execJunk.c

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/*-------------------------------------------------------------------------
 *
 * execJunk.c
 *    Junk attribute support stuff....
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/execJunk.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "executor/executor.h"

/*-------------------------------------------------------------------------
 *      XXX this stuff should be rewritten to take advantage
 *          of ExecProject() and the ProjectionInfo node.
 *          -cim 6/3/91
 *
 * An attribute of a tuple living inside the executor, can be
 * either a normal attribute or a "junk" attribute. "junk" attributes
 * never make it out of the executor, i.e. they are never printed,
 * returned or stored on disk. Their only purpose in life is to
 * store some information useful only to the executor, mainly the values
 * of system attributes like "ctid", or sort key columns that are not to
 * be output.
 *
 * The general idea is the following: A target list consists of a list of
 * TargetEntry nodes containing expressions. Each TargetEntry has a field
 * called 'resjunk'. If the value of this field is true then the
 * corresponding attribute is a "junk" attribute.
 *
 * When we initialize a plan we call ExecInitJunkFilter to create a filter.
 *
 * We then execute the plan, treating the resjunk attributes like any others.
 *
 * Finally, when at the top level we get back a tuple, we can call
 * ExecFindJunkAttribute/ExecGetJunkAttribute to retrieve the values of the
 * junk attributes we are interested in, and ExecFilterJunk to remove all the
 * junk attributes from a tuple.  This new "clean" tuple is then printed,
 * inserted, or updated.
 *
 *-------------------------------------------------------------------------
 */

/*
 * ExecInitJunkFilter
 *
 * Initialize the Junk filter.
 *
 * The source targetlist is passed in.  The output tuple descriptor is
 * built from the non-junk tlist entries, plus the passed specification
 * of whether to include room for an OID or not.
 * An optional resultSlot can be passed as well.
 */
JunkFilter *
ExecInitJunkFilter(List *targetList, bool hasoid, TupleTableSlot *slot)
{
    JunkFilter *junkfilter;
    TupleDesc   cleanTupType;
    int         cleanLength;
    AttrNumber *cleanMap;
    ListCell   *t;
    AttrNumber  cleanResno;

    /*
     * Compute the tuple descriptor for the cleaned tuple.
     */
    cleanTupType = ExecCleanTypeFromTL(targetList, hasoid);

    /*
     * Use the given slot, or make a new slot if we weren't given one.
     */
    if (slot)
        ExecSetSlotDescriptor(slot, cleanTupType);
    else
        slot = MakeSingleTupleTableSlot(cleanTupType);

    /*
     * Now calculate the mapping between the original tuple's attributes and
     * the "clean" tuple's attributes.
     *
     * The "map" is an array of "cleanLength" attribute numbers, i.e. one
     * entry for every attribute of the "clean" tuple. The value of this entry
     * is the attribute number of the corresponding attribute of the
     * "original" tuple.  (Zero indicates a NULL output attribute, but we do
     * not use that feature in this routine.)
     */
    cleanLength = cleanTupType->natts;
    if (cleanLength > 0)
    {
        cleanMap = (AttrNumber *) palloc(cleanLength * sizeof(AttrNumber));
        cleanResno = 1;
        foreach(t, targetList)
        {
            TargetEntry *tle = lfirst(t);

            if (!tle->resjunk)
            {
                cleanMap[cleanResno - 1] = tle->resno;
                cleanResno++;
            }
        }
    }
    else
        cleanMap = NULL;

    /*
     * Finally create and initialize the JunkFilter struct.
     */
    junkfilter = makeNode(JunkFilter);

    junkfilter->jf_targetList = targetList;
    junkfilter->jf_cleanTupType = cleanTupType;
    junkfilter->jf_cleanMap = cleanMap;
    junkfilter->jf_resultSlot = slot;

    return junkfilter;
}

/*
 * ExecInitJunkFilterConversion
 *
 * Initialize a JunkFilter for rowtype conversions.
 *
 * Here, we are given the target "clean" tuple descriptor rather than
 * inferring it from the targetlist.  The target descriptor can contain
 * deleted columns.  It is assumed that the caller has checked that the
 * non-deleted columns match up with the non-junk columns of the targetlist.
 */
JunkFilter *
ExecInitJunkFilterConversion(List *targetList,
                             TupleDesc cleanTupType,
                             TupleTableSlot *slot)
{
    JunkFilter *junkfilter;
    int         cleanLength;
    AttrNumber *cleanMap;
    ListCell   *t;
    int         i;

    /*
     * Use the given slot, or make a new slot if we weren't given one.
     */
    if (slot)
        ExecSetSlotDescriptor(slot, cleanTupType);
    else
        slot = MakeSingleTupleTableSlot(cleanTupType);

    /*
     * Calculate the mapping between the original tuple's attributes and the
     * "clean" tuple's attributes.
     *
     * The "map" is an array of "cleanLength" attribute numbers, i.e. one
     * entry for every attribute of the "clean" tuple. The value of this entry
     * is the attribute number of the corresponding attribute of the
     * "original" tuple.  We store zero for any deleted attributes, marking
     * that a NULL is needed in the output tuple.
     */
    cleanLength = cleanTupType->natts;
    if (cleanLength > 0)
    {
        cleanMap = (AttrNumber *) palloc0(cleanLength * sizeof(AttrNumber));
        t = list_head(targetList);
        for (i = 0; i < cleanLength; i++)
        {
            if (cleanTupType->attrs[i]->attisdropped)
                continue;       /* map entry is already zero */
            for (;;)
            {
                TargetEntry *tle = lfirst(t);

                t = lnext(t);
                if (!tle->resjunk)
                {
                    cleanMap[i] = tle->resno;
                    break;
                }
            }
        }
    }
    else
        cleanMap = NULL;

    /*
     * Finally create and initialize the JunkFilter struct.
     */
    junkfilter = makeNode(JunkFilter);

    junkfilter->jf_targetList = targetList;
    junkfilter->jf_cleanTupType = cleanTupType;
    junkfilter->jf_cleanMap = cleanMap;
    junkfilter->jf_resultSlot = slot;

    return junkfilter;
}

/*
 * ExecFindJunkAttribute
 *
 * Locate the specified junk attribute in the junk filter's targetlist,
 * and return its resno.  Returns InvalidAttrNumber if not found.
 */
AttrNumber
ExecFindJunkAttribute(JunkFilter *junkfilter, const char *attrName)
{
    return ExecFindJunkAttributeInTlist(junkfilter->jf_targetList, attrName);
}

/*
 * ExecFindJunkAttributeInTlist
 *
 * Find a junk attribute given a subplan's targetlist (not necessarily
 * part of a JunkFilter).
 */
AttrNumber
ExecFindJunkAttributeInTlist(List *targetlist, const char *attrName)
{
    ListCell   *t;

    foreach(t, targetlist)
    {
        TargetEntry *tle = lfirst(t);

        if (tle->resjunk && tle->resname &&
            (strcmp(tle->resname, attrName) == 0))
        {
            /* We found it ! */
            return tle->resno;
        }
    }

    return InvalidAttrNumber;
}

/*
 * ExecGetJunkAttribute
 *
 * Given a junk filter's input tuple (slot) and a junk attribute's number
 * previously found by ExecFindJunkAttribute, extract & return the value and
 * isNull flag of the attribute.
 */
Datum
ExecGetJunkAttribute(TupleTableSlot *slot, AttrNumber attno,
                     bool *isNull)
{
    Assert(attno > 0);

    return slot_getattr(slot, attno, isNull);
}

/*
 * ExecFilterJunk
 *
 * Construct and return a slot with all the junk attributes removed.
 */
TupleTableSlot *
ExecFilterJunk(JunkFilter *junkfilter, TupleTableSlot *slot)
{
    TupleTableSlot *resultSlot;
    AttrNumber *cleanMap;
    TupleDesc   cleanTupType;
    int         cleanLength;
    int         i;
    Datum      *values;
    bool       *isnull;
    Datum      *old_values;
    bool       *old_isnull;

    /*
     * Extract all the values of the old tuple.
     */
    slot_getallattrs(slot);
    old_values = slot->tts_values;
    old_isnull = slot->tts_isnull;

    /*
     * get info from the junk filter
     */
    cleanTupType = junkfilter->jf_cleanTupType;
    cleanLength = cleanTupType->natts;
    cleanMap = junkfilter->jf_cleanMap;
    resultSlot = junkfilter->jf_resultSlot;

    /*
     * Prepare to build a virtual result tuple.
     */
    ExecClearTuple(resultSlot);
    values = resultSlot->tts_values;
    isnull = resultSlot->tts_isnull;

    /*
     * Transpose data into proper fields of the new tuple.
     */
    for (i = 0; i < cleanLength; i++)
    {
        int         j = cleanMap[i];

        if (j == 0)
        {
            values[i] = (Datum) 0;
            isnull[i] = true;
        }
        else
        {
            values[i] = old_values[j - 1];
            isnull[i] = old_isnull[j - 1];
        }
    }

    /*
     * And return the virtual tuple.
     */
    return ExecStoreVirtualTuple(resultSlot);
}