PostgreSQL在何处处理 sql查询之二十六

接前面，再次上溯一个层次，看代码(planmain.c :query_planner)：

void
query_planner(PlannerInfo *root, List *tlist,
              double tuple_fraction, double limit_tuples,
              Path **cheapest_path, Path **sorted_path,
              double *num_groups)
{
   ...

    /*
     * Make a flattened version of the rangetable for faster access (this is
     * OK because the rangetable won't change any more), and set up an empty
     * array for indexing base relations.
     */
    setup_simple_rel_arrays(root);

    /*
     * Construct RelOptInfo nodes for all base relations in query, and
     * indirectly for all appendrel member relations ("other rels").  This
     * will give us a RelOptInfo for every "simple" (non-join) rel involved in
     * the query.
     *
     * Note: the reason we find the rels by searching the jointree and
     * appendrel list, rather than just scanning the rangetable, is that the
     * rangetable may contain RTEs for rels not actively part of the query,
     * for example views.  We don't want to make RelOptInfos for them.
     */
    add_base_rels_to_query(root, (Node *) parse->jointree);
    /*
     * Examine the targetlist and join tree, adding entries to baserel
     * targetlists for all referenced Vars, and generating PlaceHolderInfo
     * entries for all referenced PlaceHolderVars.    Restrict and join clauses
     * are added to appropriate lists belonging to the mentioned relations. We
     * also build EquivalenceClasses for provably equivalent expressions. The
     * SpecialJoinInfo list is also built to hold information about join order
     * restrictions.  Finally, we form a target joinlist for make_one_rel() to
     * work from.
     */
    build_base_rel_tlists(root, tlist);

    find_placeholders_in_jointree(root);

    joinlist = deconstruct_jointree(root);

    /*
     * Reconsider any postponed outer-join quals now that we have built up
     * equivalence classes.  (This could result in further additions or
     * mergings of classes.)
     */
    reconsider_outer_join_clauses(root);

    /*
     * If we formed any equivalence classes, generate additional restriction
     * clauses as appropriate.    (Implied join clauses are formed on-the-fly
     * later.)
     */
    generate_base_implied_equalities(root);

    /*
     * We have completed merging equivalence sets, so it's now possible to
     * convert previously generated pathkeys (in particular, the requested
     * query_pathkeys) to canonical form.
     */
    canonicalize_all_pathkeys(root);

    /*
     * Examine any "placeholder" expressions generated during subquery pullup.
     * Make sure that the Vars they need are marked as needed at the relevant
     * join level.    This must be done before join removal because it might
     * cause Vars or placeholders to be needed above a join when they weren't
     * so marked before.
     */
    fix_placeholder_input_needed_levels(root);

    /*
     * Remove any useless outer joins.    Ideally this would be done during
     * jointree preprocessing, but the necessary information isn't available
     * until we've built baserel data structures and classified qual clauses.
     */
    joinlist = remove_useless_joins(root, joinlist);

    /*
     * Now distribute "placeholders" to base rels as needed.  This has to be
     * done after join removal because removal could change whether a
     * placeholder is evaluatable at a base rel.
     */
    add_placeholders_to_base_rels(root);
    ...
}

在此处，setup_simple_rel_arrays 构造了指向指针的数组（其实是指向指针数组的指针），挂在root下。 add_base_rels_to_query 要利用此数组。

看其中的代码(relnode.c)：

/*
 * setup_simple_rel_arrays
 *      Prepare the arrays we use for quickly accessing base relations.
 */
void
setup_simple_rel_arrays(PlannerInfo *root)
{
    Index        rti;
    ListCell   *lc;

    /* Arrays are accessed using RT indexes (1..N) */
    root->simple_rel_array_size = list_length(root->parse->rtable) + 1;

    /* simple_rel_array is initialized to all NULLs */
    root->simple_rel_array = (RelOptInfo **)
        palloc0(root->simple_rel_array_size * sizeof(RelOptInfo *));
    ...
    
}

add_base_rels_to_query ：(initsplan.c)

void
add_base_rels_to_query(PlannerInfo *root, Node *jtnode)
{
    if (jtnode == NULL)
        return;
    if (IsA(jtnode, RangeTblRef))
    {
        int    varno = ((RangeTblRef *) jtnode)->rtindex;
        (void) build_simple_rel(root, varno, RELOPT_BASEREL);
    }
    else if (IsA(jtnode, FromExpr))
    {
        FromExpr   *f = (FromExpr *) jtnode;
        ListCell   *l;

        foreach(l, f->fromlist)
            add_base_rels_to_query(root, lfirst(l));
    }
    else if (IsA(jtnode, JoinExpr))
    {
        JoinExpr   *j = (JoinExpr *) jtnode;

        add_base_rels_to_query(root, j->larg);
        add_base_rels_to_query(root, j->rarg);
    }
    else
        elog(ERROR, "unrecognized node type: %d",
             (int) nodeTag(jtnode));
}

build_simple_rel:

RelOptInfo *
build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
{
    RelOptInfo *rel;
    RangeTblEntry *rte;

    /* Rel should not exist already */
    Assert(relid > 0 && relid < root->simple_rel_array_size);
    if (root->simple_rel_array[relid] != NULL)
        elog(ERROR, "rel %d already exists", relid);
    ...

    /* Check type of rtable entry */
    switch (rte->rtekind)
    {
        case RTE_RELATION:
            /* Table --- retrieve statistics from the system catalogs */
            get_relation_info(root, rte->relid, rte->inh, rel);
            break;
        case RTE_SUBQUERY:
        case RTE_FUNCTION:
        case RTE_VALUES:
        case RTE_CTE:

            /*
             * Subquery, function, or values list --- set up attr range and
             * arrays
             *
             * Note: 0 is included in range to support whole-row Vars
             */
            rel->min_attr = 0;
            rel->max_attr = list_length(rte->eref->colnames);
            rel->attr_needed = (Relids *)
                palloc0((rel->max_attr - rel->min_attr + 1) * sizeof(Relids));
            rel->attr_widths = (int32 *)
                palloc0((rel->max_attr - rel->min_attr + 1) * sizeof(int32));
            break;
        default:
            elog(ERROR, "unrecognized RTE kind: %d",
                 (int) rte->rtekind);
            break;
    }

    /* Save the finished struct in the query's simple_rel_array */
    root->simple_rel_array[relid] = rel;

    ...

    return rel;
}