoast? */
    /* workspace: */
    Datum      *outvalues;      /* values array for result tuple */
    Datum      *tofree;         /* temp values to be pfree'd */
} TStoreState;


static void tstoreReceiveSlot_notoast(TupleTableSlot *slot, DestReceiver *self);
static void tstoreReceiveSlot_detoast(TupleTableSlot *slot, DestReceiver *self);


/*
 * Prepare to receive tuples from executor.
 */
static void
tstoreStartupReceiver(DestReceiver *self, int operation, TupleDesc typeinfo)
{
    TStoreState *myState = (TStoreState *) self;
    bool        needtoast = false;
    Form_pg_attribute *attrs = typeinfo->attrs;
    int         natts = typeinfo->natts;
    int         i;

    /* Check if any columns require detoast work */
    if (myState->detoast)
    {
        for (i = 0; i < natts; i++)
        {
            if (attrs[i]->attisdropped)
                continue;
            if (attrs[i]->attlen == -1)
            {
                needtoast = true;
                break;
            }
        }
    }

    /* Set up appropriate callback */
    if (needtoast)
    {
        myState->pub.receiveSlot = tstoreReceiveSlot_detoast;
        /* Create workspace */
        myState->outvalues = (Datum *)
            MemoryContextAlloc(myState->cxt, natts * sizeof(Datum));
        myState->tofree = (Datum *)
            MemoryContextAlloc(myState->cxt, natts * sizeof(Datum));
    }
    else
    {
        myState->pub.receiveSlot = tstoreReceiveSlot_notoast;
        myState->outvalues = NULL;
        myState->tofree = NULL;
    }
}

/*
 * Receive a tuple from the executor and store it in the tuplestore.
 * This is for the easy case where we don't have to detoast.
 */
static void
tstoreReceiveSlot_notoast(TupleTableSlot *slot, DestReceiver *self)
{
    TStoreState *myState = (TStoreState *) self;

    tuplestore_puttupleslot(myState->tstore, slot);
}

/*
 * Receive a tuple from the executor and store it in the tuplestore.
 * This is for the case where we have to detoast any toasted values.
 */
static void
tstoreReceiveSlot_detoast(TupleTableSlot *slot, DestReceiver *self)
{
    TStoreState *myState = (TStoreState *) self;
    TupleDesc   typeinfo = slot->tts_tupleDescriptor;
    Form_pg_attribute *attrs = typeinfo->attrs;
    int         natts = typeinfo->natts;
    int         nfree;
    int         i;
    MemoryContext oldcxt;

    /* Make sure the tuple is fully deconstructed */
    slot_getallattrs(slot);

    /*
     * Fetch back any out-of-line datums.  We build the new datums array in
     * myState->outvalues[] (but we can re-use the slot's isnull array). Also,
     * remember the fetched values to free afterwards.
     */
    nfree = 0;
    for (i = 0; i < natts; i++)
    {
        Datum       val = slot->tts_values[i];

        if (!attrs[i]->attisdropped &&
            attrs[i]->attlen == -1 &&
            !slot->tts_isnull[i])
        {
            if (VARATT_IS_EXTERNAL(DatumGetPointer(val)))
            {
                val = PointerGetDatum(heap_tuple_fetch_attr((struct varlena *)
                                                      DatumGetPointer(val)));
                myState->tofree[nfree++] = val;
            }
        }

        myState->outvalues[i] = val;
    }

    /*
     * Push the modified tuple into the tuplestore.
     */
    oldcxt = MemoryContextSwitchTo(myState->cxt);
    tuplestore_putvalues(myState->tstore, typeinfo,
                         myState->outvalues, slot->tts_isnull);
    MemoryContextSwitchTo(oldcxt);

    /* And release any temporary detoasted values */
    for (i = 0; i < nfree; i++)
        pfree(DatumGetPointer(myState->tofree[i]));
}

/*
 * Clean up at end of an executor run
 */
static void
tstoreShutdownReceiver(DestReceiver *self)
{
    TStoreState *myState = (TStoreState *) self;

    /* Release workspace if any */
    if (myState->outvalues)
        pfree(myState->outvalues);
    myState->outvalues = NULL;
    if (myState->tofree)
        pfree(myState->tofree);
    myState->tofree = NULL;
}

/*
 * Destroy receiver when done with it
 */
static void
tstoreDestroyReceiver(DestReceiver *self)
{
    pfree(self);
}

/*
 * Initially create a DestReceiver object.
 */
DestReceiver *
CreateTuplestoreDestReceiver(void)
{
    TStoreState *self = (TStoreState *) palloc0(sizeof(TStoreState));

    self->pub.receiveSlot = tstoreReceiveSlot_notoast;  /* might change */
    self->pub.rStartup = tstoreStartupReceiver;
    self->pub.rShutdown = tstoreShutdownReceiver;
    self->pub.rDestroy = tstoreDestroyReceiver;
    self->pub.mydest = DestTuplestore;

    /* private fields will be set by SetTuplestoreDestReceiverParams */

    return (DestReceiver *) self;
}

/*
 * Set parameters for a TuplestoreDestReceiver
 */
void
SetTuplestoreDestReceiverParams(DestReceiver *self,
                                Tuplestorestate *tStore,
                                MemoryContext tContext,
                                bool detoast)
{
    TStoreState *myState = (TStoreState *) self;

    Assert(myState->pub.mydest == DestTuplestore);
    myState->tstore = tStore;
    myState->cxt = tContext;
    myState->detoast = detoast;
}