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.
 *
 * Also optionally, we can apply a tuple conversion map before storing.
 *
 *
 * Portions Copyright (c) 1996-2024, 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/detoast.h"
#include "access/tupconvert.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? */
    TupleDesc   target_tupdesc; /* target tupdesc, or NULL if none */
    const char *map_failure_msg;    /* tupdesc mapping failure message */
    /* workspace: */
    Datum      *outvalues;      /* values array for result tuple */
    Datum      *tofree;         /* temp values to be pfree'd */
    TupleConversionMap *tupmap; /* conversion map, if needed */
    TupleTableSlot *mapslot;    /* slot for mapped tuples */
} TStoreState;
 
 
static bool tstoreReceiveSlot_notoast(TupleTableSlot *slot, DestReceiver *self);
static bool tstoreReceiveSlot_detoast(TupleTableSlot *slot, DestReceiver *self);
static bool tstoreReceiveSlot_tupmap(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;
    int         natts = typeinfo->natts;
    int         i;
 
    /* Check if any columns require detoast work */
    if (myState->detoast)
    {
        for (i = 0; i < natts; i++)
        {
            Form_pg_attribute attr = TupleDescAttr(typeinfo, i);
 
            if (attr->attisdropped)
                continue;
            if (attr->attlen == -1)
            {
                needtoast = true;
                break;
            }
        }
    }
 
    /* Check if tuple conversion is needed */
    if (myState->target_tupdesc)
        myState->tupmap = convert_tuples_by_position(typeinfo,
                                                     myState->target_tupdesc,
                                                     myState->map_failure_msg);
    else
        myState->tupmap = NULL;
 
    /* Set up appropriate callback */
    if (needtoast)
    {
        Assert(!myState->tupmap);
        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));
        myState->mapslot = NULL;
    }
    else if (myState->tupmap)
    {
        myState->pub.receiveSlot = tstoreReceiveSlot_tupmap;
        myState->outvalues = NULL;
        myState->tofree = NULL;
        myState->mapslot = MakeSingleTupleTableSlot(myState->target_tupdesc,
                                                    &TTSOpsVirtual);
    }
    else
    {
        myState->pub.receiveSlot = tstoreReceiveSlot_notoast;
        myState->outvalues = NULL;
        myState->tofree = NULL;
        myState->mapslot = 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 nor map anything.
 */
static bool
tstoreReceiveSlot_notoast(TupleTableSlot *slot, DestReceiver *self)
{
    TStoreState *myState = (TStoreState *) self;
 
    tuplestore_puttupleslot(myState->tstore, slot);
 
    return true;
}
 
/*
 * 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 bool
tstoreReceiveSlot_detoast(TupleTableSlot *slot, DestReceiver *self)
{
    TStoreState *myState = (TStoreState *) self;
    TupleDesc   typeinfo = slot->tts_tupleDescriptor;
    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];
        Form_pg_attribute attr = TupleDescAttr(typeinfo, i);
 
        if (!attr->attisdropped && attr->attlen == -1 && !slot->tts_isnull[i])
        {
            if (VARATT_IS_EXTERNAL(DatumGetPointer(val)))
            {
                val = PointerGetDatum(detoast_external_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]));
 
    return true;
}
 
/*
 * Receive a tuple from the executor and store it in the tuplestore.
 * This is for the case where we must apply a tuple conversion map.
 */
static bool
tstoreReceiveSlot_tupmap(TupleTableSlot *slot, DestReceiver *self)
{
    TStoreState *myState = (TStoreState *) self;
 
    execute_attr_map_slot(myState->tupmap->attrMap, slot, myState->mapslot);
    tuplestore_puttupleslot(myState->tstore, myState->mapslot);
 
    return true;
}
 
/*
 * 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;
    if (myState->tupmap)
        free_conversion_map(myState->tupmap);
    myState->tupmap = NULL;
    if (myState->mapslot)
        ExecDropSingleTupleTableSlot(myState->mapslot);
    myState->mapslot = 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
 *
 * tStore: where to store the tuples
 * tContext: memory context containing tStore
 * detoast: forcibly detoast contained data?
 * target_tupdesc: if not NULL, forcibly convert tuples to this rowtype
 * map_failure_msg: error message to use if mapping to target_tupdesc fails
 *
 * We don't currently support both detoast and target_tupdesc at the same
 * time, just because no existing caller needs that combination.
 */
void
SetTuplestoreDestReceiverParams(DestReceiver *self,
                                Tuplestorestate *tStore,
                                MemoryContext tContext,
                                bool detoast,
                                TupleDesc target_tupdesc,
                                const char *map_failure_msg)
{
    TStoreState *myState = (TStoreState *) self;
 
    Assert(!(detoast && target_tupdesc));
 
    Assert(myState->pub.mydest == DestTuplestore);
    myState->tstore = tStore;
    myState->cxt = tContext;
    myState->detoast = detoast;
    myState->target_tupdesc = target_tupdesc;
    myState->map_failure_msg = map_failure_msg;
}