bzr commit into mysql-6.0-codebase-bugfixing branch (tor.didriksen:3830) Bug#52068

[Tor Didriksen]

#At file:///export/home/didrik/mysqldev-6.0-codebase/6.0-codebase-bf-review52068/ based on revid:tor.didriksen@stripped

 3830 Tor Didriksen	2010-03-17
      comments/questions on patch for bug#52068

    modified:
      sql/sql_select.cc
=== modified file 'sql/sql_select.cc'
--- a/sql/sql_select.cc	2010-03-17 09:59:35 +0000
+++ b/sql/sql_select.cc	2010-03-17 14:27:53 +0000
@@ -1148,16 +1148,17 @@ static bool sj_table_is_included(JOIN *j
                      be used.
 
   DESCRIPTION
-    Setup the strategies to eliminate semi-join duplicates. ATM there are 4
-    strategies:
+    Setup the strategies to eliminate semi-join duplicates.
+    At the moment there are 5 strategies:
 
     1. DuplicateWeedout (use of temptable to remove duplicates based on rowids
                          of row combinations)
     2. FirstMatch (pick only the 1st matching row combination of inner tables)
     3. LooseScan (scanning the sj-inner table in a way that groups duplicates
                   together and picking the 1st one)
-    4. SJ-Materialization.
-    
+    4. MaterializeLookup
+    5. MaterializeScan
+
     The join order has "duplicate-generating ranges", and every range is
     served by one strategy or a combination of FirstMatch with with some
     other strategy.
@@ -1232,7 +1233,7 @@ static bool sj_table_is_included(JOIN *j
       (2) - The handled range, which may contain only inner tables.
             The inner tables are materialized in a temporary table that is
             later used as a lookup structure for the outer correlated tables.
-      (3) - The suffix of outer non-correlated tables.
+      (3) - The suffix of non-correlated tables.
 
     MaterializeScan strategy
     ~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -1241,7 +1242,7 @@ static bool sj_table_is_included(JOIN *j
       +---+  +==========+  +-----+
        (1)        (2)        (3)
 
-      (1) - Prefix of outer non-correlated tables.
+      (1) - Prefix of non-correlated tables.
 
       (2) - The handled range, which may contain only inner tables.
             The inner tables are materialized in a temporary table which is
@@ -7232,7 +7233,7 @@ optimize_straight_join(JOIN *join, table
            is returned. This is a purely heuristic decision.
 */
 
-static uint
+static int
 allows_semijoin_materialization(const JOIN *join, table_map remaining_tables,
                                 const JOIN_TAB *tab, uint idx)
 {
@@ -7241,28 +7242,31 @@ allows_semijoin_materialization(const JO
     1. We're in a semi-join nest that can be run with SJ-materialization
     2. All the tables from the subquery are in the prefix
   */
-  TABLE_LIST *emb_sj_nest= tab->emb_sj_nest;
+  const TABLE_LIST *emb_sj_nest= tab->emb_sj_nest;
   if (!emb_sj_nest ||
       !emb_sj_nest->sj_mat_info ||
       remaining_tables & emb_sj_nest->sj_inner_tables)
     return SJ_OPT_NONE;
+
   /* 
     Walk back and check if all immediately preceding tables are from
     this semi-join.
   */
-  uint n_tables= my_count_bits(emb_sj_nest->sj_inner_tables);
+  const uint n_tables= my_count_bits(emb_sj_nest->sj_inner_tables);
   for (uint i= 1; i < n_tables ; i++)
   {
     if (join->positions[idx - i].table->emb_sj_nest != emb_sj_nest)
       return SJ_OPT_NONE;
   }
+
   /*
     Disallow any plan that has dependent outer tables both in the prefix
     part and the suffix part of the table order.
   */
-  if ((remaining_tables & emb_sj_nest->nested_join->sj_depends_on) &&
-      (emb_sj_nest->nested_join->sj_depends_on & ~remaining_tables))
+  if (( remaining_tables & emb_sj_nest->nested_join->sj_depends_on) &&
+      (~remaining_tables & emb_sj_nest->nested_join->sj_depends_on))
     return SJ_OPT_NONE;
+
   /*
     Must use MaterializeScan strategy if there are outer correlated tables
     among the remaining tables.
@@ -7271,11 +7275,9 @@ allows_semijoin_materialization(const JO
   {
     if (!emb_sj_nest->sj_subq_pred->sjm_scan_allowed)
       return SJ_OPT_NONE;
-    else
-      return SJ_OPT_MATERIALIZE_SCAN;
+    return SJ_OPT_MATERIALIZE_SCAN;
   }
-  else
-    return SJ_OPT_MATERIALIZE_LOOKUP;
+  return SJ_OPT_MATERIALIZE_LOOKUP;
 }
 
 
@@ -13454,8 +13456,8 @@ void advance_sj_state(JOIN *join, table_
   join->cur_dups_producing_tables &= ~handled_by_fm_or_ls;
 
   /* 4. MaterializationLookup and MaterializationScan strategy handler */
-  uint sjm_strategy= allows_semijoin_materialization(join, remaining_tables,
-                                                     new_join_tab, idx);
+  const int sjm_strategy=
+    allows_semijoin_materialization(join, remaining_tables, new_join_tab, idx);
   if (sjm_strategy != SJ_OPT_NONE)
   {
     SJ_MATERIALIZATION_INFO *mat_info= emb_sj_nest->sj_mat_info;


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