openGauss-server/src/gausskernel/optimizer/util/placeholder.cpp

/* -------------------------------------------------------------------------
 *
 * placeholder.cpp
 *	  PlaceHolderVar and PlaceHolderInfo manipulation routines
 *
 *
 * Portions Copyright (c) 2020 Huawei Technologies Co.,Ltd.
 * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/gausskernel/optimizer/util/placeholder.cpp
 *
 * -------------------------------------------------------------------------
 */
#include "postgres.h"
#include "knl/knl_variable.h"

#include "nodes/nodeFuncs.h"
#include "optimizer/cost.h"
#include "optimizer/pathnode.h"
#include "optimizer/placeholder.h"
#include "optimizer/planmain.h"
#include "optimizer/var.h"
#include "utils/lsyscache.h"

/* Local functions */
static void find_placeholders_recurse(PlannerInfo *root, Node *jtnode);
static void find_placeholders_in_expr(PlannerInfo *root, Node *expr);

/*
 * make_placeholder_expr
 *		Make a PlaceHolderVar for the given expression.
 *
 * phrels is the syntactic location (as a set of baserels) to attribute
 * to the expression.
 */
PlaceHolderVar* make_placeholder_expr(PlannerInfo* root, Expr* expr, Relids phrels)
{
    PlaceHolderVar* phv = makeNode(PlaceHolderVar);

    phv->phexpr = expr;
    phv->phrels = phrels;
    phv->phid = ++(root->glob->lastPHId);
    phv->phlevelsup = 0;

    return phv;
}

/*
 * find_placeholder_info
 *		Fetch the PlaceHolderInfo for the given PHV
 *
 * If the PlaceHolderInfo doesn't exist yet, create it if create_new_ph is
 * true, else throw an error.
 *
 * This is separate from make_placeholder_expr because subquery pullup has
 * to make PlaceHolderVars for expressions that might not be used at all in
 * the upper query, or might not remain after const-expression simplification.
 * We build PlaceHolderInfos only for PHVs that are still present in the
 * simplified query passed to query_planner().
 *
 * Note: this should only be called after query_planner() has started.	Also,
 * create_new_ph must not be TRUE after deconstruct_jointree begins, because
 * make_outerjoininfo assumes that we already know about all placeholders.
 */
PlaceHolderInfo* find_placeholder_info(PlannerInfo* root, PlaceHolderVar* phv, bool create_new_ph)
{
    PlaceHolderInfo* phinfo = NULL;
    ListCell* lc = NULL;

    /* if this ever isn't true, we'd need to be able to look in parent lists */
    AssertEreport(phv->phlevelsup == 0, MOD_OPT, "");

    foreach (lc, root->placeholder_list) {
        phinfo = (PlaceHolderInfo*)lfirst(lc);
        if (phinfo->phid == phv->phid)
            return phinfo;
    }

    /* Not found, so create it */
    if (!create_new_ph)
        ereport(ERROR,
            (errmodule(MOD_OPT),
                errcode(ERRCODE_OPTIMIZER_INCONSISTENT_STATE),
                errmsg("too late to create a new PlaceHolderInfo")));

    phinfo = makeNode(PlaceHolderInfo);

    phinfo->phid = phv->phid;
    phinfo->ph_var = (PlaceHolderVar*)copyObject(phv);
    phinfo->ph_eval_at = pull_varnos((Node*)phv);
    /* ph_eval_at may change later, see update_placeholder_eval_levels */
    phinfo->ph_needed = NULL; /* initially it's unused */
    /* for the moment, estimate width using just the datatype info */
    phinfo->ph_width = get_typavgwidth(exprType((Node*)phv->phexpr), exprTypmod((Node*)phv->phexpr));

    root->placeholder_list = lappend(root->placeholder_list, phinfo);

    /*
     * The PHV's contained expression may contain other, lower-level PHVs.  We
     * now know we need to get those into the PlaceHolderInfo list, too, so we
     * may as well do that immediately.
     */
    find_placeholders_in_expr(root, (Node *) phinfo->ph_var->phexpr);

    return phinfo;
}

/*
 * find_placeholders_in_jointree
 *		Search the jointree for PlaceHolderVars, and build PlaceHolderInfos
 *
 * We don't need to look at the targetlist because build_base_rel_tlists()
 * will already have made entries for any PHVs in the tlist.
 */
void find_placeholders_in_jointree(PlannerInfo* root)
{
    /* We need do nothing if the query contains no PlaceHolderVars */
    if (root->glob->lastPHId != 0) {
        /* Start recursion at top of jointree */
        AssertEreport(root->parse->jointree != NULL, MOD_OPT, "Join tree is null");
        AssertEreport(IsA(root->parse->jointree, FromExpr), MOD_OPT, "Join tree is not a FROM ... WHERE ... construct");
        (void)find_placeholders_recurse(root, (Node*)root->parse->jointree);
    }
}

/*
 * find_placeholders_recurse
 *	  One recursion level of find_placeholders_in_jointree.
 *
 * jtnode is the current jointree node to examine.
 *
 * The result is the set of base Relids contained in or below jtnode.
 * This is just an internal convenience, it's not used at the top level.
 */
static void find_placeholders_recurse(PlannerInfo* root, Node* jtnode)
{
    if (jtnode == NULL)
        return;
    if (IsA(jtnode, RangeTblRef)) {
        /* No quals to deal with here */
    } else if (IsA(jtnode, FromExpr)) {
        FromExpr* f = (FromExpr*)jtnode;
        ListCell* l = NULL;

        /*
         * First, recurse to handle child joins.
         */
        foreach (l, f->fromlist) {
            find_placeholders_recurse(root, (Node *)lfirst(l));
        }

        /*
         * Now process the top-level quals.
         */
        find_placeholders_in_expr(root, f->quals);
    } else if (IsA(jtnode, JoinExpr)) {
        JoinExpr* j = (JoinExpr*)jtnode;

        /*
         * First, recurse to handle child joins.
         */
        find_placeholders_recurse(root, j->larg);
        find_placeholders_recurse(root, j->rarg);

        /* Process the qual clauses */
        find_placeholders_in_expr(root, j->quals);
    } else {
        ereport(ERROR,
            (errmodule(MOD_OPT),
                errcode(ERRCODE_UNRECOGNIZED_NODE_TYPE),
                errmsg("unrecognized node type: %d", (int)nodeTag(jtnode))));
    }
}

/*
 * find_placeholders_in_expr
 *      Find all PlaceHolderVars in the given expression, and create
 *      PlaceHolderInfo entries for them.
 */
static void find_placeholders_in_expr(PlannerInfo *root, Node *expr)
{
    List* vars = NIL;
    ListCell* vl = NULL;

    /*
     * pull_var_clause does more than we need here, but it'll do and it's
     * convenient to use.
     */
    vars = pull_var_clause(expr, PVC_RECURSE_AGGREGATES, PVC_INCLUDE_PLACEHOLDERS);
    foreach (vl, vars) {
        PlaceHolderVar* phv = (PlaceHolderVar*)lfirst(vl);

        /* Ignore any plain Vars */
        if (!IsA(phv, PlaceHolderVar))
            continue;

        /* Create a PlaceHolderInfo entry if there's not one already */
        (void) find_placeholder_info(root, phv, true);
    }
    list_free_ext(vars);
}

/*
 * update_placeholder_eval_levels
 *		Adjust the target evaluation levels for placeholders
 *
 * The initial eval_at level set by find_placeholder_info was the set of
 * rels used in the placeholder's expression (or the whole subselect below
 * the placeholder's syntactic location, if the expr is variable-free).
 * If the subselect contains any outer joins that can null any of those rels,
 * we must delay evaluation to above those joins.
 *
 * We repeat this operation each time we add another outer join to
 * root->join_info_list.  It's somewhat annoying to have to do that, but
 * since we don't have very much information on the placeholders' locations,
 * it's hard to avoid.  Each placeholder's eval_at level must be correct
 * by the time it starts to figure in outer-join delay decisions for higher
 * outer joins.
 *
 * In future we might want to put additional policy/heuristics here to
 * try to determine an optimal evaluation level.  The current rules will
 * result in evaluation at the lowest possible level.  However, pushing a
 * placeholder eval up the tree is likely to further constrain evaluation
 * order for outer joins, so it could easily be counterproductive; and we
 * don't have enough information at this point to make an intelligent choice.
 */
void update_placeholder_eval_levels(PlannerInfo* root, SpecialJoinInfo* new_sjinfo)
{
    ListCell* lc1 = NULL;

    foreach (lc1, root->placeholder_list) {
        PlaceHolderInfo* phinfo = (PlaceHolderInfo*)lfirst(lc1);
        Relids syn_level = phinfo->ph_var->phrels;
        Relids eval_at;
        bool found_some = false;
        ListCell* lc2 = NULL;

        /*
         * We don't need to do any work on this placeholder unless the
         * newly-added outer join is syntactically beneath its location.
         */
        if (!bms_is_subset(new_sjinfo->syn_lefthand, syn_level) || !bms_is_subset(new_sjinfo->syn_righthand, syn_level))
            continue;

        /*
         * Check for delays due to lower outer joins.  This is the same logic
         * as in check_outerjoin_delay in initsplan.c, except that we don't
         * have anything to do with the delay_upper_joins flags; delay of
         * upper outer joins will be handled later, based on the eval_at
         * values we compute now.
         */
        eval_at = phinfo->ph_eval_at;

        do {
            found_some = false;
            foreach (lc2, root->join_info_list) {
                SpecialJoinInfo* sjinfo = (SpecialJoinInfo*)lfirst(lc2);

                /* disregard joins not within the PHV's sub-select */
                if (!bms_is_subset(sjinfo->syn_lefthand, syn_level) || !bms_is_subset(sjinfo->syn_righthand, syn_level))
                    continue;

                /* do we reference any nullable rels of this OJ? */
                if (bms_overlap(eval_at, sjinfo->min_righthand) ||
                    (sjinfo->jointype == JOIN_FULL && bms_overlap(eval_at, sjinfo->min_lefthand))) {
                    /* yes; have we included all its rels in eval_at? */
                    if (!bms_is_subset(sjinfo->min_lefthand, eval_at) ||
                        !bms_is_subset(sjinfo->min_righthand, eval_at)) {
                        /* no, so add them in */
                        eval_at = bms_add_members(eval_at, sjinfo->min_lefthand);
                        eval_at = bms_add_members(eval_at, sjinfo->min_righthand);
                        /* we'll need another iteration */
                        found_some = true;
                    }
                }
            }
        } while (found_some);

        phinfo->ph_eval_at = eval_at;
    }
}

/*
 * fix_placeholder_input_needed_levels
 *		Adjust the "needed at" levels for placeholder inputs
 *
 * This is called after we've finished determining the eval_at levels for
 * all placeholders.  We need to make sure that all vars and placeholders
 * needed to evaluate each placeholder will be available at the join level
 * where the evaluation will be done.  Note that this loop can have
 * side-effects on the ph_needed sets of other PlaceHolderInfos; that's okay
 * because we don't examine ph_needed here, so there are no ordering issues
 * to worry about.
 */
void fix_placeholder_input_needed_levels(PlannerInfo* root)
{
    ListCell* lc = NULL;

    foreach (lc, root->placeholder_list) {
        PlaceHolderInfo* phinfo = (PlaceHolderInfo*)lfirst(lc);
        Relids eval_at = phinfo->ph_eval_at;

        /* No work unless it'll be evaluated above baserel level */
        if (bms_membership(eval_at) == BMS_MULTIPLE) {
            List* vars =
                pull_var_clause((Node*)phinfo->ph_var->phexpr, PVC_RECURSE_AGGREGATES, PVC_INCLUDE_PLACEHOLDERS);

            add_vars_to_targetlist(root, vars, eval_at, false);
            list_free_ext(vars);
        }
    }
}

/*
 * add_placeholders_to_base_rels
 *		Add any required PlaceHolderVars to base rels' targetlists.
 *
 * If any placeholder can be computed at a base rel and is needed above it,
 * add it to that rel's targetlist.  This might look like it could be merged
 * with fix_placeholder_input_needed_levels, but it must be separate because
 * join removal happens in between, and can change the ph_eval_at sets.  There
 * is essentially the same logic in add_placeholders_to_joinrel, but we can't
 * do that part until joinrels are formed.
 */
void add_placeholders_to_base_rels(PlannerInfo* root)
{
    ListCell* lc = NULL;

    foreach (lc, root->placeholder_list) {
        PlaceHolderInfo* phinfo = (PlaceHolderInfo*)lfirst(lc);
        Relids eval_at = phinfo->ph_eval_at;

        if (bms_membership(eval_at) == BMS_SINGLETON &&
            bms_nonempty_difference(phinfo->ph_needed, eval_at)) {
            int varno = bms_singleton_member(eval_at);
            RelOptInfo* rel = find_base_rel(root, varno);

            rel->reltargetlist = lappend(rel->reltargetlist, copyObject(phinfo->ph_var));
        }
    }
}

/*
 * add_placeholders_to_joinrel
 *		Add any required PlaceHolderVars to a join rel's targetlist.
 *
 * A join rel should emit a PlaceHolderVar if (a) the PHV is needed above
 * this join level and (b) the PHV can be computed at or below this level.
 * At this time we do not need to distinguish whether the PHV will be
 * computed here or copied up from below.
 */
void add_placeholders_to_joinrel(PlannerInfo* root, RelOptInfo* joinrel)
{
    Relids relids = joinrel->relids;
    ListCell* lc = NULL;

    foreach (lc, root->placeholder_list) {
        PlaceHolderInfo* phinfo = (PlaceHolderInfo*)lfirst(lc);

        /* Is it still needed above this joinrel? */
        if (bms_nonempty_difference(phinfo->ph_needed, relids)) {
            /* Is it computable here? */
            if (bms_is_subset(phinfo->ph_eval_at, relids)) {
                /* Yup, add it to the output */
                joinrel->reltargetlist = lappend(joinrel->reltargetlist, phinfo->ph_var);
                joinrel->width += phinfo->ph_width;
                if (root->glob->vectorized) {
                    joinrel->encodedwidth += columnar_get_col_width(exprType((Node*)phinfo->ph_var), phinfo->ph_width);
                    joinrel->encodednum++;
                }
            }
        }
    }
}