MDEV-406: ANALYZE $stmt: get ANALYZE work for subqueries

- "ANALYZE $stmt" should discard select's output, but it should still
  evaluate the output columns (otherwise, subqueries in select list
  are not executed)
- SHOW EXPLAIN's code practice of calling JOIN::save_explain_data()
  after JOIN::exec() is disastrous for ANALYZE, because it resets
  all counters after the first execution. It is stopped
  = "Late" test_if_skip_sort_order() calls explicitly update their part
    of the query plan.
  = Also, I had to rewrite I_S optimization to actually have optimization
    and execution stages.

mysql-test/r/analyze_stmt.result

@@ -61,3 +61,17 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	r_rows	filtered	r_f
 NULL	UNION RESULT	<union1,2>	ALL	NULL	NULL	NULL	NULL	NULL	5	NULL	NULL	
 drop table t1;
 drop table t0;
+# 
+# Try a subquery.
+# 
+create table t0 (a int, b int);
+insert into t0 values
+(0,0),(1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7),(8,8),(9,9);
+create table t1 (a int, b int);
+insert into t1 values (1,1),(2,2),(3,3);
+# See .test file for the right values of r_rows and r_filtered.
+analyze select a, a in (select t0.b from t0 where t0.b+1=t1.b+1) from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	r_rows	filtered	r_filtered	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	3	100.00	100.00	
+2	DEPENDENT SUBQUERY	t0	ALL	NULL	NULL	NULL	NULL	10	3	100.00	33.33	Using where
+drop table t0,t1;

mysql-test/r/show_explain.result

@@ -641,7 +641,7 @@ set debug_dbug='+d,show_explain_probe_join_exec_start';
 SHOW INDEX FROM t1;
 show explain for $thr2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	STATISTICS	ALL	NULL	NULL	NULL	NULL	NULL	Skip_open_table; Scanned all databases
+1	SIMPLE	STATISTICS	ALL	NULL	TABLE_SCHEMA,TABLE_NAME	NULL	NULL	NULL	Open_full_table; Scanned 0 databases
 Warnings:
 Note	1003	SHOW INDEX FROM t1
 Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment	Index_comment

mysql-test/t/analyze_stmt.test

@@ -34,5 +34,29 @@ insert into t1 select a,a from t0;
 analyze (select * from t1 A where a<5) union (select * from t1 B where a in (5,6));
 analyze (select * from t1 A where a<5) union (select * from t1 B where a in (1,2));
 drop table t1;
-
 drop table t0;
+
+--echo # 
+--echo # Try a subquery.
+--echo # 
+create table t0 (a int, b int);
+insert into t0 values
+  (0,0),(1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7),(8,8),(9,9);
+
+create table t1 (a int, b int);
+insert into t1 values (1,1),(2,2),(3,3);
+
+#
+#   t1      t0
+#   a=1     (0,1)       2 rows
+#   a=2     (0,1,2)     3 rows
+#   a=3     (0,1,2,3)   4 rows
+#
+#  TOTAL    TOTAL= 9 rows.  3 executions, avg=3 rows.
+#  WHERE is satisfied for 1 row per query, which gives filtered=33.3
+
+--echo # See .test file for the right values of r_rows and r_filtered.
+analyze select a, a in (select t0.b from t0 where t0.b+1=t1.b+1) from t1;
+
+drop table t0,t1;
+

sql/protocol.h

@@ -210,6 +210,42 @@ public:
   virtual enum enum_protocol_type type() { return PROTOCOL_BINARY; };
 };
 
+
+/*
+  A helper for "ANALYZE $stmt" which looks a real network procotol but doesn't
+  write results to the network.
+
+  At first glance, class select_send looks like a more appropriate place to
+  implement the "write nothing" hook. This is not true, because
+    - we need to evaluate the value of every item, and do it the way
+      select_send does it (i.e. call item->val_int() or val_real() or...)
+    - select_send::send_data() has some other code, like telling the storage
+      engine that the row can be unlocked. We want to keep that also.
+  as a result, "ANALYZE $stmt" uses a select_send_analyze which still uses 
+  select_send::send_data() & co., and also uses  Protocol_discard object.
+*/
+
+class Protocol_discard : public Protocol_text
+{
+public:
+  Protocol_discard(THD *thd_arg) : Protocol_text(thd_arg) {}
+  /* The real writing is done only in write() */
+  virtual bool write() { return 0; }
+  virtual bool send_result_set_metadata(List<Item> *list, uint flags)
+  {
+    // Don't pas Protocol::SEND_NUM_ROWS | Protocol::SEND_EOF flags 
+    return Protocol_text::send_result_set_metadata(list, 0);
+  }
+
+  // send_error is intentionally not overloaded.
+  virtual bool send_eof(uint server_status, uint statement_warn_count)
+  {
+    return 0;
+  }
+
+};
+
+
 void send_warning(THD *thd, uint sql_errno, const char *err=0);
 bool net_send_error(THD *thd, uint sql_errno, const char *err,
                     const char* sqlstate);

sql/sql_class.h

@@ -3959,19 +3959,21 @@ public:
   virtual void cleanup();
 };
 
+
+/*
+  We need this class, because select_send::send_eof() will call ::my_eof.
+
+  See also class Protocol_discard.
+*/
+
 class select_send_analyze : public select_send
 {
-bool discard_data;
   bool send_result_set_metadata(List<Item> &list, uint flags) { return 0; }
-  /* 
-    ANALYZE-todo: we should call val_int() (or val_str() or whatever) to
-    compute the columns. If we don't, it's not full execution.
-  */
-  int send_data(List<Item> &items) { return 0; }
   bool send_eof() { return 0; }
   void abort_result_set() {}
 };
 
+
 class select_to_file :public select_result_interceptor {
 protected:
   sql_exchange *exchange;

sql/sql_explain.cc

@@ -345,6 +345,13 @@ int Explain_node::print_explain_for_children(Explain_query *query,
 }
 
 
+void Explain_select::replace_table(uint idx, Explain_table_access *new_tab)
+{
+  delete join_tabs[idx];
+  join_tabs[idx]= new_tab;
+}
+
+
 Explain_select::~Explain_select()
 {
   if (join_tabs)

sql/sql_explain.h

@@ -130,6 +130,12 @@ public:
     return false;
   }
   
+  /*
+    This is used to save the results of "late" test_if_skip_sort_order() calls
+    that are made from JOIN::exec
+  */
+  void replace_table(uint idx, Explain_table_access *new_tab);
+
 public:
   int select_id;
   const char *select_type;

sql/sql_parse.cc

@@ -5260,10 +5260,13 @@ static bool execute_sqlcom_select(THD *thd, TABLE_LIST *all_tables)
     {
       //psergey-todo: ANALYZE should hook in here...
       select_result *save_result;
+      Protocol *save_protocol;
       if (lex->analyze_stmt)
       {
         save_result= result;
         result= new select_send_analyze();
+        save_protocol= thd->protocol;
+        thd->protocol= new Protocol_discard(thd);
       }
       else
       {
@@ -5280,6 +5283,7 @@ static bool execute_sqlcom_select(THD *thd, TABLE_LIST *all_tables)
         result= save_result;
         if (!result && !(result= new select_send()))
           return 1;
+        thd->protocol= save_protocol;
         thd->lex->explain->send_explain(thd);
 
         if (result != lex->result)

sql/sql_select.cc

@@ -1873,6 +1873,9 @@ TODO: make view to decide if it is possible to write to WHERE directly or make S
     }
   }
 
+  if ((select_lex->options & OPTION_SCHEMA_TABLE))
+    optimize_schema_tables_reads(this);
+
   tmp_having= having;
   if (select_options & SELECT_DESCRIBE)
   {
@@ -1919,6 +1922,7 @@ setup_subq_exit:
   error= 0;
 
 derived_exit:
+
   select_lex->mark_const_derived(zero_result_cause);
   DBUG_RETURN(0);
 }
@@ -2059,6 +2063,7 @@ int JOIN::init_execution()
                                     &join_tab[const_tables].table->
                                       keys_in_use_for_order_by))
 	  order=0;
+        join_tab[const_tables].update_explain_data(const_tables);
       }
     }
 
@@ -2383,10 +2388,12 @@ void JOIN::exec()
 
   if (!exec_saved_explain)
   {
+#if 0
     save_explain_data(thd->lex->explain, true /* can overwrite */,
                       need_tmp,
                       order != 0 && !skip_sort_order,
                       select_distinct);
+#endif    
     exec_saved_explain= true;
   }
 
@@ -2564,15 +2571,19 @@ void JOIN::exec_inner()
       simple_order= simple_group;
       skip_sort_order= 0;
     }
+    bool made_call= false;
     if (order && 
         (order != group_list || !(select_options & SELECT_BIG_RESULT)) &&
 	(const_tables == table_count ||
  	 ((simple_order || skip_sort_order) &&
-	  test_if_skip_sort_order(&join_tab[const_tables], order,
+	  (made_call=true) &&
+          test_if_skip_sort_order(&join_tab[const_tables], order,
 				  select_limit, 0, 
                                   &join_tab[const_tables].table->
                                     keys_in_use_for_query))))
       order=0;
+    if (made_call)
+      join_tab[const_tables].update_explain_data(const_tables);
     having= tmp_having;
     select_describe(this, need_tmp,
 		    order != 0 && !skip_sort_order,
@@ -20535,7 +20546,12 @@ create_sort_index(THD *thd, JOIN *join, ORDER *order,
       test_if_skip_sort_order(tab,order,select_limit,0, 
                               is_order_by ?  &table->keys_in_use_for_order_by :
                               &table->keys_in_use_for_group_by))
+  {
+    tab->update_explain_data(join->const_tables);
     DBUG_RETURN(0);
+  }
+  tab->update_explain_data(join->const_tables);
+
   for (ORDER *ord= join->order; ord; ord= ord->next)
     length++;
   if (!(join->sortorder= 
@@ -23248,6 +23264,416 @@ void append_possible_keys(String *str, TABLE *table, key_map possible_keys)
   }
 }
 
+// TODO: this function is only applicable for the first non-const optimization
+// join tab. 
+void JOIN_TAB::update_explain_data(uint idx)
+{
+  if (this == first_breadth_first_tab(join, WALK_OPTIMIZATION_TABS) &&
+      join->select_lex->select_number != INT_MAX &&
+      join->select_lex->select_number != UINT_MAX)
+  {
+    Explain_table_access *eta= new Explain_table_access();
+    JOIN_TAB* const first_top_tab= first_breadth_first_tab(join, WALK_OPTIMIZATION_TABS);
+    save_explain_data(eta, join->const_table_map, join->select_distinct, first_top_tab);
+
+    Explain_select *sel= join->thd->lex->explain->get_select(join->select_lex->select_number);
+    sel->replace_table(idx, eta);
+  }
+}
+
+
+void JOIN_TAB::save_explain_data(Explain_table_access *eta, table_map prefix_tables, 
+                                 bool distinct, JOIN_TAB *first_top_tab)
+{
+  int quick_type;
+  const CHARSET_INFO *cs= system_charset_info;
+
+  JOIN_TAB *tab= this;
+  THD *thd=join->thd;
+
+  TABLE *table=tab->table;
+  TABLE_LIST *table_list= tab->table->pos_in_table_list;
+  char buff4[512];
+  my_bool key_read;
+  char table_name_buffer[SAFE_NAME_LEN];
+  String tmp4(buff4,sizeof(buff4),cs);
+  KEY *key_info= 0;
+  uint key_len= 0;
+  tmp4.length(0);
+  quick_type= -1;
+  QUICK_SELECT_I *quick= NULL;
+
+  eta->key.set(thd->mem_root, NULL, (uint)-1);
+  eta->quick_info= NULL;
+  
+  tab->tracker= &eta->tracker;
+  
+  /* id */
+  if (tab->bush_root_tab)
+  {
+    JOIN_TAB *first_sibling= tab->bush_root_tab->bush_children->start;
+    eta->sjm_nest_select_id= first_sibling->emb_sj_nest->sj_subq_pred->get_identifier();
+  }
+  else
+    eta->sjm_nest_select_id= 0;
+
+  /* select_type is kept in Explain_select */
+
+  /* table */
+  if (table->derived_select_number)
+  {
+    /* Derived table name generation */
+    int len= my_snprintf(table_name_buffer, sizeof(table_name_buffer)-1,
+                         "<derived%u>",
+                         table->derived_select_number);
+    eta->table_name.copy(table_name_buffer, len, cs);
+  }
+  else if (tab->bush_children)
+  {
+    JOIN_TAB *ctab= tab->bush_children->start;
+    /* table */
+    int len= my_snprintf(table_name_buffer, 
+                         sizeof(table_name_buffer)-1,
+                         "<subquery%d>", 
+                         ctab->emb_sj_nest->sj_subq_pred->get_identifier());
+    eta->table_name.copy(table_name_buffer, len, cs);
+  }
+  else
+  {
+    TABLE_LIST *real_table= table->pos_in_table_list;
+    eta->table_name.copy(real_table->alias, strlen(real_table->alias), cs);
+  }
+
+  /* "partitions" column */
+  {
+#ifdef WITH_PARTITION_STORAGE_ENGINE
+    partition_info *part_info;
+    if (!table->derived_select_number && 
+        (part_info= table->part_info))
+    {          
+      make_used_partitions_str(part_info, &eta->used_partitions);
+      eta->used_partitions_set= true;
+    }
+    else
+      eta->used_partitions_set= false;
+#else
+    /* just produce empty column if partitioning is not compiled in */
+    eta->used_partitions_set= false;
+#endif
+  }
+
+  /* "type" column */
+  enum join_type tab_type= tab->type;
+  if ((tab->type == JT_ALL || tab->type == JT_HASH) &&
+       tab->select && tab->select->quick && tab->use_quick != 2)
+  {
+    quick= tab->select->quick;
+    quick_type= tab->select->quick->get_type();
+    if ((quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE) ||
+        (quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_INTERSECT) ||
+        (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT) ||
+        (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_UNION))
+      tab_type= tab->type == JT_ALL ? JT_INDEX_MERGE : JT_HASH_INDEX_MERGE;
+    else
+      tab_type= tab->type == JT_ALL ? JT_RANGE : JT_HASH_RANGE;
+  }
+  eta->type= tab_type;
+
+  /* Build "possible_keys" value */
+  append_possible_keys(&eta->possible_keys_str, table, tab->keys);
+
+  /* Build "key", "key_len", and "ref" */
+  if (tab_type == JT_NEXT)
+  {
+    key_info= table->key_info+tab->index;
+    key_len= key_info->key_length;
+  }
+  else if (tab->ref.key_parts)
+  {
+    key_info= tab->get_keyinfo_by_key_no(tab->ref.key);
+    key_len= tab->ref.key_length;
+  }
+  
+  /*
+    In STRAIGHT_JOIN queries, there can be join tabs with JT_CONST type
+    that still have quick selects.
+  */
+  if (tab->select && tab->select->quick && tab_type != JT_CONST)
+  {
+    eta->quick_info= tab->select->quick->get_explain(thd->mem_root);
+  }
+
+  if (key_info) /* 'index' or 'ref' access */
+  {
+    eta->key.set(thd->mem_root, key_info->name, key_len);
+
+    if (tab->ref.key_parts && tab_type != JT_FT)
+    {
+      store_key **ref=tab->ref.key_copy;
+      for (uint kp= 0; kp < tab->ref.key_parts; kp++)
+      {
+        if (tmp4.length())
+          tmp4.append(',');
+
+        if ((key_part_map(1) << kp) & tab->ref.const_ref_part_map)
+          tmp4.append("const");
+        else
+        {
+          tmp4.append((*ref)->name(), strlen((*ref)->name()), cs);
+          ref++;
+        }
+      }
+    }
+  }
+
+  if (tab_type == JT_HASH_NEXT) /* full index scan + hash join */
+  {
+    eta->hash_next_key.set(thd->mem_root, 
+                           table->key_info[tab->index].name, 
+                           table->key_info[tab->index].key_length);
+  }
+
+  if (key_info)
+  {
+    if (key_info && tab_type != JT_NEXT)
+    {
+      eta->ref.copy(tmp4);
+      eta->ref_set= true;
+    }
+    else
+      eta->ref_set= false;
+  }
+  else
+  {
+    if (table_list && /* SJM bushes don't have table_list */
+        table_list->schema_table &&
+        table_list->schema_table->i_s_requested_object & OPTIMIZE_I_S_TABLE)
+    {
+      IS_table_read_plan *is_table_read_plan= table_list->is_table_read_plan;
+      const char *tmp_buff;
+      int f_idx;
+      StringBuffer<64> key_name_buf;
+      if (is_table_read_plan->has_db_lookup_value())
+      {
+        /* The "key" has the name of the column referring to the database */
+        f_idx= table_list->schema_table->idx_field1;
+        tmp_buff= table_list->schema_table->fields_info[f_idx].field_name;
+        key_name_buf.append(tmp_buff, strlen(tmp_buff), cs);
+      }          
+      if (is_table_read_plan->has_table_lookup_value())
+      {
+        if (is_table_read_plan->has_db_lookup_value())
+          key_name_buf.append(',');
+
+        f_idx= table_list->schema_table->idx_field2;
+        tmp_buff= table_list->schema_table->fields_info[f_idx].field_name;
+        key_name_buf.append(tmp_buff, strlen(tmp_buff), cs);
+      }
+
+      if (key_name_buf.length())
+        eta->key.set(thd->mem_root, key_name_buf.c_ptr_safe(), -1);
+    }
+    eta->ref_set= false;
+  }
+  
+  /* "rows" */
+  if (table_list /* SJM bushes don't have table_list */ &&
+      table_list->schema_table)
+  {
+    /* I_S tables have rows=extra=NULL */
+    eta->rows_set= false;
+    eta->filtered_set= false;
+  }
+  else
+  {
+    double examined_rows= tab->get_examined_rows();
+
+    eta->rows_set= true;
+    eta->rows= (ha_rows) examined_rows;
+
+    /* "filtered"  */
+    float f= 0.0; 
+    if (examined_rows)
+    {
+      double pushdown_cond_selectivity= tab->cond_selectivity;	      
+      if (pushdown_cond_selectivity == 1.0)
+        f= (float) (100.0 * tab->records_read / examined_rows);
+      else
+        f= (float) (100.0 * pushdown_cond_selectivity);
+    }
+    set_if_smaller(f, 100.0);
+    eta->filtered_set= true;
+    eta->filtered= f;
+  }
+
+  /* Build "Extra" field and save it */
+  key_read=table->key_read;
+  if ((tab_type == JT_NEXT || tab_type == JT_CONST) &&
+      table->covering_keys.is_set(tab->index))
+    key_read=1;
+  if (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT &&
+      !((QUICK_ROR_INTERSECT_SELECT*)quick)->need_to_fetch_row)
+    key_read=1;
+    
+  if (tab->info)
+  {
+    eta->push_extra(tab->info);
+  }
+  else if (tab->packed_info & TAB_INFO_HAVE_VALUE)
+  {
+    if (tab->packed_info & TAB_INFO_USING_INDEX)
+      eta->push_extra(ET_USING_INDEX);
+    if (tab->packed_info & TAB_INFO_USING_WHERE)
+      eta->push_extra(ET_USING_WHERE);
+    if (tab->packed_info & TAB_INFO_FULL_SCAN_ON_NULL)
+      eta->push_extra(ET_FULL_SCAN_ON_NULL_KEY);
+  }
+  else
+  {
+    uint keyno= MAX_KEY;
+    if (tab->ref.key_parts)
+      keyno= tab->ref.key;
+    else if (tab->select && quick)
+      keyno = quick->index;
+
+    if (keyno != MAX_KEY && keyno == table->file->pushed_idx_cond_keyno &&
+        table->file->pushed_idx_cond)
+      eta->push_extra(ET_USING_INDEX_CONDITION);
+    else if (tab->cache_idx_cond)
+      eta->push_extra(ET_USING_INDEX_CONDITION_BKA);
+
+    if (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_UNION || 
+        quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT ||
+        quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_INTERSECT ||
+        quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE)
+    {
+      eta->push_extra(ET_USING);
+    }
+    if (tab->select)
+    {
+      if (tab->use_quick == 2)
+      {
+        eta->push_extra(ET_RANGE_CHECKED_FOR_EACH_RECORD);
+        eta->range_checked_map= tab->keys;
+      }
+      else if (tab->select->cond ||
+               (tab->cache_select && tab->cache_select->cond))
+      {
+        const COND *pushed_cond= tab->table->file->pushed_cond;
+
+        if (((thd->variables.optimizer_switch &
+             OPTIMIZER_SWITCH_ENGINE_CONDITION_PUSHDOWN) ||
+             (tab->table->file->ha_table_flags() &
+              HA_MUST_USE_TABLE_CONDITION_PUSHDOWN)) &&
+            pushed_cond)
+        {
+          eta->push_extra(ET_USING_WHERE_WITH_PUSHED_CONDITION);
+          /*
+          psergey-todo: what to do? This was useful with NDB only.
+
+          if (explain_flags & DESCRIBE_EXTENDED)
+          {
+            extra.append(STRING_WITH_LEN(": "));
+            ((COND *)pushed_cond)->print(&extra, QT_ORDINARY);
+          }
+          */
+        }
+        else
+          eta->push_extra(ET_USING_WHERE);
+      }
+    }
+    if (table_list /* SJM bushes don't have table_list */ &&
+        table_list->schema_table &&
+        table_list->schema_table->i_s_requested_object & OPTIMIZE_I_S_TABLE)
+    {
+      if (!table_list->table_open_method)
+        eta->push_extra(ET_SKIP_OPEN_TABLE);
+      else if (table_list->table_open_method == OPEN_FRM_ONLY)
+        eta->push_extra(ET_OPEN_FRM_ONLY);
+      else
+        eta->push_extra(ET_OPEN_FULL_TABLE);
+      /* psergey-note: the following has a bug.*/
+      if (table_list->is_table_read_plan->has_db_lookup_value() &&
+          table_list->is_table_read_plan->has_table_lookup_value())
+        eta->push_extra(ET_SCANNED_0_DATABASES);
+      else if (table_list->is_table_read_plan->has_db_lookup_value() ||
+               table_list->is_table_read_plan->has_table_lookup_value())
+        eta->push_extra(ET_SCANNED_1_DATABASE);
+      else
+        eta->push_extra(ET_SCANNED_ALL_DATABASES);
+    }
+    if (key_read)
+    {
+      if (quick_type == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
+      {
+        QUICK_GROUP_MIN_MAX_SELECT *qgs= 
+          (QUICK_GROUP_MIN_MAX_SELECT *) tab->select->quick;
+        eta->push_extra(ET_USING_INDEX_FOR_GROUP_BY);
+        eta->loose_scan_is_scanning= qgs->loose_scan_is_scanning();
+      }
+      else
+        eta->push_extra(ET_USING_INDEX);
+    }
+    if (table->reginfo.not_exists_optimize)
+      eta->push_extra(ET_NOT_EXISTS);
+
+    if (quick_type == QUICK_SELECT_I::QS_TYPE_RANGE)
+    {
+      explain_append_mrr_info((QUICK_RANGE_SELECT*)(tab->select->quick),
+                              &eta->mrr_type);
+      if (eta->mrr_type.length() > 0)
+        eta->push_extra(ET_USING_MRR);
+    }
+
+    if (distinct & test_all_bits(prefix_tables, join->select_list_used_tables))
+      eta->push_extra(ET_DISTINCT);
+    if (tab->loosescan_match_tab)
+    {
+      eta->push_extra(ET_LOOSESCAN);
+    }
+
+    if (tab->first_weedout_table)
+      eta->push_extra(ET_START_TEMPORARY);
+    if (tab->check_weed_out_table)
+      eta->push_extra(ET_END_TEMPORARY);
+    else if (tab->do_firstmatch)
+    {
+      if (tab->do_firstmatch == /*join->join_tab*/ first_top_tab - 1)
+        eta->push_extra(ET_FIRST_MATCH);
+      else
+      {
+        eta->push_extra(ET_FIRST_MATCH);
+        TABLE *prev_table=tab->do_firstmatch->table;
+        if (prev_table->derived_select_number)
+        {
+          char namebuf[NAME_LEN];
+          /* Derived table name generation */
+          int len= my_snprintf(namebuf, sizeof(namebuf)-1,
+                               "<derived%u>",
+                               prev_table->derived_select_number);
+          eta->firstmatch_table_name.append(namebuf, len);
+        }
+        else
+          eta->firstmatch_table_name.append(prev_table->pos_in_table_list->alias);
+      }
+    }
+
+    for (uint part= 0; part < tab->ref.key_parts; part++)
+    {
+      if (tab->ref.cond_guards[part])
+      {
+        eta->push_extra(ET_FULL_SCAN_ON_NULL_KEY);
+        break;
+      }
+    }
+
+    if (tab->cache)
+    {
+      eta->push_extra(ET_USING_JOIN_BUFFER);
+      tab->cache->save_explain_data(&eta->bka_type);
+    }
+  }
+}
 
 /*
   Save Query Plan Footprint
@@ -23262,9 +23688,6 @@ int JOIN::save_explain_data_intern(Explain_query *output, bool need_tmp_table,
 {
   Explain_node *explain_node;
   JOIN *join= this; /* Legacy: this code used to be a non-member function */
-  THD *thd=join->thd;
-  const CHARSET_INFO *cs= system_charset_info;
-  int quick_type;
   int error= 0;
   DBUG_ENTER("JOIN::save_explain_data_intern");
   DBUG_PRINT("info", ("Select 0x%lx, type %s, message %s",
@@ -23305,27 +23728,9 @@ int JOIN::save_explain_data_intern(Explain_query *output, bool need_tmp_table,
     for (JOIN_TAB *tab= first_breadth_first_tab(join, WALK_OPTIMIZATION_TABS); tab;
          tab= next_breadth_first_tab(join, WALK_OPTIMIZATION_TABS, tab))
     {
-      uint select_id;
-      if (tab->bush_root_tab)
-      {
-        JOIN_TAB *first_sibling= tab->bush_root_tab->bush_children->start;
-        select_id= first_sibling->emb_sj_nest->sj_subq_pred->get_identifier();
-      }
-      else
-        select_id= join->select_lex->select_number;
       
-      TABLE *table=tab->table;
-      TABLE_LIST *table_list= tab->table->pos_in_table_list;
-      char buff4[512];
-      my_bool key_read;
-      char table_name_buffer[SAFE_NAME_LEN];
-      String tmp4(buff4,sizeof(buff4),cs);
-      KEY *key_info= 0;
-      uint key_len= 0;
-      tmp4.length(0);
-      quick_type= -1;
-      QUICK_SELECT_I *quick= NULL;
       JOIN_TAB *saved_join_tab= NULL;
+      TABLE *table=tab->table;
 
       /* Don't show eliminated tables */
       if (table->map & join->eliminated_tables)
@@ -23343,383 +23748,18 @@ int JOIN::save_explain_data_intern(Explain_query *output, bool need_tmp_table,
 
       Explain_table_access *eta= new (output->mem_root) Explain_table_access;
       xpl_sel->add_table(eta);
-      eta->key.set(thd->mem_root, NULL, (uint)-1);
-      eta->quick_info= NULL;
 
-      tab->tracker= &eta->tracker;
+      tab->save_explain_data(eta, used_tables, distinct, first_top_tab);
 
-      /* id */
+      if (need_tmp_table)
-      if (tab->bush_root_tab)
-        eta->sjm_nest_select_id= select_id;
-      else
-        eta->sjm_nest_select_id= 0;
-
-      /* select_type */
-      xpl_sel->select_type= join->select_lex->type;
-
-      /* table */
-      if (table->derived_select_number)
       {
-	/* Derived table name generation */
+        need_tmp_table=0;
-	int len= my_snprintf(table_name_buffer, sizeof(table_name_buffer)-1,
+        xpl_sel->using_temporary= true;
-			     "<derived%u>",
-			     table->derived_select_number);
-	eta->table_name.copy(table_name_buffer, len, cs);
       }
-      else if (tab->bush_children)
+      if (need_order)
       {
-        JOIN_TAB *ctab= tab->bush_children->start;
+        need_order=0;
-        /* table */
+        xpl_sel->using_filesort= true;
-        int len= my_snprintf(table_name_buffer, 
-                             sizeof(table_name_buffer)-1,
-                             "<subquery%d>", 
-                             ctab->emb_sj_nest->sj_subq_pred->get_identifier());
-	eta->table_name.copy(table_name_buffer, len, cs);
-      }
-      else
-      {
-        TABLE_LIST *real_table= table->pos_in_table_list;
-	eta->table_name.copy(real_table->alias, strlen(real_table->alias), cs);
-      }
-
-      /* "partitions" column */
-      {
-#ifdef WITH_PARTITION_STORAGE_ENGINE
-        partition_info *part_info;
-        if (!table->derived_select_number && 
-            (part_info= table->part_info))
-        {          
-          make_used_partitions_str(part_info, &eta->used_partitions);
-          eta->used_partitions_set= true;
-        }
-        else
-          eta->used_partitions_set= false;
-#else
-        /* just produce empty column if partitioning is not compiled in */
-        eta->used_partitions_set= false;
-#endif
-      }
-
-      /* "type" column */
-      enum join_type tab_type= tab->type;
-      if ((tab->type == JT_ALL || tab->type == JT_HASH) &&
-           tab->select && tab->select->quick && tab->use_quick != 2)
-      {
-        quick= tab->select->quick;
-        quick_type= tab->select->quick->get_type();
-        if ((quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE) ||
-            (quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_INTERSECT) ||
-            (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT) ||
-            (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_UNION))
-          tab_type= tab->type == JT_ALL ? JT_INDEX_MERGE : JT_HASH_INDEX_MERGE;
-        else
-	  tab_type= tab->type == JT_ALL ? JT_RANGE : JT_HASH_RANGE;
-      }
-      eta->type= tab_type;
-
-      /* Build "possible_keys" value */
-      append_possible_keys(&eta->possible_keys_str, table, tab->keys);
-
-      /* Build "key", "key_len", and "ref" */
-      if (tab_type == JT_NEXT)
-      {
-	key_info= table->key_info+tab->index;
-        key_len= key_info->key_length;
-      }
-      else if (tab->ref.key_parts)
-      {
-	key_info= tab->get_keyinfo_by_key_no(tab->ref.key);
-        key_len= tab->ref.key_length;
-      }
-      
-      /*
-        In STRAIGHT_JOIN queries, there can be join tabs with JT_CONST type
-        that still have quick selects.
-      */
-      if (tab->select && tab->select->quick && tab_type != JT_CONST)
-      {
-        eta->quick_info= tab->select->quick->get_explain(thd->mem_root);
-      }
-
-      if (key_info) /* 'index' or 'ref' access */
-      {
-        eta->key.set(thd->mem_root, key_info->name, key_len);
-
-        if (tab->ref.key_parts && tab_type != JT_FT)
-	{
-          store_key **ref=tab->ref.key_copy;
-          for (uint kp= 0; kp < tab->ref.key_parts; kp++)
-	  {
-	    if (tmp4.length())
-	      tmp4.append(',');
-
-            if ((key_part_map(1) << kp) & tab->ref.const_ref_part_map)
-              tmp4.append("const");
-            else
-            {
-              tmp4.append((*ref)->name(), strlen((*ref)->name()), cs);
-              ref++;
-            }
-          }
-        }
-      }
-  
-      if (tab_type == JT_HASH_NEXT) /* full index scan + hash join */
-      {
-        eta->hash_next_key.set(thd->mem_root, 
-                               table->key_info[tab->index].name, 
-                               table->key_info[tab->index].key_length);
-      }
-
-      if (key_info)
-      {
-        if (key_info && tab_type != JT_NEXT)
-        {
-          eta->ref.copy(tmp4);
-          eta->ref_set= true;
-        }
-        else
-          eta->ref_set= false;
-      }
-      else
-      {
-        if (table_list && /* SJM bushes don't have table_list */
-            table_list->schema_table &&
-            table_list->schema_table->i_s_requested_object & OPTIMIZE_I_S_TABLE)
-        {
-          const char *tmp_buff;
-          int f_idx;
-          StringBuffer<64> key_name_buf;
-          if (table_list->has_db_lookup_value)
-          {
-            /* The "key" has the name of the column referring to the database */
-            f_idx= table_list->schema_table->idx_field1;
-            tmp_buff= table_list->schema_table->fields_info[f_idx].field_name;
-            key_name_buf.append(tmp_buff, strlen(tmp_buff), cs);
-          }          
-          if (table_list->has_table_lookup_value)
-          {
-            if (table_list->has_db_lookup_value)
-              key_name_buf.append(',');
-
-            f_idx= table_list->schema_table->idx_field2;
-            tmp_buff= table_list->schema_table->fields_info[f_idx].field_name;
-            key_name_buf.append(tmp_buff, strlen(tmp_buff), cs);
-          }
-
-          if (key_name_buf.length())
-            eta->key.set(thd->mem_root, key_name_buf.c_ptr_safe(), -1);
-        }
-	eta->ref_set= false;
-      }
-      
-      /* "rows" */
-      if (table_list /* SJM bushes don't have table_list */ &&
-          table_list->schema_table)
-      {
-        /* I_S tables have rows=extra=NULL */
-        eta->rows_set= false;
-        eta->filtered_set= false;
-      }
-      else
-      {
-        double examined_rows= tab->get_examined_rows();
-
-        eta->rows_set= true;
-        eta->rows= (ha_rows) examined_rows;
-
-        /* "filtered"  */
-        float f= 0.0; 
-        if (examined_rows)
-        {
-          double pushdown_cond_selectivity= tab->cond_selectivity;	      
-          if (pushdown_cond_selectivity == 1.0)
-            f= (float) (100.0 * tab->records_read / examined_rows);
-          else
-            f= (float) (100.0 * pushdown_cond_selectivity);
-        }
-        set_if_smaller(f, 100.0);
-        eta->filtered_set= true;
-        eta->filtered= f;
-      }
-
-      /* Build "Extra" field and save it */
-      key_read=table->key_read;
-      if ((tab_type == JT_NEXT || tab_type == JT_CONST) &&
-          table->covering_keys.is_set(tab->index))
-	key_read=1;
-      if (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT &&
-          !((QUICK_ROR_INTERSECT_SELECT*)quick)->need_to_fetch_row)
-        key_read=1;
-        
-      if (tab->info)
-      {
-        eta->push_extra(tab->info);
-      }
-      else if (tab->packed_info & TAB_INFO_HAVE_VALUE)
-      {
-        if (tab->packed_info & TAB_INFO_USING_INDEX)
-          eta->push_extra(ET_USING_INDEX);
-        if (tab->packed_info & TAB_INFO_USING_WHERE)
-          eta->push_extra(ET_USING_WHERE);
-        if (tab->packed_info & TAB_INFO_FULL_SCAN_ON_NULL)
-          eta->push_extra(ET_FULL_SCAN_ON_NULL_KEY);
-      }
-      else
-      {
-        uint keyno= MAX_KEY;
-        if (tab->ref.key_parts)
-          keyno= tab->ref.key;
-        else if (tab->select && quick)
-          keyno = quick->index;
-
-        if (keyno != MAX_KEY && keyno == table->file->pushed_idx_cond_keyno &&
-            table->file->pushed_idx_cond)
-          eta->push_extra(ET_USING_INDEX_CONDITION);
-        else if (tab->cache_idx_cond)
-          eta->push_extra(ET_USING_INDEX_CONDITION_BKA);
-
-        if (quick_type == QUICK_SELECT_I::QS_TYPE_ROR_UNION || 
-            quick_type == QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT ||
-            quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_INTERSECT ||
-            quick_type == QUICK_SELECT_I::QS_TYPE_INDEX_MERGE)
-        {
-          eta->push_extra(ET_USING);
-        }
-	if (tab->select)
-	{
-	  if (tab->use_quick == 2)
-	  {
-            eta->push_extra(ET_RANGE_CHECKED_FOR_EACH_RECORD);
-            eta->range_checked_map= tab->keys;
-	  }
-	  else if (tab->select->cond ||
-                   (tab->cache_select && tab->cache_select->cond))
-          {
-            const COND *pushed_cond= tab->table->file->pushed_cond;
-
-            if (((thd->variables.optimizer_switch &
-                 OPTIMIZER_SWITCH_ENGINE_CONDITION_PUSHDOWN) ||
-                 (tab->table->file->ha_table_flags() &
-                  HA_MUST_USE_TABLE_CONDITION_PUSHDOWN)) &&
-                pushed_cond)
-            {
-              eta->push_extra(ET_USING_WHERE_WITH_PUSHED_CONDITION);
-              /*
-              psergey-todo: what to do? This was useful with NDB only.
-
-              if (explain_flags & DESCRIBE_EXTENDED)
-              {
-                extra.append(STRING_WITH_LEN(": "));
-                ((COND *)pushed_cond)->print(&extra, QT_ORDINARY);
-              }
-              */
-            }
-            else
-              eta->push_extra(ET_USING_WHERE);
-          }
-	}
-        if (table_list /* SJM bushes don't have table_list */ &&
-            table_list->schema_table &&
-            table_list->schema_table->i_s_requested_object & OPTIMIZE_I_S_TABLE)
-        {
-          if (!table_list->table_open_method)
-            eta->push_extra(ET_SKIP_OPEN_TABLE);
-          else if (table_list->table_open_method == OPEN_FRM_ONLY)
-            eta->push_extra(ET_OPEN_FRM_ONLY);
-          else
-            eta->push_extra(ET_OPEN_FULL_TABLE);
-          /* psergey-note: the following has a bug.*/
-          if (table_list->has_db_lookup_value &&
-              table_list->has_table_lookup_value)
-            eta->push_extra(ET_SCANNED_0_DATABASES);
-          else if (table_list->has_db_lookup_value ||
-                   table_list->has_table_lookup_value)
-            eta->push_extra(ET_SCANNED_1_DATABASE);
-          else
-            eta->push_extra(ET_SCANNED_ALL_DATABASES);
-        }
-	if (key_read)
-        {
-          if (quick_type == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
-          {
-            QUICK_GROUP_MIN_MAX_SELECT *qgs= 
-              (QUICK_GROUP_MIN_MAX_SELECT *) tab->select->quick;
-            eta->push_extra(ET_USING_INDEX_FOR_GROUP_BY);
-            eta->loose_scan_is_scanning= qgs->loose_scan_is_scanning();
-          }
-          else
-            eta->push_extra(ET_USING_INDEX);
-        }
-	if (table->reginfo.not_exists_optimize)
-          eta->push_extra(ET_NOT_EXISTS);
-
-        if (quick_type == QUICK_SELECT_I::QS_TYPE_RANGE)
-        {
-          explain_append_mrr_info((QUICK_RANGE_SELECT*)(tab->select->quick),
-                                  &eta->mrr_type);
-          if (eta->mrr_type.length() > 0)
-            eta->push_extra(ET_USING_MRR);
-        }
-
-	if (need_tmp_table)
-	{
-	  need_tmp_table=0;
-          xpl_sel->using_temporary= true;
-	}
-	if (need_order)
-	{
-	  need_order=0;
-          xpl_sel->using_filesort= true;
-	}
-	if (distinct & test_all_bits(used_tables,
-                                     join->select_list_used_tables))
-          eta->push_extra(ET_DISTINCT);
-        if (tab->loosescan_match_tab)
-        {
-          eta->push_extra(ET_LOOSESCAN);
-        }
-
-        if (tab->first_weedout_table)
-          eta->push_extra(ET_START_TEMPORARY);
-        if (tab->check_weed_out_table)
-          eta->push_extra(ET_END_TEMPORARY);
-        else if (tab->do_firstmatch)
-        {
-          if (tab->do_firstmatch == /*join->join_tab*/ first_top_tab - 1)
-            eta->push_extra(ET_FIRST_MATCH);
-          else
-          {
-            eta->push_extra(ET_FIRST_MATCH);
-            TABLE *prev_table=tab->do_firstmatch->table;
-            if (prev_table->derived_select_number)
-            {
-              char namebuf[NAME_LEN];
-              /* Derived table name generation */
-              int len= my_snprintf(namebuf, sizeof(namebuf)-1,
-                                   "<derived%u>",
-                                   prev_table->derived_select_number);
-              eta->firstmatch_table_name.append(namebuf, len);
-            }
-            else
-              eta->firstmatch_table_name.append(prev_table->pos_in_table_list->alias);
-          }
-        }
-
-        for (uint part= 0; part < tab->ref.key_parts; part++)
-        {
-          if (tab->ref.cond_guards[part])
-          {
-            eta->push_extra(ET_FULL_SCAN_ON_NULL_KEY);
-            break;
-          }
-        }
-
-        if (tab->cache)
-	{
-          eta->push_extra(ET_USING_JOIN_BUFFER);
-          tab->cache->save_explain_data(&eta->bka_type);
-        }
       }
 
       if (saved_join_tab)

sql/sql_select.h

@@ -537,6 +537,11 @@ typedef struct st_join_table {
   }
 
   void remove_redundant_bnl_scan_conds();
+
+  void save_explain_data(Explain_table_access *eta, table_map prefix_tables, 
+                         bool distinct, struct st_join_table *first_top_tab);
+
+  void update_explain_data(uint idx);
 } JOIN_TAB;
 
 

sql/sql_show.cc

@@ -121,12 +121,6 @@ append_algorithm(TABLE_LIST *table, String *buff);
 
 static COND * make_cond_for_info_schema(COND *cond, TABLE_LIST *table);
 
-typedef struct st_lookup_field_values
-{
-  LEX_STRING db_value, table_value;
-  bool wild_db_value, wild_table_value;
-} LOOKUP_FIELD_VALUES;
-
 bool get_lookup_field_values(THD *, COND *, TABLE_LIST *, LOOKUP_FIELD_VALUES *);
 
 /***************************************************************************
@@ -4628,6 +4622,10 @@ public:
                   from frm files and storage engine are filled by the function
                   get_all_tables().
 
+  @note           This function assumes optimize_for_get_all_tables() has been
+                  run for the table and produced a "read plan" in 
+                  tables->is_table_read_plan.
+
   @param[in]      thd                      thread handler
   @param[in]      tables                   I_S table
   @param[in]      cond                     'WHERE' condition
@@ -4644,16 +4642,16 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
   TABLE_LIST table_acl_check;
   SELECT_LEX *lsel= tables->schema_select_lex;
   ST_SCHEMA_TABLE *schema_table= tables->schema_table;
-  LOOKUP_FIELD_VALUES lookup_field_vals;
+  IS_table_read_plan *plan= tables->is_table_read_plan;
   enum enum_schema_tables schema_table_idx;
   Dynamic_array<LEX_STRING*> db_names;
-  COND *partial_cond= 0;
+  Item *partial_cond= plan->partial_cond;
   int error= 1;
   Open_tables_backup open_tables_state_backup;
 #ifndef NO_EMBEDDED_ACCESS_CHECKS
   Security_context *sctx= thd->security_ctx;
 #endif
-  uint table_open_method;
+  uint table_open_method= tables->table_open_method;
   bool can_deadlock;
   DBUG_ENTER("get_all_tables");
 
@@ -4677,9 +4675,6 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
   thd->reset_n_backup_open_tables_state(&open_tables_state_backup);
 
   schema_table_idx= get_schema_table_idx(schema_table);
-  tables->table_open_method= table_open_method=
-    get_table_open_method(tables, schema_table, schema_table_idx);
-  DBUG_PRINT("open_method", ("%d", tables->table_open_method));
   /* 
     this branch processes SHOW FIELDS, SHOW INDEXES commands.
     see sql_parse.cc, prepare_schema_table() function where
@@ -4703,44 +4698,12 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
     goto err;
   }
 
-  if (get_lookup_field_values(thd, cond, tables, &lookup_field_vals))
+  if (plan->no_rows)
   {
     error= 0;
     goto err;
   }
 
-  DBUG_PRINT("info",("db_name='%s', table_name='%s'",
-                     lookup_field_vals.db_value.str,
-                     lookup_field_vals.table_value.str));
-
-  if (!lookup_field_vals.wild_db_value && !lookup_field_vals.wild_table_value)
-  {
-    /*
-      if lookup value is empty string then
-      it's impossible table name or db name
-    */
-    if ((lookup_field_vals.db_value.str &&
-         !lookup_field_vals.db_value.str[0]) ||
-        (lookup_field_vals.table_value.str &&
-         !lookup_field_vals.table_value.str[0]))
-    {
-      error= 0;
-      goto err;
-    }
-  }
-
-  if (lookup_field_vals.db_value.length &&
-      !lookup_field_vals.wild_db_value)
-    tables->has_db_lookup_value= TRUE;
-  if (lookup_field_vals.table_value.length &&
-      !lookup_field_vals.wild_table_value)
-    tables->has_table_lookup_value= TRUE;
-
-  if (tables->has_db_lookup_value && tables->has_table_lookup_value)
-    partial_cond= 0;
-  else
-    partial_cond= make_cond_for_info_schema(cond, tables);
-
   if (lex->describe)
   {
     /* EXPLAIN SELECT */
@@ -4750,7 +4713,7 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
 
   bzero((char*) &table_acl_check, sizeof(table_acl_check));
 
-  if (make_db_list(thd, &db_names, &lookup_field_vals))
+  if (make_db_list(thd, &db_names, &plan->lookup_field_vals))
     goto err;
   for (size_t i=0; i < db_names.elements(); i++)
   {
@@ -4765,7 +4728,7 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
     {
       Dynamic_array<LEX_STRING*> table_names;
       int res= make_table_name_list(thd, &table_names, lex,
-                                    &lookup_field_vals, db_name);
+                                    &plan->lookup_field_vals, db_name);
       if (res == 2)   /* Not fatal error, continue */
         continue;
       if (res)
@@ -4802,8 +4765,8 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
             already created by make_table_name_list() function).
           */
           if (!table_open_method && schema_table_idx == SCH_TABLES &&
-              (!lookup_field_vals.table_value.length ||
+              (!plan->lookup_field_vals.table_value.length ||
-               lookup_field_vals.wild_table_value))
+               plan->lookup_field_vals.wild_table_value))
           {
             table->field[0]->store(STRING_WITH_LEN("def"), system_charset_info);
             if (schema_table_store_record(thd, table))
@@ -7979,6 +7942,137 @@ int make_schema_select(THD *thd, SELECT_LEX *sel,
 }
 
 
+/*
+  Optimize reading from an I_S table.
+
+  @detail
+    This function prepares a plan for populating an I_S table with 
+    get_all_tables().
+
+    The plan is in IS_table_read_plan structure, it is saved in
+    tables->is_table_read_plan.
+
+  @return
+    false - Ok
+    true  - Out Of Memory
+    
+*/
+
+static bool optimize_for_get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
+{
+  SELECT_LEX *lsel= tables->schema_select_lex;
+  ST_SCHEMA_TABLE *schema_table= tables->schema_table;
+  enum enum_schema_tables schema_table_idx;
+  IS_table_read_plan *plan;
+  DBUG_ENTER("get_all_tables");
+
+  if (!(plan= new IS_table_read_plan()))
+    DBUG_RETURN(1);
+
+  tables->is_table_read_plan= plan;
+
+  schema_table_idx= get_schema_table_idx(schema_table);
+  tables->table_open_method= get_table_open_method(tables, schema_table, 
+                                                   schema_table_idx);
+  DBUG_PRINT("open_method", ("%d", tables->table_open_method));
+
+  /* 
+    this branch processes SHOW FIELDS, SHOW INDEXES commands.
+    see sql_parse.cc, prepare_schema_table() function where
+    this values are initialized
+  */
+  if (lsel && lsel->table_list.first)
+  {
+    /* These do not need to have a query plan */
+    goto end;
+  }
+
+  if (get_lookup_field_values(thd, cond, tables, &plan->lookup_field_vals))
+  {
+    plan->no_rows= true;
+    goto end;
+  }
+
+  DBUG_PRINT("info",("db_name='%s', table_name='%s'",
+                     plan->lookup_field_vals.db_value.str,
+                     plan->lookup_field_vals.table_value.str));
+
+  if (!plan->lookup_field_vals.wild_db_value && 
+      !plan->lookup_field_vals.wild_table_value)
+  {
+    /*
+      if lookup value is empty string then
+      it's impossible table name or db name
+    */
+    if ((plan->lookup_field_vals.db_value.str &&
+         !plan->lookup_field_vals.db_value.str[0]) ||
+        (plan->lookup_field_vals.table_value.str &&
+         !plan->lookup_field_vals.table_value.str[0]))
+    {
+      plan->no_rows= true;
+      goto end;
+    }
+  }
+
+  if (plan->has_db_lookup_value() && plan->has_table_lookup_value())
+    plan->partial_cond= 0;
+  else
+    plan->partial_cond= make_cond_for_info_schema(cond, tables);
+  
+end:
+  DBUG_RETURN(0);
+}
+
+
+/*
+  This is the optimizer part of get_schema_tables_result().
+*/
+
+bool optimize_schema_tables_reads(JOIN *join)
+{
+  THD *thd= join->thd;
+  bool result= 0;
+  DBUG_ENTER("optimize_schema_tables_reads");
+
+  for (JOIN_TAB *tab= first_linear_tab(join, WITH_CONST_TABLES); 
+       tab; 
+       tab= next_linear_tab(join, tab, WITH_BUSH_ROOTS))
+  {
+    if (!tab->table || !tab->table->pos_in_table_list)
+      continue;
+
+    TABLE_LIST *table_list= tab->table->pos_in_table_list;
+    if (table_list->schema_table && thd->fill_information_schema_tables())
+    {
+      /* A value of 0 indicates a dummy implementation */
+      if (table_list->schema_table->fill_table == 0)
+        continue;
+
+      /* skip I_S optimizations specific to get_all_tables */
+      if (table_list->schema_table->fill_table != get_all_tables)
+        continue;
+
+      Item *cond= tab->select_cond;
+      if (tab->cache_select && tab->cache_select->cond)
+      {
+        /*
+          If join buffering is used, we should use the condition that is
+          attached to the join cache. Cache condition has a part of WHERE that
+          can be checked when we're populating this table.
+          join_tab->select_cond is of no interest, because it only has
+          conditions that depend on both this table and previous tables in the
+          join order.
+        */
+        cond= tab->cache_select->cond;
+      }
+
+      optimize_for_get_all_tables(thd, table_list, cond);
+    }
+  }
+  DBUG_RETURN(result);
+}
+
+
 /*
   Fill temporary schema tables before SELECT
 
@@ -7987,6 +8081,10 @@ int make_schema_select(THD *thd, SELECT_LEX *sel,
     join  join which use schema tables
     executed_place place where I_S table processed
 
+  SEE ALSO
+    The optimization part is done by get_schema_tables_result(). This function
+    is run on query execution.
+
   RETURN
     FALSE success
     TRUE  error
@@ -8007,7 +8105,7 @@ bool get_schema_tables_result(JOIN *join,
 
   for (JOIN_TAB *tab= first_linear_tab(join, WITH_CONST_TABLES); 
        tab; 
-       tab= next_linear_tab(join, tab, WITHOUT_BUSH_ROOTS))
+       tab= next_linear_tab(join, tab, WITH_BUSH_ROOTS))
   {
     if (!tab->table || !tab->table->pos_in_table_list)
       break;

sql/sql_show.h

@@ -150,6 +150,41 @@ public:
   void call_in_target_thread();
 };
 
+typedef struct st_lookup_field_values
+{
+  LEX_STRING db_value, table_value;
+  bool wild_db_value, wild_table_value;
+} LOOKUP_FIELD_VALUES;
+
+
+/*
+  INFORMATION_SCHEMA: Execution plan for get_all_tables() call
+*/
+
+class IS_table_read_plan : public Sql_alloc
+{
+public:
+  IS_table_read_plan() : no_rows(false) {}
+
+  bool no_rows;
+
+  LOOKUP_FIELD_VALUES lookup_field_vals;
+  Item *partial_cond;
+
+  bool has_db_lookup_value()
+  {
+    return (lookup_field_vals.db_value.length &&
+           !lookup_field_vals.wild_db_value);
+  }
+  bool has_table_lookup_value()
+  {
+    return (lookup_field_vals.table_value.length &&
+            !lookup_field_vals.wild_table_value);
+  }
+};
+
+bool optimize_schema_tables_reads(JOIN *join);
+
 /* Handle the ignored database directories list for SHOW/I_S. */
 bool ignore_db_dirs_init();
 void ignore_db_dirs_free();

sql/table.h

@@ -1499,6 +1499,7 @@ typedef struct st_schema_table
   uint i_s_requested_object;  /* the object we need to open(TABLE | VIEW) */
 } ST_SCHEMA_TABLE;
 
+class IS_table_read_plan;
 
 /*
   Types of derived tables. The ending part is a bitmap of phases that are
@@ -2044,12 +2045,23 @@ struct TABLE_LIST
   /* TRUE <=> this table is a const one and was optimized away. */
   bool optimized_away;
 
+  /* I_S: Flags to open_table (e.g. OPEN_TABLE_ONLY or OPEN_VIEW_ONLY) */
   uint i_s_requested_object;
-  bool has_db_lookup_value;
+
-  bool has_table_lookup_value;
+  /*
+    I_S: how to read the tables (SKIP_OPEN_TABLE/OPEN_FRM_ONLY/OPEN_FULL_TABLE)
+  */
   uint table_open_method;
+  /*
+    I_S: where the schema table was filled
+    (this is a hack. The code should be able to figure out whether reading
+    from I_S should be done by create_sort_index() or by JOIN::exec.)
+  */
   enum enum_schema_table_state schema_table_state;
 
+  /* Something like a "query plan" for reading INFORMATION_SCHEMA table */
+  IS_table_read_plan *is_table_read_plan;
+
   MDL_request mdl_request;
 
 #ifdef WITH_PARTITION_STORAGE_ENGINE