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

@@ -129,6 +129,12 @@ public:
     join_tabs[n_join_tabs++]= tab;
     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;

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.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 ||
-               lookup_field_vals.wild_table_value))
+              (!plan->lookup_field_vals.table_value.length ||
+               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