nodeMergejoin.c

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/*-------------------------------------------------------------------------
 *
 * nodeMergejoin.c
 *    routines supporting merge joins
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeMergejoin.c
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 *      ExecMergeJoin           mergejoin outer and inner relations.
 *      ExecInitMergeJoin       creates and initializes run time states
 *      ExecEndMergeJoin        cleans up the node.
 *
 * NOTES
 *
 *      Merge-join is done by joining the inner and outer tuples satisfying
 *      join clauses of the form ((= outerKey innerKey) ...).
 *      The join clause list is provided by the query planner and may contain
 *      more than one (= outerKey innerKey) clause (for composite sort key).
 *
 *      However, the query executor needs to know whether an outer
 *      tuple is "greater/smaller" than an inner tuple so that it can
 *      "synchronize" the two relations. For example, consider the following
 *      relations:
 *
 *              outer: (0 ^1 1 2 5 5 5 6 6 7)   current tuple: 1
 *              inner: (1 ^3 5 5 5 5 6)         current tuple: 3
 *
 *      To continue the merge-join, the executor needs to scan both inner
 *      and outer relations till the matching tuples 5. It needs to know
 *      that currently inner tuple 3 is "greater" than outer tuple 1 and
 *      therefore it should scan the outer relation first to find a
 *      matching tuple and so on.
 *
 *      Therefore, rather than directly executing the merge join clauses,
 *      we evaluate the left and right key expressions separately and then
 *      compare the columns one at a time (see MJCompare).  The planner
 *      passes us enough information about the sort ordering of the inputs
 *      to allow us to determine how to make the comparison.  We may use the
 *      appropriate btree comparison function, since Postgres' only notion
 *      of ordering is specified by btree opfamilies.
 *
 *
 *      Consider the above relations and suppose that the executor has
 *      just joined the first outer "5" with the last inner "5". The
 *      next step is of course to join the second outer "5" with all
 *      the inner "5's". This requires repositioning the inner "cursor"
 *      to point at the first inner "5". This is done by "marking" the
 *      first inner 5 so we can restore the "cursor" to it before joining
 *      with the second outer 5. The access method interface provides
 *      routines to mark and restore to a tuple.
 *
 *
 *      Essential operation of the merge join algorithm is as follows:
 *
 *      Join {
 *          get initial outer and inner tuples              INITIALIZE
 *          do forever {
 *              while (outer != inner) {                    SKIP_TEST
 *                  if (outer < inner)
 *                      advance outer                       SKIPOUTER_ADVANCE
 *                  else
 *                      advance inner                       SKIPINNER_ADVANCE
 *              }
 *              mark inner position                         SKIP_TEST
 *              do forever {
 *                  while (outer == inner) {
 *                      join tuples                         JOINTUPLES
 *                      advance inner position              NEXTINNER
 *                  }
 *                  advance outer position                  NEXTOUTER
 *                  if (outer == mark)                      TESTOUTER
 *                      restore inner position to mark      TESTOUTER
 *                  else
 *                      break   // return to top of outer loop
 *              }
 *          }
 *      }
 *
 *      The merge join operation is coded in the fashion
 *      of a state machine.  At each state, we do something and then
 *      proceed to another state.  This state is stored in the node's
 *      execution state information and is preserved across calls to
 *      ExecMergeJoin. -cim 10/31/89
 */
#include "postgres.h"
 
#include "access/nbtree.h"
#include "executor/execdebug.h"
#include "executor/nodeMergejoin.h"
#include "miscadmin.h"
#include "utils/lsyscache.h"
 
 
/*
 * States of the ExecMergeJoin state machine
 */
#define EXEC_MJ_INITIALIZE_OUTER        1
#define EXEC_MJ_INITIALIZE_INNER        2
#define EXEC_MJ_JOINTUPLES              3
#define EXEC_MJ_NEXTOUTER               4
#define EXEC_MJ_TESTOUTER               5
#define EXEC_MJ_NEXTINNER               6
#define EXEC_MJ_SKIP_TEST               7
#define EXEC_MJ_SKIPOUTER_ADVANCE       8
#define EXEC_MJ_SKIPINNER_ADVANCE       9
#define EXEC_MJ_ENDOUTER                10
#define EXEC_MJ_ENDINNER                11
 
/*
 * Runtime data for each mergejoin clause
 */
typedef struct MergeJoinClauseData
{
    /* Executable expression trees */
    ExprState  *lexpr;          /* left-hand (outer) input expression */
    ExprState  *rexpr;          /* right-hand (inner) input expression */
 
    /*
     * If we have a current left or right input tuple, the values of the
     * expressions are loaded into these fields:
     */
    Datum       ldatum;         /* current left-hand value */
    Datum       rdatum;         /* current right-hand value */
    bool        lisnull;        /* and their isnull flags */
    bool        risnull;
 
    /*
     * Everything we need to know to compare the left and right values is
     * stored here.
     */
    SortSupportData ssup;
}           MergeJoinClauseData;
 
/* Result type for MJEvalOuterValues and MJEvalInnerValues */
typedef enum
{
    MJEVAL_MATCHABLE,           /* normal, potentially matchable tuple */
    MJEVAL_NONMATCHABLE,        /* tuple cannot join because it has a null */
    MJEVAL_ENDOFJOIN,           /* end of input (physical or effective) */
} MJEvalResult;
 
 
#define MarkInnerTuple(innerTupleSlot, mergestate) \
    ExecCopySlot((mergestate)->mj_MarkedTupleSlot, (innerTupleSlot))
 
 
/*
 * MJExamineQuals
 *
 * This deconstructs the list of mergejoinable expressions, which is given
 * to us by the planner in the form of a list of "leftexpr = rightexpr"
 * expression trees in the order matching the sort columns of the inputs.
 * We build an array of MergeJoinClause structs containing the information
 * we will need at runtime.  Each struct essentially tells us how to compare
 * the two expressions from the original clause.
 *
 * In addition to the expressions themselves, the planner passes the btree
 * opfamily OID, collation OID, btree strategy number (BTLessStrategyNumber or
 * BTGreaterStrategyNumber), and nulls-first flag that identify the intended
 * sort ordering for each merge key.  The mergejoinable operator is an
 * equality operator in the opfamily, and the two inputs are guaranteed to be
 * ordered in either increasing or decreasing (respectively) order according
 * to the opfamily and collation, with nulls at the indicated end of the range.
 * This allows us to obtain the needed comparison function from the opfamily.
 */
static MergeJoinClause
MJExamineQuals(List *mergeclauses,
               Oid *mergefamilies,
               Oid *mergecollations,
               int *mergestrategies,
               bool *mergenullsfirst,
               PlanState *parent)
{
    MergeJoinClause clauses;
    int         nClauses = list_length(mergeclauses);
    int         iClause;
    ListCell   *cl;
 
    clauses = (MergeJoinClause) palloc0(nClauses * sizeof(MergeJoinClauseData));
 
    iClause = 0;
    foreach(cl, mergeclauses)
    {
        OpExpr     *qual = (OpExpr *) lfirst(cl);
        MergeJoinClause clause = &clauses[iClause];
        Oid         opfamily = mergefamilies[iClause];
        Oid         collation = mergecollations[iClause];
        StrategyNumber opstrategy = mergestrategies[iClause];
        bool        nulls_first = mergenullsfirst[iClause];
        int         op_strategy;
        Oid         op_lefttype;
        Oid         op_righttype;
        Oid         sortfunc;
 
        if (!IsA(qual, OpExpr))
            elog(ERROR, "mergejoin clause is not an OpExpr");
 
        /*
         * Prepare the input expressions for execution.
         */
        clause->lexpr = ExecInitExpr((Expr *) linitial(qual->args), parent);
        clause->rexpr = ExecInitExpr((Expr *) lsecond(qual->args), parent);
 
        /* Set up sort support data */
        clause->ssup.ssup_cxt = CurrentMemoryContext;
        clause->ssup.ssup_collation = collation;
        if (opstrategy == BTLessStrategyNumber)
            clause->ssup.ssup_reverse = false;
        else if (opstrategy == BTGreaterStrategyNumber)
            clause->ssup.ssup_reverse = true;
        else                    /* planner screwed up */
            elog(ERROR, "unsupported mergejoin strategy %d", opstrategy);
        clause->ssup.ssup_nulls_first = nulls_first;
 
        /* Extract the operator's declared left/right datatypes */
        get_op_opfamily_properties(qual->opno, opfamily, false,
                                   &op_strategy,
                                   &op_lefttype,
                                   &op_righttype);
        if (op_strategy != BTEqualStrategyNumber)   /* should not happen */
            elog(ERROR, "cannot merge using non-equality operator %u",
                 qual->opno);
 
        /*
         * sortsupport routine must know if abbreviation optimization is
         * applicable in principle.  It is never applicable for merge joins
         * because there is no convenient opportunity to convert to
         * alternative representation.
         */
        clause->ssup.abbreviate = false;
 
        /* And get the matching support or comparison function */
        Assert(clause->ssup.comparator == NULL);
        sortfunc = get_opfamily_proc(opfamily,
                                     op_lefttype,
                                     op_righttype,
                                     BTSORTSUPPORT_PROC);
        if (OidIsValid(sortfunc))
        {
            /* The sort support function can provide a comparator */
            OidFunctionCall1(sortfunc, PointerGetDatum(&clause->ssup));
        }
        if (clause->ssup.comparator == NULL)
        {
            /* support not available, get comparison func */
            sortfunc = get_opfamily_proc(opfamily,
                                         op_lefttype,
                                         op_righttype,
                                         BTORDER_PROC);
            if (!OidIsValid(sortfunc))  /* should not happen */
                elog(ERROR, "missing support function %d(%u,%u) in opfamily %u",
                     BTORDER_PROC, op_lefttype, op_righttype, opfamily);
            /* We'll use a shim to call the old-style btree comparator */
            PrepareSortSupportComparisonShim(sortfunc, &clause->ssup);
        }
 
        iClause++;
    }
 
    return clauses;
}
 
/*
 * MJEvalOuterValues
 *
 * Compute the values of the mergejoined expressions for the current
 * outer tuple.  We also detect whether it's impossible for the current
 * outer tuple to match anything --- this is true if it yields a NULL
 * input, since we assume mergejoin operators are strict.  If the NULL
 * is in the first join column, and that column sorts nulls last, then
 * we can further conclude that no following tuple can match anything
 * either, since they must all have nulls in the first column.  However,
 * that case is only interesting if we're not in FillOuter mode, else
 * we have to visit all the tuples anyway.
 *
 * For the convenience of callers, we also make this routine responsible
 * for testing for end-of-input (null outer tuple), and returning
 * MJEVAL_ENDOFJOIN when that's seen.  This allows the same code to be used
 * for both real end-of-input and the effective end-of-input represented by
 * a first-column NULL.
 *
 * We evaluate the values in OuterEContext, which can be reset each
 * time we move to a new tuple.
 */
static MJEvalResult
MJEvalOuterValues(MergeJoinState *mergestate)
{
    ExprContext *econtext = mergestate->mj_OuterEContext;
    MJEvalResult result = MJEVAL_MATCHABLE;
    int         i;
    MemoryContext oldContext;
 
    /* Check for end of outer subplan */
    if (TupIsNull(mergestate->mj_OuterTupleSlot))
        return MJEVAL_ENDOFJOIN;
 
    ResetExprContext(econtext);
 
    oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
 
    econtext->ecxt_outertuple = mergestate->mj_OuterTupleSlot;
 
    for (i = 0; i < mergestate->mj_NumClauses; i++)
    {
        MergeJoinClause clause = &mergestate->mj_Clauses[i];
 
        clause->ldatum = ExecEvalExpr(clause->lexpr, econtext,
                                      &clause->lisnull);
        if (clause->lisnull)
        {
            /* match is impossible; can we end the join early? */
            if (i == 0 && !clause->ssup.ssup_nulls_first &&
                !mergestate->mj_FillOuter)
                result = MJEVAL_ENDOFJOIN;
            else if (result == MJEVAL_MATCHABLE)
                result = MJEVAL_NONMATCHABLE;
        }
    }
 
    MemoryContextSwitchTo(oldContext);
 
    return result;
}
 
/*
 * MJEvalInnerValues
 *
 * Same as above, but for the inner tuple.  Here, we have to be prepared
 * to load data from either the true current inner, or the marked inner,
 * so caller must tell us which slot to load from.
 */
static MJEvalResult
MJEvalInnerValues(MergeJoinState *mergestate, TupleTableSlot *innerslot)
{
    ExprContext *econtext = mergestate->mj_InnerEContext;
    MJEvalResult result = MJEVAL_MATCHABLE;
    int         i;
    MemoryContext oldContext;
 
    /* Check for end of inner subplan */
    if (TupIsNull(innerslot))
        return MJEVAL_ENDOFJOIN;
 
    ResetExprContext(econtext);
 
    oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
 
    econtext->ecxt_innertuple = innerslot;
 
    for (i = 0; i < mergestate->mj_NumClauses; i++)
    {
        MergeJoinClause clause = &mergestate->mj_Clauses[i];
 
        clause->rdatum = ExecEvalExpr(clause->rexpr, econtext,
                                      &clause->risnull);
        if (clause->risnull)
        {
            /* match is impossible; can we end the join early? */
            if (i == 0 && !clause->ssup.ssup_nulls_first &&
                !mergestate->mj_FillInner)
                result = MJEVAL_ENDOFJOIN;
            else if (result == MJEVAL_MATCHABLE)
                result = MJEVAL_NONMATCHABLE;
        }
    }
 
    MemoryContextSwitchTo(oldContext);
 
    return result;
}
 
/*
 * MJCompare
 *
 * Compare the mergejoinable values of the current two input tuples
 * and return 0 if they are equal (ie, the mergejoin equalities all
 * succeed), >0 if outer > inner, <0 if outer < inner.
 *
 * MJEvalOuterValues and MJEvalInnerValues must already have been called
 * for the current outer and inner tuples, respectively.
 */
static int
MJCompare(MergeJoinState *mergestate)
{
    int         result = 0;
    bool        nulleqnull = false;
    ExprContext *econtext = mergestate->js.ps.ps_ExprContext;
    int         i;
    MemoryContext oldContext;
 
    /*
     * Call the comparison functions in short-lived context, in case they leak
     * memory.
     */
    ResetExprContext(econtext);
 
    oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
 
    for (i = 0; i < mergestate->mj_NumClauses; i++)
    {
        MergeJoinClause clause = &mergestate->mj_Clauses[i];
 
        /*
         * Special case for NULL-vs-NULL, else use standard comparison.
         */
        if (clause->lisnull && clause->risnull)
        {
            nulleqnull = true;  /* NULL "=" NULL */
            continue;
        }
 
        result = ApplySortComparator(clause->ldatum, clause->lisnull,
                                     clause->rdatum, clause->risnull,
                                     &clause->ssup);
 
        if (result != 0)
            break;
    }
 
    /*
     * If we had any NULL-vs-NULL inputs, we do not want to report that the
     * tuples are equal.  Instead, if result is still 0, change it to +1. This
     * will result in advancing the inner side of the join.
     *
     * Likewise, if there was a constant-false joinqual, do not report
     * equality.  We have to check this as part of the mergequals, else the
     * rescan logic will do the wrong thing.
     */
    if (result == 0 &&
        (nulleqnull || mergestate->mj_ConstFalseJoin))
        result = 1;
 
    MemoryContextSwitchTo(oldContext);
 
    return result;
}
 
 
/*
 * Generate a fake join tuple with nulls for the inner tuple,
 * and return it if it passes the non-join quals.
 */
static TupleTableSlot *
MJFillOuter(MergeJoinState *node)
{
    ExprContext *econtext = node->js.ps.ps_ExprContext;
    ExprState  *otherqual = node->js.ps.qual;
 
    ResetExprContext(econtext);
 
    econtext->ecxt_outertuple = node->mj_OuterTupleSlot;
    econtext->ecxt_innertuple = node->mj_NullInnerTupleSlot;
 
    if (ExecQual(otherqual, econtext))
    {
        /*
         * qualification succeeded.  now form the desired projection tuple and
         * return the slot containing it.
         */
        MJ_printf("ExecMergeJoin: returning outer fill tuple\n");
 
        return ExecProject(node->js.ps.ps_ProjInfo);
    }
    else
        InstrCountFiltered2(node, 1);
 
    return NULL;
}
 
/*
 * Generate a fake join tuple with nulls for the outer tuple,
 * and return it if it passes the non-join quals.
 */
static TupleTableSlot *
MJFillInner(MergeJoinState *node)
{
    ExprContext *econtext = node->js.ps.ps_ExprContext;
    ExprState  *otherqual = node->js.ps.qual;
 
    ResetExprContext(econtext);
 
    econtext->ecxt_outertuple = node->mj_NullOuterTupleSlot;
    econtext->ecxt_innertuple = node->mj_InnerTupleSlot;
 
    if (ExecQual(otherqual, econtext))
    {
        /*
         * qualification succeeded.  now form the desired projection tuple and
         * return the slot containing it.
         */
        MJ_printf("ExecMergeJoin: returning inner fill tuple\n");
 
        return ExecProject(node->js.ps.ps_ProjInfo);
    }
    else
        InstrCountFiltered2(node, 1);
 
    return NULL;
}
 
 
/*
 * Check that a qual condition is constant true or constant false.
 * If it is constant false (or null), set *is_const_false to true.
 *
 * Constant true would normally be represented by a NIL list, but we allow an
 * actual bool Const as well.  We do expect that the planner will have thrown
 * away any non-constant terms that have been ANDed with a constant false.
 */
static bool
check_constant_qual(List *qual, bool *is_const_false)
{
    ListCell   *lc;
 
    foreach(lc, qual)
    {
        Const      *con = (Const *) lfirst(lc);
 
        if (!con || !IsA(con, Const))
            return false;
        if (con->constisnull || !DatumGetBool(con->constvalue))
            *is_const_false = true;
    }
    return true;
}
 
 
/* ----------------------------------------------------------------
 *      ExecMergeTupleDump
 *
 *      This function is called through the MJ_dump() macro
 *      when EXEC_MERGEJOINDEBUG is defined
 * ----------------------------------------------------------------
 */
#ifdef EXEC_MERGEJOINDEBUG
 
static void
ExecMergeTupleDumpOuter(MergeJoinState *mergestate)
{
    TupleTableSlot *outerSlot = mergestate->mj_OuterTupleSlot;
 
    printf("==== outer tuple ====\n");
    if (TupIsNull(outerSlot))
        printf("(nil)\n");
    else
        MJ_debugtup(outerSlot);
}
 
static void
ExecMergeTupleDumpInner(MergeJoinState *mergestate)
{
    TupleTableSlot *innerSlot = mergestate->mj_InnerTupleSlot;
 
    printf("==== inner tuple ====\n");
    if (TupIsNull(innerSlot))
        printf("(nil)\n");
    else
        MJ_debugtup(innerSlot);
}
 
static void
ExecMergeTupleDumpMarked(MergeJoinState *mergestate)
{
    TupleTableSlot *markedSlot = mergestate->mj_MarkedTupleSlot;
 
    printf("==== marked tuple ====\n");
    if (TupIsNull(markedSlot))
        printf("(nil)\n");
    else
        MJ_debugtup(markedSlot);
}
 
static void
ExecMergeTupleDump(MergeJoinState *mergestate)
{
    printf("******** ExecMergeTupleDump ********\n");
 
    ExecMergeTupleDumpOuter(mergestate);
    ExecMergeTupleDumpInner(mergestate);
    ExecMergeTupleDumpMarked(mergestate);
 
    printf("********\n");
}
#endif
 
/* ----------------------------------------------------------------
 *      ExecMergeJoin
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecMergeJoin(PlanState *pstate)
{
    MergeJoinState *node = castNode(MergeJoinState, pstate);
    ExprState  *joinqual;
    ExprState  *otherqual;
    bool        qualResult;
    int         compareResult;
    PlanState  *innerPlan;
    TupleTableSlot *innerTupleSlot;
    PlanState  *outerPlan;
    TupleTableSlot *outerTupleSlot;
    ExprContext *econtext;
    bool        doFillOuter;
    bool        doFillInner;
 
    CHECK_FOR_INTERRUPTS();
 
    /*
     * get information from node
     */
    innerPlan = innerPlanState(node);
    outerPlan = outerPlanState(node);
    econtext = node->js.ps.ps_ExprContext;
    joinqual = node->js.joinqual;
    otherqual = node->js.ps.qual;
    doFillOuter = node->mj_FillOuter;
    doFillInner = node->mj_FillInner;
 
    /*
     * Reset per-tuple memory context to free any expression evaluation
     * storage allocated in the previous tuple cycle.
     */
    ResetExprContext(econtext);
 
    /*
     * ok, everything is setup.. let's go to work
     */
    for (;;)
    {
        MJ_dump(node);
 
        /*
         * get the current state of the join and do things accordingly.
         */
        switch (node->mj_JoinState)
        {
                /*
                 * EXEC_MJ_INITIALIZE_OUTER means that this is the first time
                 * ExecMergeJoin() has been called and so we have to fetch the
                 * first matchable tuple for both outer and inner subplans. We
                 * do the outer side in INITIALIZE_OUTER state, then advance
                 * to INITIALIZE_INNER state for the inner subplan.
                 */
            case EXEC_MJ_INITIALIZE_OUTER:
                MJ_printf("ExecMergeJoin: EXEC_MJ_INITIALIZE_OUTER\n");
 
                outerTupleSlot = ExecProcNode(outerPlan);
                node->mj_OuterTupleSlot = outerTupleSlot;
 
                /* Compute join values and check for unmatchability */
                switch (MJEvalOuterValues(node))
                {
                    case MJEVAL_MATCHABLE:
                        /* OK to go get the first inner tuple */
                        node->mj_JoinState = EXEC_MJ_INITIALIZE_INNER;
                        break;
                    case MJEVAL_NONMATCHABLE:
                        /* Stay in same state to fetch next outer tuple */
                        if (doFillOuter)
                        {
                            /*
                             * Generate a fake join tuple with nulls for the
                             * inner tuple, and return it if it passes the
                             * non-join quals.
                             */
                            TupleTableSlot *result;
 
                            result = MJFillOuter(node);
                            if (result)
                                return result;
                        }
                        break;
                    case MJEVAL_ENDOFJOIN:
                        /* No more outer tuples */
                        MJ_printf("ExecMergeJoin: nothing in outer subplan\n");
                        if (doFillInner)
                        {
                            /*
                             * Need to emit right-join tuples for remaining
                             * inner tuples. We set MatchedInner = true to
                             * force the ENDOUTER state to advance inner.
                             */
                            node->mj_JoinState = EXEC_MJ_ENDOUTER;
                            node->mj_MatchedInner = true;
                            break;
                        }
                        /* Otherwise we're done. */
                        return NULL;
                }
                break;
 
            case EXEC_MJ_INITIALIZE_INNER:
                MJ_printf("ExecMergeJoin: EXEC_MJ_INITIALIZE_INNER\n");
 
                innerTupleSlot = ExecProcNode(innerPlan);
                node->mj_InnerTupleSlot = innerTupleSlot;
 
                /* Compute join values and check for unmatchability */
                switch (MJEvalInnerValues(node, innerTupleSlot))
                {
                    case MJEVAL_MATCHABLE:
 
                        /*
                         * OK, we have the initial tuples.  Begin by skipping
                         * non-matching tuples.
                         */
                        node->mj_JoinState = EXEC_MJ_SKIP_TEST;
                        break;
                    case MJEVAL_NONMATCHABLE:
                        /* Mark before advancing, if wanted */
                        if (node->mj_ExtraMarks)
                            ExecMarkPos(innerPlan);
                        /* Stay in same state to fetch next inner tuple */
                        if (doFillInner)
                        {
                            /*
                             * Generate a fake join tuple with nulls for the
                             * outer tuple, and return it if it passes the
                             * non-join quals.
                             */
                            TupleTableSlot *result;
 
                            result = MJFillInner(node);
                            if (result)
                                return result;
                        }
                        break;
                    case MJEVAL_ENDOFJOIN:
                        /* No more inner tuples */
                        MJ_printf("ExecMergeJoin: nothing in inner subplan\n");
                        if (doFillOuter)
                        {
                            /*
                             * Need to emit left-join tuples for all outer
                             * tuples, including the one we just fetched.  We
                             * set MatchedOuter = false to force the ENDINNER
                             * state to emit first tuple before advancing
                             * outer.
                             */
                            node->mj_JoinState = EXEC_MJ_ENDINNER;
                            node->mj_MatchedOuter = false;
                            break;
                        }
                        /* Otherwise we're done. */
                        return NULL;
                }
                break;
 
                /*
                 * EXEC_MJ_JOINTUPLES means we have two tuples which satisfied
                 * the merge clause so we join them and then proceed to get
                 * the next inner tuple (EXEC_MJ_NEXTINNER).
                 */
            case EXEC_MJ_JOINTUPLES:
                MJ_printf("ExecMergeJoin: EXEC_MJ_JOINTUPLES\n");
 
                /*
                 * Set the next state machine state.  The right things will
                 * happen whether we return this join tuple or just fall
                 * through to continue the state machine execution.
                 */
                node->mj_JoinState = EXEC_MJ_NEXTINNER;
 
                /*
                 * Check the extra qual conditions to see if we actually want
                 * to return this join tuple.  If not, can proceed with merge.
                 * We must distinguish the additional joinquals (which must
                 * pass to consider the tuples "matched" for outer-join logic)
                 * from the otherquals (which must pass before we actually
                 * return the tuple).
                 *
                 * We don't bother with a ResetExprContext here, on the
                 * assumption that we just did one while checking the merge
                 * qual.  One per tuple should be sufficient.  We do have to
                 * set up the econtext links to the tuples for ExecQual to
                 * use.
                 */
                outerTupleSlot = node->mj_OuterTupleSlot;
                econtext->ecxt_outertuple = outerTupleSlot;
                innerTupleSlot = node->mj_InnerTupleSlot;
                econtext->ecxt_innertuple = innerTupleSlot;
 
                qualResult = (joinqual == NULL ||
                              ExecQual(joinqual, econtext));
                MJ_DEBUG_QUAL(joinqual, qualResult);
 
                if (qualResult)
                {
                    node->mj_MatchedOuter = true;
                    node->mj_MatchedInner = true;
 
                    /* In an antijoin, we never return a matched tuple */
                    if (node->js.jointype == JOIN_ANTI)
                    {
                        node->mj_JoinState = EXEC_MJ_NEXTOUTER;
                        break;
                    }
 
                    /*
                     * If we only need to consider the first matching inner
                     * tuple, then advance to next outer tuple after we've
                     * processed this one.
                     */
                    if (node->js.single_match)
                        node->mj_JoinState = EXEC_MJ_NEXTOUTER;
 
                    /*
                     * In a right-antijoin, we never return a matched tuple.
                     * If it's not an inner_unique join, we need to stay on
                     * the current outer tuple to continue scanning the inner
                     * side for matches.
                     */
                    if (node->js.jointype == JOIN_RIGHT_ANTI)
                        break;
 
                    qualResult = (otherqual == NULL ||
                                  ExecQual(otherqual, econtext));
                    MJ_DEBUG_QUAL(otherqual, qualResult);
 
                    if (qualResult)
                    {
                        /*
                         * qualification succeeded.  now form the desired
                         * projection tuple and return the slot containing it.
                         */
                        MJ_printf("ExecMergeJoin: returning tuple\n");
 
                        return ExecProject(node->js.ps.ps_ProjInfo);
                    }
                    else
                        InstrCountFiltered2(node, 1);
                }
                else
                    InstrCountFiltered1(node, 1);
                break;
 
                /*
                 * EXEC_MJ_NEXTINNER means advance the inner scan to the next
                 * tuple. If the tuple is not nil, we then proceed to test it
                 * against the join qualification.
                 *
                 * Before advancing, we check to see if we must emit an
                 * outer-join fill tuple for this inner tuple.
                 */
            case EXEC_MJ_NEXTINNER:
                MJ_printf("ExecMergeJoin: EXEC_MJ_NEXTINNER\n");
 
                if (doFillInner && !node->mj_MatchedInner)
                {
                    /*
                     * Generate a fake join tuple with nulls for the outer
                     * tuple, and return it if it passes the non-join quals.
                     */
                    TupleTableSlot *result;
 
                    node->mj_MatchedInner = true;   /* do it only once */
 
                    result = MJFillInner(node);
                    if (result)
                        return result;
                }
 
                /*
                 * now we get the next inner tuple, if any.  If there's none,
                 * advance to next outer tuple (which may be able to join to
                 * previously marked tuples).
                 *
                 * NB: must NOT do "extraMarks" here, since we may need to
                 * return to previously marked tuples.
                 */
                innerTupleSlot = ExecProcNode(innerPlan);
                node->mj_InnerTupleSlot = innerTupleSlot;
                MJ_DEBUG_PROC_NODE(innerTupleSlot);
                node->mj_MatchedInner = false;
 
                /* Compute join values and check for unmatchability */
                switch (MJEvalInnerValues(node, innerTupleSlot))
                {
                    case MJEVAL_MATCHABLE:
 
                        /*
                         * Test the new inner tuple to see if it matches
                         * outer.
                         *
                         * If they do match, then we join them and move on to
                         * the next inner tuple (EXEC_MJ_JOINTUPLES).
                         *
                         * If they do not match then advance to next outer
                         * tuple.
                         */
                        compareResult = MJCompare(node);
                        MJ_DEBUG_COMPARE(compareResult);
 
                        if (compareResult == 0)
                            node->mj_JoinState = EXEC_MJ_JOINTUPLES;
                        else if (compareResult < 0)
                            node->mj_JoinState = EXEC_MJ_NEXTOUTER;
                        else    /* compareResult > 0 should not happen */
                            elog(ERROR, "mergejoin input data is out of order");
                        break;
                    case MJEVAL_NONMATCHABLE:
 
                        /*
                         * It contains a NULL and hence can't match any outer
                         * tuple, so we can skip the comparison and assume the
                         * new tuple is greater than current outer.
                         */
                        node->mj_JoinState = EXEC_MJ_NEXTOUTER;
                        break;
                    case MJEVAL_ENDOFJOIN:
 
                        /*
                         * No more inner tuples.  However, this might be only
                         * effective and not physical end of inner plan, so
                         * force mj_InnerTupleSlot to null to make sure we
                         * don't fetch more inner tuples.  (We need this hack
                         * because we are not transiting to a state where the
                         * inner plan is assumed to be exhausted.)
                         */
                        node->mj_InnerTupleSlot = NULL;
                        node->mj_JoinState = EXEC_MJ_NEXTOUTER;
                        break;
                }
                break;
 
                /*-------------------------------------------
                 * EXEC_MJ_NEXTOUTER means
                 *
                 *              outer inner
                 * outer tuple -  5     5  - marked tuple
                 *                5     5
                 *                6     6  - inner tuple
                 *                7     7
                 *
                 * we know we just bumped into the
                 * first inner tuple > current outer tuple (or possibly
                 * the end of the inner stream)
                 * so get a new outer tuple and then
                 * proceed to test it against the marked tuple
                 * (EXEC_MJ_TESTOUTER)
                 *
                 * Before advancing, we check to see if we must emit an
                 * outer-join fill tuple for this outer tuple.
                 *------------------------------------------------
                 */
            case EXEC_MJ_NEXTOUTER:
                MJ_printf("ExecMergeJoin: EXEC_MJ_NEXTOUTER\n");
 
                if (doFillOuter && !node->mj_MatchedOuter)
                {
                    /*
                     * Generate a fake join tuple with nulls for the inner
                     * tuple, and return it if it passes the non-join quals.
                     */
                    TupleTableSlot *result;
 
                    node->mj_MatchedOuter = true;   /* do it only once */
 
                    result = MJFillOuter(node);
                    if (result)
                        return result;
                }
 
                /*
                 * now we get the next outer tuple, if any
                 */
                outerTupleSlot = ExecProcNode(outerPlan);
                node->mj_OuterTupleSlot = outerTupleSlot;
                MJ_DEBUG_PROC_NODE(outerTupleSlot);
                node->mj_MatchedOuter = false;
 
                /* Compute join values and check for unmatchability */
                switch (MJEvalOuterValues(node))
                {
                    case MJEVAL_MATCHABLE:
                        /* Go test the new tuple against the marked tuple */
                        node->mj_JoinState = EXEC_MJ_TESTOUTER;
                        break;
                    case MJEVAL_NONMATCHABLE:
                        /* Can't match, so fetch next outer tuple */
                        node->mj_JoinState = EXEC_MJ_NEXTOUTER;
                        break;
                    case MJEVAL_ENDOFJOIN:
                        /* No more outer tuples */
                        MJ_printf("ExecMergeJoin: end of outer subplan\n");
                        innerTupleSlot = node->mj_InnerTupleSlot;
                        if (doFillInner && !TupIsNull(innerTupleSlot))
                        {
                            /*
                             * Need to emit right-join tuples for remaining
                             * inner tuples.
                             */
                            node->mj_JoinState = EXEC_MJ_ENDOUTER;
                            break;
                        }
                        /* Otherwise we're done. */
                        return NULL;
                }
                break;
 
                /*--------------------------------------------------------
                 * EXEC_MJ_TESTOUTER If the new outer tuple and the marked
                 * tuple satisfy the merge clause then we know we have
                 * duplicates in the outer scan so we have to restore the
                 * inner scan to the marked tuple and proceed to join the
                 * new outer tuple with the inner tuples.
                 *
                 * This is the case when
                 *                        outer inner
                 *                          4     5  - marked tuple
                 *           outer tuple -  5     5
                 *       new outer tuple -  5     5
                 *                          6     8  - inner tuple
                 *                          7    12
                 *
                 *              new outer tuple == marked tuple
                 *
                 * If the outer tuple fails the test, then we are done
                 * with the marked tuples, and we have to look for a
                 * match to the current inner tuple.  So we will
                 * proceed to skip outer tuples until outer >= inner
                 * (EXEC_MJ_SKIP_TEST).
                 *
                 *      This is the case when
                 *
                 *                        outer inner
                 *                          5     5  - marked tuple
                 *           outer tuple -  5     5
                 *       new outer tuple -  6     8  - inner tuple
                 *                          7    12
                 *
                 *              new outer tuple > marked tuple
                 *
                 *---------------------------------------------------------
                 */
            case EXEC_MJ_TESTOUTER:
                MJ_printf("ExecMergeJoin: EXEC_MJ_TESTOUTER\n");
 
                /*
                 * Here we must compare the outer tuple with the marked inner
                 * tuple.  (We can ignore the result of MJEvalInnerValues,
                 * since the marked inner tuple is certainly matchable.)
                 */
                innerTupleSlot = node->mj_MarkedTupleSlot;
                (void) MJEvalInnerValues(node, innerTupleSlot);
 
                compareResult = MJCompare(node);
                MJ_DEBUG_COMPARE(compareResult);
 
                if (compareResult == 0)
                {
                    /*
                     * the merge clause matched so now we restore the inner
                     * scan position to the first mark, and go join that tuple
                     * (and any following ones) to the new outer.
                     *
                     * If we were able to determine mark and restore are not
                     * needed, then we don't have to back up; the current
                     * inner is already the first possible match.
                     *
                     * NOTE: we do not need to worry about the MatchedInner
                     * state for the rescanned inner tuples.  We know all of
                     * them will match this new outer tuple and therefore
                     * won't be emitted as fill tuples.  This works *only*
                     * because we require the extra joinquals to be constant
                     * when doing a right, right-anti or full join ---
                     * otherwise some of the rescanned tuples might fail the
                     * extra joinquals.  This obviously won't happen for a
                     * constant-true extra joinqual, while the constant-false
                     * case is handled by forcing the merge clause to never
                     * match, so we never get here.
                     */
                    if (!node->mj_SkipMarkRestore)
                    {
                        ExecRestrPos(innerPlan);
 
                        /*
                         * ExecRestrPos probably should give us back a new
                         * Slot, but since it doesn't, use the marked slot.
                         * (The previously returned mj_InnerTupleSlot cannot
                         * be assumed to hold the required tuple.)
                         */
                        node->mj_InnerTupleSlot = innerTupleSlot;
                        /* we need not do MJEvalInnerValues again */
                    }
 
                    node->mj_JoinState = EXEC_MJ_JOINTUPLES;
                }
                else if (compareResult > 0)
                {
                    /* ----------------
                     *  if the new outer tuple didn't match the marked inner
                     *  tuple then we have a case like:
                     *
                     *           outer inner
                     *             4     4  - marked tuple
                     * new outer - 5     4
                     *             6     5  - inner tuple
                     *             7
                     *
                     *  which means that all subsequent outer tuples will be
                     *  larger than our marked inner tuples.  So we need not
                     *  revisit any of the marked tuples but can proceed to
                     *  look for a match to the current inner.  If there's
                     *  no more inners, no more matches are possible.
                     * ----------------
                     */
                    innerTupleSlot = node->mj_InnerTupleSlot;
 
                    /* reload comparison data for current inner */
                    switch (MJEvalInnerValues(node, innerTupleSlot))
                    {
                        case MJEVAL_MATCHABLE:
                            /* proceed to compare it to the current outer */
                            node->mj_JoinState = EXEC_MJ_SKIP_TEST;
                            break;
                        case MJEVAL_NONMATCHABLE:
 
                            /*
                             * current inner can't possibly match any outer;
                             * better to advance the inner scan than the
                             * outer.
                             */
                            node->mj_JoinState = EXEC_MJ_SKIPINNER_ADVANCE;
                            break;
                        case MJEVAL_ENDOFJOIN:
                            /* No more inner tuples */
                            if (doFillOuter)
                            {
                                /*
                                 * Need to emit left-join tuples for remaining
                                 * outer tuples.
                                 */
                                node->mj_JoinState = EXEC_MJ_ENDINNER;
                                break;
                            }
                            /* Otherwise we're done. */
                            return NULL;
                    }
                }
                else            /* compareResult < 0 should not happen */
                    elog(ERROR, "mergejoin input data is out of order");
                break;
 
                /*----------------------------------------------------------
                 * EXEC_MJ_SKIP_TEST means compare tuples and if they do not
                 * match, skip whichever is lesser.
                 *
                 * For example:
                 *
                 *              outer inner
                 *                5     5
                 *                5     5
                 * outer tuple -  6     8  - inner tuple
                 *                7    12
                 *                8    14
                 *
                 * we have to advance the outer scan
                 * until we find the outer 8.
                 *
                 * On the other hand:
                 *
                 *              outer inner
                 *                5     5
                 *                5     5
                 * outer tuple - 12     8  - inner tuple
                 *               14    10
                 *               17    12
                 *
                 * we have to advance the inner scan
                 * until we find the inner 12.
                 *----------------------------------------------------------
                 */
            case EXEC_MJ_SKIP_TEST:
                MJ_printf("ExecMergeJoin: EXEC_MJ_SKIP_TEST\n");
 
                /*
                 * before we advance, make sure the current tuples do not
                 * satisfy the mergeclauses.  If they do, then we update the
                 * marked tuple position and go join them.
                 */
                compareResult = MJCompare(node);
                MJ_DEBUG_COMPARE(compareResult);
 
                if (compareResult == 0)
                {
                    if (!node->mj_SkipMarkRestore)
                        ExecMarkPos(innerPlan);
 
                    MarkInnerTuple(node->mj_InnerTupleSlot, node);
 
                    node->mj_JoinState = EXEC_MJ_JOINTUPLES;
                }
                else if (compareResult < 0)
                    node->mj_JoinState = EXEC_MJ_SKIPOUTER_ADVANCE;
                else
                    /* compareResult > 0 */
                    node->mj_JoinState = EXEC_MJ_SKIPINNER_ADVANCE;
                break;
 
                /*
                 * EXEC_MJ_SKIPOUTER_ADVANCE: advance over an outer tuple that
                 * is known not to join to any inner tuple.
                 *
                 * Before advancing, we check to see if we must emit an
                 * outer-join fill tuple for this outer tuple.
                 */
            case EXEC_MJ_SKIPOUTER_ADVANCE:
                MJ_printf("ExecMergeJoin: EXEC_MJ_SKIPOUTER_ADVANCE\n");
 
                if (doFillOuter && !node->mj_MatchedOuter)
                {
                    /*
                     * Generate a fake join tuple with nulls for the inner
                     * tuple, and return it if it passes the non-join quals.
                     */
                    TupleTableSlot *result;
 
                    node->mj_MatchedOuter = true;   /* do it only once */
 
                    result = MJFillOuter(node);
                    if (result)
                        return result;
                }
 
                /*
                 * now we get the next outer tuple, if any
                 */
                outerTupleSlot = ExecProcNode(outerPlan);
                node->mj_OuterTupleSlot = outerTupleSlot;
                MJ_DEBUG_PROC_NODE(outerTupleSlot);
                node->mj_MatchedOuter = false;
 
                /* Compute join values and check for unmatchability */
                switch (MJEvalOuterValues(node))
                {
                    case MJEVAL_MATCHABLE:
                        /* Go test the new tuple against the current inner */
                        node->mj_JoinState = EXEC_MJ_SKIP_TEST;
                        break;
                    case MJEVAL_NONMATCHABLE:
                        /* Can't match, so fetch next outer tuple */
                        node->mj_JoinState = EXEC_MJ_SKIPOUTER_ADVANCE;
                        break;
                    case MJEVAL_ENDOFJOIN:
                        /* No more outer tuples */
                        MJ_printf("ExecMergeJoin: end of outer subplan\n");
                        innerTupleSlot = node->mj_InnerTupleSlot;
                        if (doFillInner && !TupIsNull(innerTupleSlot))
                        {
                            /*
                             * Need to emit right-join tuples for remaining
                             * inner tuples.
                             */
                            node->mj_JoinState = EXEC_MJ_ENDOUTER;
                            break;
                        }
                        /* Otherwise we're done. */
                        return NULL;
                }
                break;
 
                /*
                 * EXEC_MJ_SKIPINNER_ADVANCE: advance over an inner tuple that
                 * is known not to join to any outer tuple.
                 *
                 * Before advancing, we check to see if we must emit an
                 * outer-join fill tuple for this inner tuple.
                 */
            case EXEC_MJ_SKIPINNER_ADVANCE:
                MJ_printf("ExecMergeJoin: EXEC_MJ_SKIPINNER_ADVANCE\n");
 
                if (doFillInner && !node->mj_MatchedInner)
                {
                    /*
                     * Generate a fake join tuple with nulls for the outer
                     * tuple, and return it if it passes the non-join quals.
                     */
                    TupleTableSlot *result;
 
                    node->mj_MatchedInner = true;   /* do it only once */
 
                    result = MJFillInner(node);
                    if (result)
                        return result;
                }
 
                /* Mark before advancing, if wanted */
                if (node->mj_ExtraMarks)
                    ExecMarkPos(innerPlan);
 
                /*
                 * now we get the next inner tuple, if any
                 */
                innerTupleSlot = ExecProcNode(innerPlan);
                node->mj_InnerTupleSlot = innerTupleSlot;
                MJ_DEBUG_PROC_NODE(innerTupleSlot);
                node->mj_MatchedInner = false;
 
                /* Compute join values and check for unmatchability */
                switch (MJEvalInnerValues(node, innerTupleSlot))
                {
                    case MJEVAL_MATCHABLE:
                        /* proceed to compare it to the current outer */
                        node->mj_JoinState = EXEC_MJ_SKIP_TEST;
                        break;
                    case MJEVAL_NONMATCHABLE:
 
                        /*
                         * current inner can't possibly match any outer;
                         * better to advance the inner scan than the outer.
                         */
                        node->mj_JoinState = EXEC_MJ_SKIPINNER_ADVANCE;
                        break;
                    case MJEVAL_ENDOFJOIN:
                        /* No more inner tuples */
                        MJ_printf("ExecMergeJoin: end of inner subplan\n");
                        outerTupleSlot = node->mj_OuterTupleSlot;
                        if (doFillOuter && !TupIsNull(outerTupleSlot))
                        {
                            /*
                             * Need to emit left-join tuples for remaining
                             * outer tuples.
                             */
                            node->mj_JoinState = EXEC_MJ_ENDINNER;
                            break;
                        }
                        /* Otherwise we're done. */
                        return NULL;
                }
                break;
 
                /*
                 * EXEC_MJ_ENDOUTER means we have run out of outer tuples, but
                 * are doing a right/right-anti/full join and therefore must
                 * null-fill any remaining unmatched inner tuples.
                 */
            case EXEC_MJ_ENDOUTER:
                MJ_printf("ExecMergeJoin: EXEC_MJ_ENDOUTER\n");
 
                Assert(doFillInner);
 
                if (!node->mj_MatchedInner)
                {
                    /*
                     * Generate a fake join tuple with nulls for the outer
                     * tuple, and return it if it passes the non-join quals.
                     */
                    TupleTableSlot *result;
 
                    node->mj_MatchedInner = true;   /* do it only once */
 
                    result = MJFillInner(node);
                    if (result)
                        return result;
                }
 
                /* Mark before advancing, if wanted */
                if (node->mj_ExtraMarks)
                    ExecMarkPos(innerPlan);
 
                /*
                 * now we get the next inner tuple, if any
                 */
                innerTupleSlot = ExecProcNode(innerPlan);
                node->mj_InnerTupleSlot = innerTupleSlot;
                MJ_DEBUG_PROC_NODE(innerTupleSlot);
                node->mj_MatchedInner = false;
 
                if (TupIsNull(innerTupleSlot))
                {
                    MJ_printf("ExecMergeJoin: end of inner subplan\n");
                    return NULL;
                }
 
                /* Else remain in ENDOUTER state and process next tuple. */
                break;
 
                /*
                 * EXEC_MJ_ENDINNER means we have run out of inner tuples, but
                 * are doing a left/full join and therefore must null- fill
                 * any remaining unmatched outer tuples.
                 */
            case EXEC_MJ_ENDINNER:
                MJ_printf("ExecMergeJoin: EXEC_MJ_ENDINNER\n");
 
                Assert(doFillOuter);
 
                if (!node->mj_MatchedOuter)
                {
                    /*
                     * Generate a fake join tuple with nulls for the inner
                     * tuple, and return it if it passes the non-join quals.
                     */
                    TupleTableSlot *result;
 
                    node->mj_MatchedOuter = true;   /* do it only once */
 
                    result = MJFillOuter(node);
                    if (result)
                        return result;
                }
 
                /*
                 * now we get the next outer tuple, if any
                 */
                outerTupleSlot = ExecProcNode(outerPlan);
                node->mj_OuterTupleSlot = outerTupleSlot;
                MJ_DEBUG_PROC_NODE(outerTupleSlot);
                node->mj_MatchedOuter = false;
 
                if (TupIsNull(outerTupleSlot))
                {
                    MJ_printf("ExecMergeJoin: end of outer subplan\n");
                    return NULL;
                }
 
                /* Else remain in ENDINNER state and process next tuple. */
                break;
 
                /*
                 * broken state value?
                 */
            default:
                elog(ERROR, "unrecognized mergejoin state: %d",
                     (int) node->mj_JoinState);
        }
    }
}
 
/* ----------------------------------------------------------------
 *      ExecInitMergeJoin
 * ----------------------------------------------------------------
 */
MergeJoinState *
ExecInitMergeJoin(MergeJoin *node, EState *estate, int eflags)
{
    MergeJoinState *mergestate;
    TupleDesc   outerDesc,
                innerDesc;
    const TupleTableSlotOps *innerOps;
 
    /* check for unsupported flags */
    Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
 
    MJ1_printf("ExecInitMergeJoin: %s\n",
               "initializing node");
 
    /*
     * create state structure
     */
    mergestate = makeNode(MergeJoinState);
    mergestate->js.ps.plan = (Plan *) node;
    mergestate->js.ps.state = estate;
    mergestate->js.ps.ExecProcNode = ExecMergeJoin;
    mergestate->js.jointype = node->join.jointype;
    mergestate->mj_ConstFalseJoin = false;
 
    /*
     * Miscellaneous initialization
     *
     * create expression context for node
     */
    ExecAssignExprContext(estate, &mergestate->js.ps);
 
    /*
     * we need two additional econtexts in which we can compute the join
     * expressions from the left and right input tuples.  The node's regular
     * econtext won't do because it gets reset too often.
     */
    mergestate->mj_OuterEContext = CreateExprContext(estate);
    mergestate->mj_InnerEContext = CreateExprContext(estate);
 
    /*
     * initialize child nodes
     *
     * inner child must support MARK/RESTORE, unless we have detected that we
     * don't need that.  Note that skip_mark_restore must never be set if
     * there are non-mergeclause joinquals, since the logic wouldn't work.
     */
    Assert(node->join.joinqual == NIL || !node->skip_mark_restore);
    mergestate->mj_SkipMarkRestore = node->skip_mark_restore;
 
    outerPlanState(mergestate) = ExecInitNode(outerPlan(node), estate, eflags);
    outerDesc = ExecGetResultType(outerPlanState(mergestate));
    innerPlanState(mergestate) = ExecInitNode(innerPlan(node), estate,
                                              mergestate->mj_SkipMarkRestore ?
                                              eflags :
                                              (eflags | EXEC_FLAG_MARK));
    innerDesc = ExecGetResultType(innerPlanState(mergestate));
 
    /*
     * For certain types of inner child nodes, it is advantageous to issue
     * MARK every time we advance past an inner tuple we will never return to.
     * For other types, MARK on a tuple we cannot return to is a waste of
     * cycles.  Detect which case applies and set mj_ExtraMarks if we want to
     * issue "unnecessary" MARK calls.
     *
     * Currently, only Material wants the extra MARKs, and it will be helpful
     * only if eflags doesn't specify REWIND.
     *
     * Note that for IndexScan and IndexOnlyScan, it is *necessary* that we
     * not set mj_ExtraMarks; otherwise we might attempt to set a mark before
     * the first inner tuple, which they do not support.
     */
    if (IsA(innerPlan(node), Material) &&
        (eflags & EXEC_FLAG_REWIND) == 0 &&
        !mergestate->mj_SkipMarkRestore)
        mergestate->mj_ExtraMarks = true;
    else
        mergestate->mj_ExtraMarks = false;
 
    /*
     * Initialize result slot, type and projection.
     */
    ExecInitResultTupleSlotTL(&mergestate->js.ps, &TTSOpsVirtual);
    ExecAssignProjectionInfo(&mergestate->js.ps, NULL);
 
    /*
     * tuple table initialization
     */
    innerOps = ExecGetResultSlotOps(innerPlanState(mergestate), NULL);
    mergestate->mj_MarkedTupleSlot = ExecInitExtraTupleSlot(estate, innerDesc,
                                                            innerOps);
 
    /*
     * initialize child expressions
     */
    mergestate->js.ps.qual =
        ExecInitQual(node->join.plan.qual, (PlanState *) mergestate);
    mergestate->js.joinqual =
        ExecInitQual(node->join.joinqual, (PlanState *) mergestate);
    /* mergeclauses are handled below */
 
    /*
     * detect whether we need only consider the first matching inner tuple
     */
    mergestate->js.single_match = (node->join.inner_unique ||
                                   node->join.jointype == JOIN_SEMI);
 
    /* set up null tuples for outer joins, if needed */
    switch (node->join.jointype)
    {
        case JOIN_INNER:
        case JOIN_SEMI:
            mergestate->mj_FillOuter = false;
            mergestate->mj_FillInner = false;
            break;
        case JOIN_LEFT:
        case JOIN_ANTI:
            mergestate->mj_FillOuter = true;
            mergestate->mj_FillInner = false;
            mergestate->mj_NullInnerTupleSlot =
                ExecInitNullTupleSlot(estate, innerDesc, &TTSOpsVirtual);
            break;
        case JOIN_RIGHT:
        case JOIN_RIGHT_ANTI:
            mergestate->mj_FillOuter = false;
            mergestate->mj_FillInner = true;
            mergestate->mj_NullOuterTupleSlot =
                ExecInitNullTupleSlot(estate, outerDesc, &TTSOpsVirtual);
 
            /*
             * Can't handle right, right-anti or full join with non-constant
             * extra joinclauses.  This should have been caught by planner.
             */
            if (!check_constant_qual(node->join.joinqual,
                                     &mergestate->mj_ConstFalseJoin))
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("RIGHT JOIN is only supported with merge-joinable join conditions")));
            break;
        case JOIN_FULL:
            mergestate->mj_FillOuter = true;
            mergestate->mj_FillInner = true;
            mergestate->mj_NullOuterTupleSlot =
                ExecInitNullTupleSlot(estate, outerDesc, &TTSOpsVirtual);
            mergestate->mj_NullInnerTupleSlot =
                ExecInitNullTupleSlot(estate, innerDesc, &TTSOpsVirtual);
 
            /*
             * Can't handle right, right-anti or full join with non-constant
             * extra joinclauses.  This should have been caught by planner.
             */
            if (!check_constant_qual(node->join.joinqual,
                                     &mergestate->mj_ConstFalseJoin))
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("FULL JOIN is only supported with merge-joinable join conditions")));
            break;
        default:
            elog(ERROR, "unrecognized join type: %d",
                 (int) node->join.jointype);
    }
 
    /*
     * preprocess the merge clauses
     */
    mergestate->mj_NumClauses = list_length(node->mergeclauses);
    mergestate->mj_Clauses = MJExamineQuals(node->mergeclauses,
                                            node->mergeFamilies,
                                            node->mergeCollations,
                                            node->mergeStrategies,
                                            node->mergeNullsFirst,
                                            (PlanState *) mergestate);
 
    /*
     * initialize join state
     */
    mergestate->mj_JoinState = EXEC_MJ_INITIALIZE_OUTER;
    mergestate->mj_MatchedOuter = false;
    mergestate->mj_MatchedInner = false;
    mergestate->mj_OuterTupleSlot = NULL;
    mergestate->mj_InnerTupleSlot = NULL;
 
    /*
     * initialization successful
     */
    MJ1_printf("ExecInitMergeJoin: %s\n",
               "node initialized");
 
    return mergestate;
}
 
/* ----------------------------------------------------------------
 *      ExecEndMergeJoin
 *
 * old comments
 *      frees storage allocated through C routines.
 * ----------------------------------------------------------------
 */
void
ExecEndMergeJoin(MergeJoinState *node)
{
    MJ1_printf("ExecEndMergeJoin: %s\n",
               "ending node processing");
 
    /*
     * shut down the subplans
     */
    ExecEndNode(innerPlanState(node));
    ExecEndNode(outerPlanState(node));
 
    MJ1_printf("ExecEndMergeJoin: %s\n",
               "node processing ended");
}
 
void
ExecReScanMergeJoin(MergeJoinState *node)
{
    PlanState  *outerPlan = outerPlanState(node);
    PlanState  *innerPlan = innerPlanState(node);
 
    ExecClearTuple(node->mj_MarkedTupleSlot);
 
    node->mj_JoinState = EXEC_MJ_INITIALIZE_OUTER;
    node->mj_MatchedOuter = false;
    node->mj_MatchedInner = false;
    node->mj_OuterTupleSlot = NULL;
    node->mj_InnerTupleSlot = NULL;
 
    /*
     * if chgParam of subnodes is not null then plans will be re-scanned by
     * first ExecProcNode.
     */
    if (outerPlan->chgParam == NULL)
        ExecReScan(outerPlan);
    if (innerPlan->chgParam == NULL)
        ExecReScan(innerPlan);
}