restrictinfo.c

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/*-------------------------------------------------------------------------
 *
 * restrictinfo.c
 *    RestrictInfo node manipulation routines.
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/optimizer/util/restrictinfo.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "optimizer/clauses.h"
#include "optimizer/predtest.h"
#include "optimizer/restrictinfo.h"
#include "optimizer/var.h"


static RestrictInfo *make_restrictinfo_internal(Expr *clause,
                           Expr *orclause,
                           bool is_pushed_down,
                           bool outerjoin_delayed,
                           bool pseudoconstant,
                           Relids required_relids,
                           Relids outer_relids,
                           Relids nullable_relids);
static Expr *make_sub_restrictinfos(Expr *clause,
                       bool is_pushed_down,
                       bool outerjoin_delayed,
                       bool pseudoconstant,
                       Relids required_relids,
                       Relids outer_relids,
                       Relids nullable_relids);


/*
 * make_restrictinfo
 *
 * Build a RestrictInfo node containing the given subexpression.
 *
 * The is_pushed_down, outerjoin_delayed, and pseudoconstant flags for the
 * RestrictInfo must be supplied by the caller, as well as the correct values
 * for outer_relids and nullable_relids.
 * required_relids can be NULL, in which case it defaults to the actual clause
 * contents (i.e., clause_relids).
 *
 * We initialize fields that depend only on the given subexpression, leaving
 * others that depend on context (or may never be needed at all) to be filled
 * later.
 */
RestrictInfo *
make_restrictinfo(Expr *clause,
                  bool is_pushed_down,
                  bool outerjoin_delayed,
                  bool pseudoconstant,
                  Relids required_relids,
                  Relids outer_relids,
                  Relids nullable_relids)
{
    /*
     * If it's an OR clause, build a modified copy with RestrictInfos inserted
     * above each subclause of the top-level AND/OR structure.
     */
    if (or_clause((Node *) clause))
        return (RestrictInfo *) make_sub_restrictinfos(clause,
                                                       is_pushed_down,
                                                       outerjoin_delayed,
                                                       pseudoconstant,
                                                       required_relids,
                                                       outer_relids,
                                                       nullable_relids);

    /* Shouldn't be an AND clause, else AND/OR flattening messed up */
    Assert(!and_clause((Node *) clause));

    return make_restrictinfo_internal(clause,
                                      NULL,
                                      is_pushed_down,
                                      outerjoin_delayed,
                                      pseudoconstant,
                                      required_relids,
                                      outer_relids,
                                      nullable_relids);
}

/*
 * make_restrictinfo_from_bitmapqual
 *
 * Given the bitmapqual Path structure for a bitmap indexscan, generate
 * RestrictInfo node(s) equivalent to the condition represented by the
 * indexclauses of the Path structure.
 *
 * The result is a List (effectively, implicit-AND representation) of
 * RestrictInfos.
 *
 * The caller must pass is_pushed_down, but we assume outerjoin_delayed
 * and pseudoconstant are false while outer_relids and nullable_relids
 * are NULL (no other kind of qual should ever get into a bitmapqual).
 *
 * If include_predicates is true, we add any partial index predicates to
 * the explicit index quals.  When this is not true, we return a condition
 * that might be weaker than the actual scan represents.
 *
 * To do this through the normal make_restrictinfo() API, callers would have
 * to strip off the RestrictInfo nodes present in the indexclauses lists, and
 * then make_restrictinfo() would have to build new ones.  It's better to have
 * a specialized routine to allow sharing of RestrictInfos.
 *
 * The qual manipulations here are much the same as in create_bitmap_subplan;
 * keep the two routines in sync!
 */
List *
make_restrictinfo_from_bitmapqual(Path *bitmapqual,
                                  bool is_pushed_down,
                                  bool include_predicates)
{
    List       *result;
    ListCell   *l;

    if (IsA(bitmapqual, BitmapAndPath))
    {
        BitmapAndPath *apath = (BitmapAndPath *) bitmapqual;

        /*
         * There may well be redundant quals among the subplans, since a
         * top-level WHERE qual might have gotten used to form several
         * different index quals.  We don't try exceedingly hard to eliminate
         * redundancies, but we do eliminate obvious duplicates by using
         * list_concat_unique.
         */
        result = NIL;
        foreach(l, apath->bitmapquals)
        {
            List       *sublist;

            sublist = make_restrictinfo_from_bitmapqual((Path *) lfirst(l),
                                                        is_pushed_down,
                                                        include_predicates);
            result = list_concat_unique(result, sublist);
        }
    }
    else if (IsA(bitmapqual, BitmapOrPath))
    {
        BitmapOrPath *opath = (BitmapOrPath *) bitmapqual;
        List       *withris = NIL;
        List       *withoutris = NIL;

        /*
         * Here, we only detect qual-free subplans.  A qual-free subplan would
         * cause us to generate "... OR true ..."  which we may as well reduce
         * to just "true".  We do not try to eliminate redundant subclauses
         * because (a) it's not as likely as in the AND case, and (b) we might
         * well be working with hundreds or even thousands of OR conditions,
         * perhaps from a long IN list.  The performance of list_append_unique
         * would be unacceptable.
         */
        foreach(l, opath->bitmapquals)
        {
            List       *sublist;

            sublist = make_restrictinfo_from_bitmapqual((Path *) lfirst(l),
                                                        is_pushed_down,
                                                        include_predicates);
            if (sublist == NIL)
            {
                /*
                 * If we find a qual-less subscan, it represents a constant
                 * TRUE, and hence the OR result is also constant TRUE, so we
                 * can stop here.
                 */
                return NIL;
            }

            /*
             * If the sublist contains multiple RestrictInfos, we create an
             * AND subclause.  If there's just one, we have to check if it's
             * an OR clause, and if so flatten it to preserve AND/OR flatness
             * of our output.
             *
             * We construct lists with and without sub-RestrictInfos, so as
             * not to have to regenerate duplicate RestrictInfos below.
             */
            if (list_length(sublist) > 1)
            {
                withris = lappend(withris, make_andclause(sublist));
                sublist = get_actual_clauses(sublist);
                withoutris = lappend(withoutris, make_andclause(sublist));
            }
            else
            {
                RestrictInfo *subri = (RestrictInfo *) linitial(sublist);

                Assert(IsA(subri, RestrictInfo));
                if (restriction_is_or_clause(subri))
                {
                    BoolExpr   *subor = (BoolExpr *) subri->orclause;

                    Assert(or_clause((Node *) subor));
                    withris = list_concat(withris,
                                          list_copy(subor->args));
                    subor = (BoolExpr *) subri->clause;
                    Assert(or_clause((Node *) subor));
                    withoutris = list_concat(withoutris,
                                             list_copy(subor->args));
                }
                else
                {
                    withris = lappend(withris, subri);
                    withoutris = lappend(withoutris, subri->clause);
                }
            }
        }

        /*
         * Avoid generating one-element ORs, which could happen due to
         * redundancy elimination or ScalarArrayOpExpr quals.
         */
        if (list_length(withris) <= 1)
            result = withris;
        else
        {
            /* Here's the magic part not available to outside callers */
            result =
                list_make1(make_restrictinfo_internal(make_orclause(withoutris),
                                                      make_orclause(withris),
                                                      is_pushed_down,
                                                      false,
                                                      false,
                                                      NULL,
                                                      NULL,
                                                      NULL));
        }
    }
    else if (IsA(bitmapqual, IndexPath))
    {
        IndexPath  *ipath = (IndexPath *) bitmapqual;

        result = list_copy(ipath->indexclauses);
        if (include_predicates && ipath->indexinfo->indpred != NIL)
        {
            foreach(l, ipath->indexinfo->indpred)
            {
                Expr       *pred = (Expr *) lfirst(l);

                /*
                 * We know that the index predicate must have been implied by
                 * the query condition as a whole, but it may or may not be
                 * implied by the conditions that got pushed into the
                 * bitmapqual.  Avoid generating redundant conditions.
                 */
                if (!predicate_implied_by(list_make1(pred), result))
                    result = lappend(result,
                                     make_restrictinfo(pred,
                                                       is_pushed_down,
                                                       false,
                                                       false,
                                                       NULL,
                                                       NULL,
                                                       NULL));
            }
        }
    }
    else
    {
        elog(ERROR, "unrecognized node type: %d", nodeTag(bitmapqual));
        result = NIL;           /* keep compiler quiet */
    }

    return result;
}

/*
 * make_restrictinfos_from_actual_clauses
 *
 * Given a list of implicitly-ANDed restriction clauses, produce a list
 * of RestrictInfo nodes.  This is used to reconstitute the RestrictInfo
 * representation after doing transformations of a list of clauses.
 *
 * We assume that the clauses are relation-level restrictions and therefore
 * we don't have to worry about is_pushed_down, outerjoin_delayed,
 * outer_relids, and nullable_relids (these can be assumed true, false,
 * NULL, and NULL, respectively).
 * We do take care to recognize pseudoconstant clauses properly.
 */
List *
make_restrictinfos_from_actual_clauses(PlannerInfo *root,
                                       List *clause_list)
{
    List       *result = NIL;
    ListCell   *l;

    foreach(l, clause_list)
    {
        Expr       *clause = (Expr *) lfirst(l);
        bool        pseudoconstant;
        RestrictInfo *rinfo;

        /*
         * It's pseudoconstant if it contains no Vars and no volatile
         * functions.  We probably can't see any sublinks here, so
         * contain_var_clause() would likely be enough, but for safety use
         * contain_vars_of_level() instead.
         */
        pseudoconstant =
            !contain_vars_of_level((Node *) clause, 0) &&
            !contain_volatile_functions((Node *) clause);
        if (pseudoconstant)
        {
            /* tell createplan.c to check for gating quals */
            root->hasPseudoConstantQuals = true;
        }

        rinfo = make_restrictinfo(clause,
                                  true,
                                  false,
                                  pseudoconstant,
                                  NULL,
                                  NULL,
                                  NULL);
        result = lappend(result, rinfo);
    }
    return result;
}

/*
 * make_restrictinfo_internal
 *
 * Common code for the main entry points and the recursive cases.
 */
static RestrictInfo *
make_restrictinfo_internal(Expr *clause,
                           Expr *orclause,
                           bool is_pushed_down,
                           bool outerjoin_delayed,
                           bool pseudoconstant,
                           Relids required_relids,
                           Relids outer_relids,
                           Relids nullable_relids)
{
    RestrictInfo *restrictinfo = makeNode(RestrictInfo);

    restrictinfo->clause = clause;
    restrictinfo->orclause = orclause;
    restrictinfo->is_pushed_down = is_pushed_down;
    restrictinfo->outerjoin_delayed = outerjoin_delayed;
    restrictinfo->pseudoconstant = pseudoconstant;
    restrictinfo->can_join = false;     /* may get set below */
    restrictinfo->outer_relids = outer_relids;
    restrictinfo->nullable_relids = nullable_relids;

    /*
     * If it's a binary opclause, set up left/right relids info. In any case
     * set up the total clause relids info.
     */
    if (is_opclause(clause) && list_length(((OpExpr *) clause)->args) == 2)
    {
        restrictinfo->left_relids = pull_varnos(get_leftop(clause));
        restrictinfo->right_relids = pull_varnos(get_rightop(clause));

        restrictinfo->clause_relids = bms_union(restrictinfo->left_relids,
                                                restrictinfo->right_relids);

        /*
         * Does it look like a normal join clause, i.e., a binary operator
         * relating expressions that come from distinct relations? If so we
         * might be able to use it in a join algorithm.  Note that this is a
         * purely syntactic test that is made regardless of context.
         */
        if (!bms_is_empty(restrictinfo->left_relids) &&
            !bms_is_empty(restrictinfo->right_relids) &&
            !bms_overlap(restrictinfo->left_relids,
                         restrictinfo->right_relids))
        {
            restrictinfo->can_join = true;
            /* pseudoconstant should certainly not be true */
            Assert(!restrictinfo->pseudoconstant);
        }
    }
    else
    {
        /* Not a binary opclause, so mark left/right relid sets as empty */
        restrictinfo->left_relids = NULL;
        restrictinfo->right_relids = NULL;
        /* and get the total relid set the hard way */
        restrictinfo->clause_relids = pull_varnos((Node *) clause);
    }

    /* required_relids defaults to clause_relids */
    if (required_relids != NULL)
        restrictinfo->required_relids = required_relids;
    else
        restrictinfo->required_relids = restrictinfo->clause_relids;

    /*
     * Fill in all the cacheable fields with "not yet set" markers. None of
     * these will be computed until/unless needed.  Note in particular that we
     * don't mark a binary opclause as mergejoinable or hashjoinable here;
     * that happens only if it appears in the right context (top level of a
     * joinclause list).
     */
    restrictinfo->parent_ec = NULL;

    restrictinfo->eval_cost.startup = -1;
    restrictinfo->norm_selec = -1;
    restrictinfo->outer_selec = -1;

    restrictinfo->mergeopfamilies = NIL;

    restrictinfo->left_ec = NULL;
    restrictinfo->right_ec = NULL;
    restrictinfo->left_em = NULL;
    restrictinfo->right_em = NULL;
    restrictinfo->scansel_cache = NIL;

    restrictinfo->outer_is_left = false;

    restrictinfo->hashjoinoperator = InvalidOid;

    restrictinfo->left_bucketsize = -1;
    restrictinfo->right_bucketsize = -1;

    return restrictinfo;
}

/*
 * Recursively insert sub-RestrictInfo nodes into a boolean expression.
 *
 * We put RestrictInfos above simple (non-AND/OR) clauses and above
 * sub-OR clauses, but not above sub-AND clauses, because there's no need.
 * This may seem odd but it is closely related to the fact that we use
 * implicit-AND lists at top level of RestrictInfo lists.  Only ORs and
 * simple clauses are valid RestrictInfos.
 *
 * The same is_pushed_down, outerjoin_delayed, and pseudoconstant flag
 * values can be applied to all RestrictInfo nodes in the result.  Likewise
 * for outer_relids and nullable_relids.
 *
 * The given required_relids are attached to our top-level output,
 * but any OR-clause constituents are allowed to default to just the
 * contained rels.
 */
static Expr *
make_sub_restrictinfos(Expr *clause,
                       bool is_pushed_down,
                       bool outerjoin_delayed,
                       bool pseudoconstant,
                       Relids required_relids,
                       Relids outer_relids,
                       Relids nullable_relids)
{
    if (or_clause((Node *) clause))
    {
        List       *orlist = NIL;
        ListCell   *temp;

        foreach(temp, ((BoolExpr *) clause)->args)
            orlist = lappend(orlist,
                             make_sub_restrictinfos(lfirst(temp),
                                                    is_pushed_down,
                                                    outerjoin_delayed,
                                                    pseudoconstant,
                                                    NULL,
                                                    outer_relids,
                                                    nullable_relids));
        return (Expr *) make_restrictinfo_internal(clause,
                                                   make_orclause(orlist),
                                                   is_pushed_down,
                                                   outerjoin_delayed,
                                                   pseudoconstant,
                                                   required_relids,
                                                   outer_relids,
                                                   nullable_relids);
    }
    else if (and_clause((Node *) clause))
    {
        List       *andlist = NIL;
        ListCell   *temp;

        foreach(temp, ((BoolExpr *) clause)->args)
            andlist = lappend(andlist,
                              make_sub_restrictinfos(lfirst(temp),
                                                     is_pushed_down,
                                                     outerjoin_delayed,
                                                     pseudoconstant,
                                                     required_relids,
                                                     outer_relids,
                                                     nullable_relids));
        return make_andclause(andlist);
    }
    else
        return (Expr *) make_restrictinfo_internal(clause,
                                                   NULL,
                                                   is_pushed_down,
                                                   outerjoin_delayed,
                                                   pseudoconstant,
                                                   required_relids,
                                                   outer_relids,
                                                   nullable_relids);
}

/*
 * restriction_is_or_clause
 *
 * Returns t iff the restrictinfo node contains an 'or' clause.
 */
bool
restriction_is_or_clause(RestrictInfo *restrictinfo)
{
    if (restrictinfo->orclause != NULL)
        return true;
    else
        return false;
}

/*
 * get_actual_clauses
 *
 * Returns a list containing the bare clauses from 'restrictinfo_list'.
 *
 * This is only to be used in cases where none of the RestrictInfos can
 * be pseudoconstant clauses (for instance, it's OK on indexqual lists).
 */
List *
get_actual_clauses(List *restrictinfo_list)
{
    List       *result = NIL;
    ListCell   *l;

    foreach(l, restrictinfo_list)
    {
        RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);

        Assert(IsA(rinfo, RestrictInfo));

        Assert(!rinfo->pseudoconstant);

        result = lappend(result, rinfo->clause);
    }
    return result;
}

/*
 * get_all_actual_clauses
 *
 * Returns a list containing the bare clauses from 'restrictinfo_list'.
 *
 * This loses the distinction between regular and pseudoconstant clauses,
 * so be careful what you use it for.
 */
List *
get_all_actual_clauses(List *restrictinfo_list)
{
    List       *result = NIL;
    ListCell   *l;

    foreach(l, restrictinfo_list)
    {
        RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);

        Assert(IsA(rinfo, RestrictInfo));

        result = lappend(result, rinfo->clause);
    }
    return result;
}

/*
 * extract_actual_clauses
 *
 * Extract bare clauses from 'restrictinfo_list', returning either the
 * regular ones or the pseudoconstant ones per 'pseudoconstant'.
 */
List *
extract_actual_clauses(List *restrictinfo_list,
                       bool pseudoconstant)
{
    List       *result = NIL;
    ListCell   *l;

    foreach(l, restrictinfo_list)
    {
        RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);

        Assert(IsA(rinfo, RestrictInfo));

        if (rinfo->pseudoconstant == pseudoconstant)
            result = lappend(result, rinfo->clause);
    }
    return result;
}

/*
 * extract_actual_join_clauses
 *
 * Extract bare clauses from 'restrictinfo_list', separating those that
 * syntactically match the join level from those that were pushed down.
 * Pseudoconstant clauses are excluded from the results.
 *
 * This is only used at outer joins, since for plain joins we don't care
 * about pushed-down-ness.
 */
void
extract_actual_join_clauses(List *restrictinfo_list,
                            List **joinquals,
                            List **otherquals)
{
    ListCell   *l;

    *joinquals = NIL;
    *otherquals = NIL;

    foreach(l, restrictinfo_list)
    {
        RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);

        Assert(IsA(rinfo, RestrictInfo));

        if (rinfo->is_pushed_down)
        {
            if (!rinfo->pseudoconstant)
                *otherquals = lappend(*otherquals, rinfo->clause);
        }
        else
        {
            /* joinquals shouldn't have been marked pseudoconstant */
            Assert(!rinfo->pseudoconstant);
            *joinquals = lappend(*joinquals, rinfo->clause);
        }
    }
}


/*
 * join_clause_is_movable_to
 *      Test whether a join clause is a safe candidate for parameterization
 *      of a scan on the specified base relation.
 *
 * A movable join clause is one that can safely be evaluated at a rel below
 * its normal semantic level (ie, its required_relids), if the values of
 * variables that it would need from other rels are provided.
 *
 * We insist that the clause actually reference the target relation; this
 * prevents undesirable movement of degenerate join clauses, and ensures
 * that there is a unique place that a clause can be moved down to.
 *
 * We cannot move an outer-join clause into the non-nullable side of its
 * outer join, as that would change the results (rows would be suppressed
 * rather than being null-extended).
 *
 * And the target relation must not be in the clause's nullable_relids, i.e.,
 * there must not be an outer join below the clause that would null the Vars
 * coming from the target relation.  Otherwise the clause might give results
 * different from what it would give at its normal semantic level.
 */
bool
join_clause_is_movable_to(RestrictInfo *rinfo, Index baserelid)
{
    /* Clause must physically reference target rel */
    if (!bms_is_member(baserelid, rinfo->clause_relids))
        return false;

    /* Cannot move an outer-join clause into the join's outer side */
    if (bms_is_member(baserelid, rinfo->outer_relids))
        return false;

    /* Target rel must not be nullable below the clause */
    if (bms_is_member(baserelid, rinfo->nullable_relids))
        return false;

    return true;
}

/*
 * join_clause_is_movable_into
 *      Test whether a join clause is movable and can be evaluated within
 *      the current join context.
 *
 * currentrelids: the relids of the proposed evaluation location
 * current_and_outer: the union of currentrelids and the required_outer
 *      relids (parameterization's outer relations)
 *
 * The API would be a bit clearer if we passed the current relids and the
 * outer relids separately and did bms_union internally; but since most
 * callers need to apply this function to multiple clauses, we make the
 * caller perform the union.
 *
 * Obviously, the clause must only refer to Vars available from the current
 * relation plus the outer rels.  We also check that it does reference at
 * least one current Var, ensuring that the clause will be pushed down to
 * a unique place in a parameterized join tree.  And we check that we're
 * not pushing the clause into its outer-join outer side, nor down into
 * a lower outer join's inner side.
 *
 * Note: get_joinrel_parampathinfo depends on the fact that if
 * current_and_outer is NULL, this function will always return false
 * (since one or the other of the first two tests must fail).
 */
bool
join_clause_is_movable_into(RestrictInfo *rinfo,
                            Relids currentrelids,
                            Relids current_and_outer)
{
    /* Clause must be evaluatable given available context */
    if (!bms_is_subset(rinfo->clause_relids, current_and_outer))
        return false;

    /* Clause must physically reference target rel(s) */
    if (!bms_overlap(currentrelids, rinfo->clause_relids))
        return false;

    /* Cannot move an outer-join clause into the join's outer side */
    if (bms_overlap(currentrelids, rinfo->outer_relids))
        return false;

    /* Target rel(s) must not be nullable below the clause */
    if (bms_overlap(currentrelids, rinfo->nullable_relids))
        return false;

    return true;
}