LCOV - code coverage report
Current view: top level - src/backend/optimizer/plan - planmain.c (source / functions) Hit Total Coverage
Test: PostgreSQL 13devel Lines: 54 55 98.2 %
Date: 2019-11-22 06:06:53 Functions: 1 1 100.0 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * planmain.c
       4             :  *    Routines to plan a single query
       5             :  *
       6             :  * What's in a name, anyway?  The top-level entry point of the planner/
       7             :  * optimizer is over in planner.c, not here as you might think from the
       8             :  * file name.  But this is the main code for planning a basic join operation,
       9             :  * shorn of features like subselects, inheritance, aggregates, grouping,
      10             :  * and so on.  (Those are the things planner.c deals with.)
      11             :  *
      12             :  * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
      13             :  * Portions Copyright (c) 1994, Regents of the University of California
      14             :  *
      15             :  *
      16             :  * IDENTIFICATION
      17             :  *    src/backend/optimizer/plan/planmain.c
      18             :  *
      19             :  *-------------------------------------------------------------------------
      20             :  */
      21             : #include "postgres.h"
      22             : 
      23             : #include "optimizer/appendinfo.h"
      24             : #include "optimizer/clauses.h"
      25             : #include "optimizer/inherit.h"
      26             : #include "optimizer/optimizer.h"
      27             : #include "optimizer/orclauses.h"
      28             : #include "optimizer/pathnode.h"
      29             : #include "optimizer/paths.h"
      30             : #include "optimizer/placeholder.h"
      31             : #include "optimizer/planmain.h"
      32             : 
      33             : 
      34             : /*
      35             :  * query_planner
      36             :  *    Generate a path (that is, a simplified plan) for a basic query,
      37             :  *    which may involve joins but not any fancier features.
      38             :  *
      39             :  * Since query_planner does not handle the toplevel processing (grouping,
      40             :  * sorting, etc) it cannot select the best path by itself.  Instead, it
      41             :  * returns the RelOptInfo for the top level of joining, and the caller
      42             :  * (grouping_planner) can choose among the surviving paths for the rel.
      43             :  *
      44             :  * root describes the query to plan
      45             :  * qp_callback is a function to compute query_pathkeys once it's safe to do so
      46             :  * qp_extra is optional extra data to pass to qp_callback
      47             :  *
      48             :  * Note: the PlannerInfo node also includes a query_pathkeys field, which
      49             :  * tells query_planner the sort order that is desired in the final output
      50             :  * plan.  This value is *not* available at call time, but is computed by
      51             :  * qp_callback once we have completed merging the query's equivalence classes.
      52             :  * (We cannot construct canonical pathkeys until that's done.)
      53             :  */
      54             : RelOptInfo *
      55      302120 : query_planner(PlannerInfo *root,
      56             :               query_pathkeys_callback qp_callback, void *qp_extra)
      57             : {
      58      302120 :     Query      *parse = root->parse;
      59             :     List       *joinlist;
      60             :     RelOptInfo *final_rel;
      61             : 
      62             :     /*
      63             :      * Init planner lists to empty.
      64             :      *
      65             :      * NOTE: append_rel_list was set up by subquery_planner, so do not touch
      66             :      * here.
      67             :      */
      68      302120 :     root->join_rel_list = NIL;
      69      302120 :     root->join_rel_hash = NULL;
      70      302120 :     root->join_rel_level = NULL;
      71      302120 :     root->join_cur_level = 0;
      72      302120 :     root->canon_pathkeys = NIL;
      73      302120 :     root->left_join_clauses = NIL;
      74      302120 :     root->right_join_clauses = NIL;
      75      302120 :     root->full_join_clauses = NIL;
      76      302120 :     root->join_info_list = NIL;
      77      302120 :     root->placeholder_list = NIL;
      78      302120 :     root->fkey_list = NIL;
      79      302120 :     root->initial_rels = NIL;
      80             : 
      81             :     /*
      82             :      * Set up arrays for accessing base relations and AppendRelInfos.
      83             :      */
      84      302120 :     setup_simple_rel_arrays(root);
      85             : 
      86             :     /*
      87             :      * In the trivial case where the jointree is a single RTE_RESULT relation,
      88             :      * bypass all the rest of this function and just make a RelOptInfo and its
      89             :      * one access path.  This is worth optimizing because it applies for
      90             :      * common cases like "SELECT expression" and "INSERT ... VALUES()".
      91             :      */
      92             :     Assert(parse->jointree->fromlist != NIL);
      93      302120 :     if (list_length(parse->jointree->fromlist) == 1)
      94             :     {
      95      289060 :         Node       *jtnode = (Node *) linitial(parse->jointree->fromlist);
      96             : 
      97      289060 :         if (IsA(jtnode, RangeTblRef))
      98             :         {
      99      242152 :             int         varno = ((RangeTblRef *) jtnode)->rtindex;
     100      242152 :             RangeTblEntry *rte = root->simple_rte_array[varno];
     101             : 
     102             :             Assert(rte != NULL);
     103      242152 :             if (rte->rtekind == RTE_RESULT)
     104             :             {
     105             :                 /* Make the RelOptInfo for it directly */
     106      112032 :                 final_rel = build_simple_rel(root, varno, NULL);
     107             : 
     108             :                 /*
     109             :                  * If query allows parallelism in general, check whether the
     110             :                  * quals are parallel-restricted.  (We need not check
     111             :                  * final_rel->reltarget because it's empty at this point.
     112             :                  * Anything parallel-restricted in the query tlist will be
     113             :                  * dealt with later.)  This is normally pretty silly, because
     114             :                  * a Result-only plan would never be interesting to
     115             :                  * parallelize.  However, if force_parallel_mode is on, then
     116             :                  * we want to execute the Result in a parallel worker if
     117             :                  * possible, so we must do this.
     118             :                  */
     119      162768 :                 if (root->glob->parallelModeOK &&
     120       50736 :                     force_parallel_mode != FORCE_PARALLEL_OFF)
     121           4 :                     final_rel->consider_parallel =
     122           4 :                         is_parallel_safe(root, parse->jointree->quals);
     123             : 
     124             :                 /*
     125             :                  * The only path for it is a trivial Result path.  We cheat a
     126             :                  * bit here by using a GroupResultPath, because that way we
     127             :                  * can just jam the quals into it without preprocessing them.
     128             :                  * (But, if you hold your head at the right angle, a FROM-less
     129             :                  * SELECT is a kind of degenerate-grouping case, so it's not
     130             :                  * that much of a cheat.)
     131             :                  */
     132      112032 :                 add_path(final_rel, (Path *)
     133      112032 :                          create_group_result_path(root, final_rel,
     134      112032 :                                                   final_rel->reltarget,
     135      112032 :                                                   (List *) parse->jointree->quals));
     136             : 
     137             :                 /* Select cheapest path (pretty easy in this case...) */
     138      112032 :                 set_cheapest(final_rel);
     139             : 
     140             :                 /*
     141             :                  * We don't need to run generate_base_implied_equalities, but
     142             :                  * we do need to pretend that EC merging is complete.
     143             :                  */
     144      112032 :                 root->ec_merging_done = true;
     145             : 
     146             :                 /*
     147             :                  * We still are required to call qp_callback, in case it's
     148             :                  * something like "SELECT 2+2 ORDER BY 1".
     149             :                  */
     150      112032 :                 (*qp_callback) (root, qp_extra);
     151             : 
     152      112032 :                 return final_rel;
     153             :             }
     154             :         }
     155             :     }
     156             : 
     157             :     /*
     158             :      * Construct RelOptInfo nodes for all base relations used in the query.
     159             :      * Appendrel member relations ("other rels") will be added later.
     160             :      *
     161             :      * Note: the reason we find the baserels by searching the jointree, rather
     162             :      * than scanning the rangetable, is that the rangetable may contain RTEs
     163             :      * for rels not actively part of the query, for example views.  We don't
     164             :      * want to make RelOptInfos for them.
     165             :      */
     166      190088 :     add_base_rels_to_query(root, (Node *) parse->jointree);
     167             : 
     168             :     /*
     169             :      * Examine the targetlist and join tree, adding entries to baserel
     170             :      * targetlists for all referenced Vars, and generating PlaceHolderInfo
     171             :      * entries for all referenced PlaceHolderVars.  Restrict and join clauses
     172             :      * are added to appropriate lists belonging to the mentioned relations. We
     173             :      * also build EquivalenceClasses for provably equivalent expressions. The
     174             :      * SpecialJoinInfo list is also built to hold information about join order
     175             :      * restrictions.  Finally, we form a target joinlist for make_one_rel() to
     176             :      * work from.
     177             :      */
     178      190080 :     build_base_rel_tlists(root, root->processed_tlist);
     179             : 
     180      190080 :     find_placeholders_in_jointree(root);
     181             : 
     182      190080 :     find_lateral_references(root);
     183             : 
     184      190080 :     joinlist = deconstruct_jointree(root);
     185             : 
     186             :     /*
     187             :      * Reconsider any postponed outer-join quals now that we have built up
     188             :      * equivalence classes.  (This could result in further additions or
     189             :      * mergings of classes.)
     190             :      */
     191      190080 :     reconsider_outer_join_clauses(root);
     192             : 
     193             :     /*
     194             :      * If we formed any equivalence classes, generate additional restriction
     195             :      * clauses as appropriate.  (Implied join clauses are formed on-the-fly
     196             :      * later.)
     197             :      */
     198      190080 :     generate_base_implied_equalities(root);
     199             : 
     200             :     /*
     201             :      * We have completed merging equivalence sets, so it's now possible to
     202             :      * generate pathkeys in canonical form; so compute query_pathkeys and
     203             :      * other pathkeys fields in PlannerInfo.
     204             :      */
     205      190080 :     (*qp_callback) (root, qp_extra);
     206             : 
     207             :     /*
     208             :      * Examine any "placeholder" expressions generated during subquery pullup.
     209             :      * Make sure that the Vars they need are marked as needed at the relevant
     210             :      * join level.  This must be done before join removal because it might
     211             :      * cause Vars or placeholders to be needed above a join when they weren't
     212             :      * so marked before.
     213             :      */
     214      190080 :     fix_placeholder_input_needed_levels(root);
     215             : 
     216             :     /*
     217             :      * Remove any useless outer joins.  Ideally this would be done during
     218             :      * jointree preprocessing, but the necessary information isn't available
     219             :      * until we've built baserel data structures and classified qual clauses.
     220             :      */
     221      190080 :     joinlist = remove_useless_joins(root, joinlist);
     222             : 
     223             :     /*
     224             :      * Also, reduce any semijoins with unique inner rels to plain inner joins.
     225             :      * Likewise, this can't be done until now for lack of needed info.
     226             :      */
     227      190080 :     reduce_unique_semijoins(root);
     228             : 
     229             :     /*
     230             :      * Now distribute "placeholders" to base rels as needed.  This has to be
     231             :      * done after join removal because removal could change whether a
     232             :      * placeholder is evaluable at a base rel.
     233             :      */
     234      190080 :     add_placeholders_to_base_rels(root);
     235             : 
     236             :     /*
     237             :      * Construct the lateral reference sets now that we have finalized
     238             :      * PlaceHolderVar eval levels.
     239             :      */
     240      190080 :     create_lateral_join_info(root);
     241             : 
     242             :     /*
     243             :      * Match foreign keys to equivalence classes and join quals.  This must be
     244             :      * done after finalizing equivalence classes, and it's useful to wait till
     245             :      * after join removal so that we can skip processing foreign keys
     246             :      * involving removed relations.
     247             :      */
     248      190080 :     match_foreign_keys_to_quals(root);
     249             : 
     250             :     /*
     251             :      * Look for join OR clauses that we can extract single-relation
     252             :      * restriction OR clauses from.
     253             :      */
     254      190080 :     extract_restriction_or_clauses(root);
     255             : 
     256             :     /*
     257             :      * Now expand appendrels by adding "otherrels" for their children.  We
     258             :      * delay this to the end so that we have as much information as possible
     259             :      * available for each baserel, including all restriction clauses.  That
     260             :      * let us prune away partitions that don't satisfy a restriction clause.
     261             :      * Also note that some information such as lateral_relids is propagated
     262             :      * from baserels to otherrels here, so we must have computed it already.
     263             :      */
     264      190080 :     add_other_rels_to_query(root);
     265             : 
     266             :     /*
     267             :      * Ready to do the primary planning.
     268             :      */
     269      190078 :     final_rel = make_one_rel(root, joinlist);
     270             : 
     271             :     /* Check that we got at least one usable path */
     272      380156 :     if (!final_rel || !final_rel->cheapest_total_path ||
     273      190078 :         final_rel->cheapest_total_path->param_info != NULL)
     274           0 :         elog(ERROR, "failed to construct the join relation");
     275             : 
     276      190078 :     return final_rel;
     277             : }

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