restrictinfo.c

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/*-------------------------------------------------------------------------
 *
 * restrictinfo.c
 *    RestrictInfo node manipulation routines.
 *
 * Portions Copyright (c) 1996-2017, 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/restrictinfo.h"
#include "optimizer/var.h"


static RestrictInfo *make_restrictinfo_internal(Expr *clause,
                           Expr *orclause,
                           bool is_pushed_down,
                           bool outerjoin_delayed,
                           bool pseudoconstant,
                           Index security_level,
                           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,
                       Index security_level,
                       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 security_level, 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,
                  Index security_level,
                  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,
                                                       security_level,
                                                       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,
                                      security_level,
                                      required_relids,
                                      outer_relids,
                                      nullable_relids);
}

/*
 * 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,
                           Index security_level,
                           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->security_level = security_level;
    restrictinfo->outer_relids = outer_relids;
    restrictinfo->nullable_relids = nullable_relids;

    /*
     * If it's potentially delayable by lower-level security quals, figure out
     * whether it's leakproof.  We can skip testing this for level-zero quals,
     * since they would never get delayed on security grounds anyway.
     */
    if (security_level > 0)
        restrictinfo->leakproof = !contain_leaked_vars((Node *) clause);
    else
        restrictinfo->leakproof = false;    /* really, "don't know" */

    /*
     * 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;
    restrictinfo->left_mcvfreq = -1;
    restrictinfo->right_mcvfreq = -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 security_level, 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,
                       Index security_level,
                       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,
                                                    security_level,
                                                    NULL,
                                                    outer_relids,
                                                    nullable_relids));
        return (Expr *) make_restrictinfo_internal(clause,
                                                   make_orclause(orlist),
                                                   is_pushed_down,
                                                   outerjoin_delayed,
                                                   pseudoconstant,
                                                   security_level,
                                                   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,
                                                     security_level,
                                                     required_relids,
                                                     outer_relids,
                                                     nullable_relids));
        return make_andclause(andlist);
    }
    else
        return (Expr *) make_restrictinfo_internal(clause,
                                                   NULL,
                                                   is_pushed_down,
                                                   outerjoin_delayed,
                                                   pseudoconstant,
                                                   security_level,
                                                   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;
}

/*
 * restriction_is_securely_promotable
 *
 * Returns true if it's okay to evaluate this clause "early", that is before
 * other restriction clauses attached to the specified relation.
 */
bool
restriction_is_securely_promotable(RestrictInfo *restrictinfo,
                                   RelOptInfo *rel)
{
    /*
     * It's okay if there are no baserestrictinfo clauses for the rel that
     * would need to go before this one, *or* if this one is leakproof.
     */
    if (restrictinfo->security_level <= rel->baserestrict_min_security ||
        restrictinfo->leakproof)
        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 = lfirst_node(RestrictInfo, l);

        Assert(!rinfo->pseudoconstant);

        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 = lfirst_node(RestrictInfo, l);

        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 = lfirst_node(RestrictInfo, l);

        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).
 *
 * Also 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.
 *
 * Also, the join clause must not use any relations that have LATERAL
 * references to the target relation, since we could not put such rels on
 * the outer side of a nestloop with the target relation.
 */
bool
join_clause_is_movable_to(RestrictInfo *rinfo, RelOptInfo *baserel)
{
    /* Clause must physically reference target rel */
    if (!bms_is_member(baserel->relid, rinfo->clause_relids))
        return false;

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

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

    /* Clause must not use any rels with LATERAL references to this rel */
    if (bms_overlap(baserel->lateral_referencers, rinfo->clause_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.
 *
 * The check about pushing a clause down into a lower outer join's inner side
 * is only approximate; it sometimes returns "false" when actually it would
 * be safe to use the clause here because we're still above the outer join
 * in question.  This is okay as long as the answers at different join levels
 * are consistent: it just means we might sometimes fail to push a clause as
 * far down as it could safely be pushed.  It's unclear whether it would be
 * worthwhile to do this more precisely.  (But if it's ever fixed to be
 * exactly accurate, there's an Assert in get_joinrel_parampathinfo() that
 * should be re-enabled.)
 *
 * There's no check here equivalent to join_clause_is_movable_to's test on
 * lateral_referencers.  We assume the caller wouldn't be inquiring unless
 * it'd verified that the proposed outer rels don't have lateral references
 * to the current rel(s).  (If we are considering join paths with the outer
 * rels on the outside and the current rels on the inside, then this should
 * have been checked at the outset of such consideration; see join_is_legal
 * and the path parameterization checks in joinpath.c.)  On the other hand,
 * in join_clause_is_movable_to we are asking whether the clause could be
 * moved for some valid set of outer rels, so we don't have the benefit of
 * relying on prior checks for lateral-reference validity.
 *
 * Note: if this returns true, it means that the clause could be moved to
 * this join relation, but that doesn't mean that this is the lowest join
 * it could be moved to.  Caller may need to make additional calls to verify
 * that this doesn't succeed on either of the inputs of a proposed join.
 *
 * 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 evaluable given available context */
    if (!bms_is_subset(rinfo->clause_relids, current_and_outer))
        return false;

    /* Clause must physically reference at least one target rel */
    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.  This is
     * approximate, in the safe direction, because the current join might be
     * above the join where the nulling would happen, in which case the clause
     * would work correctly here.  But we don't have enough info to be sure.
     */
    if (bms_overlap(currentrelids, rinfo->nullable_relids))
        return false;

    return true;
}