MDEV-3798: EXPLAIN UPDATE/DELETE

Update the SHOW EXPLAIN code to work with the 
new architecture (part#1):
Before, SHOW EXPLAIN operated on real query plan structures, 
which meant it had to check when SELECTs are created/deleted.
SELECTs would call apc_target->enable() when they got a query 
plan and disable() when their query plan was deleted.

Now, Explain data structure becomes available at once (and we
call apc_target->enable()) and then it stays until it is deleted
(when that happens, we call apc_target->disable()).

mysql-test/r/show_explain.result

@@ -181,6 +181,8 @@ set debug_dbug='+d,show_explain_probe_join_exec_start';
 set @foo= (select max(a) from t0 where sin(a) >0);
 show explain for $thr2;
 ERROR HY000: Target is not running an EXPLAINable command
+kill query $thr2;
+ERROR 70100: Query execution was interrupted
 set debug_dbug=@old_debug;
 #
 # Attempt SHOW EXPLAIN for an UPDATE
@@ -405,13 +407,8 @@ set debug_dbug='+d,show_explain_probe_join_exec_end';
 SELECT * FROM v1, t2;
 show explain for $thr2;
 ERROR HY000: Target is not running an EXPLAINable command
-a	b
-8	4
-8	5
-8	6
-8	7
-8	8
-8	9
+kill query $thr2;
+ERROR 70100: Query execution was interrupted
 set debug_dbug=@old_debug;
 DROP VIEW v1;
 DROP TABLE t2, t3;

mysql-test/t/show_explain.test

@@ -224,7 +224,9 @@ connection default;
 --source include/wait_condition.inc
 --error ER_TARGET_NOT_EXPLAINABLE
 evalp show explain for $thr2;
+evalp kill query $thr2;
 connection con1;
+--error ER_QUERY_INTERRUPTED
 reap;
 set debug_dbug=@old_debug;
 
@@ -399,7 +401,9 @@ connection default;
 --source include/wait_condition.inc
 --error ER_TARGET_NOT_EXPLAINABLE
 evalp show explain for $thr2;
+evalp kill query $thr2;
 connection con1;
+--error ER_QUERY_INTERRUPTED
 reap;
 set debug_dbug=@old_debug;
 DROP VIEW v1;

sql/sp_head.cc

@@ -3037,7 +3037,7 @@ sp_lex_keeper::reset_lex_and_exec_core(THD *thd, uint *nextp,
     else if (! thd->in_sub_stmt)
       thd->mdl_context.release_statement_locks();
   }
-  
+  //TODO: why is this here if log_slow_query is in sp_instr_stmt_execute? 
   delete_explain_query(m_lex);
 
   if (m_lex->query_tables_own_last)

sql/sql_delete.cc

@@ -66,8 +66,8 @@ void Delete_plan::save_explain_data(Explain_query *query)
     explain->deleting_all_rows= false;
     Update_plan::save_explain_data_intern(query, explain);
   }
-
-  query->upd_del_plan= explain;
+ 
+  query->add_upd_del_plan(explain);
 }
 
 
@@ -75,7 +75,7 @@ void Update_plan::save_explain_data(Explain_query *query)
 {
   Explain_update* explain= new Explain_update;
   save_explain_data_intern(query, explain);
-  query->upd_del_plan= explain;
+  query->add_upd_del_plan(explain);
 }
 
 
@@ -459,7 +459,6 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
     goto exit_without_my_ok;
 
   query_plan.save_explain_data(thd->lex->explain);
-  thd->apc_target.enable();
 
   DBUG_EXECUTE_IF("show_explain_probe_delete_exec_start", 
                   dbug_serve_apcs(thd, 1););
@@ -486,7 +485,6 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
       {
         delete select;
         free_underlaid_joins(thd, &thd->lex->select_lex);
-        thd->apc_target.disable();
         DBUG_RETURN(TRUE);
       }
       thd->examined_row_count+= examined_rows;
@@ -505,7 +503,6 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
   {
     delete select;
     free_underlaid_joins(thd, select_lex);
-    thd->apc_target.disable();
     DBUG_RETURN(TRUE);
   }
   if (query_plan.index == MAX_KEY || (select && select->quick))
@@ -514,7 +511,6 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
     {
       delete select;
       free_underlaid_joins(thd, select_lex);
-      thd->apc_target.disable();
       DBUG_RETURN(TRUE);
     }
   }
@@ -624,7 +620,6 @@ bool mysql_delete(THD *thd, TABLE_LIST *table_list, COND *conds,
   if (options & OPTION_QUICK)
     (void) table->file->extra(HA_EXTRA_NORMAL);
 
-  thd->apc_target.disable();
 cleanup:
   /*
     Invalidate the table in the query cache if something changed. This must

sql/sql_explain.cc

@@ -22,7 +22,8 @@
 #include "sql_select.h"
 
 
-Explain_query::Explain_query() : upd_del_plan(NULL), insert_plan(NULL)
+Explain_query::Explain_query(THD *thd_arg) : 
+  upd_del_plan(NULL), insert_plan(NULL), thd(thd_arg), apc_enabled(false)
 {
   operations= 0;
 }
@@ -30,6 +31,9 @@ Explain_query::Explain_query() : upd_del_plan(NULL), insert_plan(NULL)
 
 Explain_query::~Explain_query()
 {
+  if (apc_enabled)
+    thd->apc_target.disable();
+
   delete upd_del_plan;
   delete insert_plan;
   uint i;
@@ -62,11 +66,12 @@ Explain_select *Explain_query::get_select(uint select_id)
 
 void Explain_query::add_node(Explain_node *node)
 {
+  uint select_id;
   operations++;
   if (node->get_type() == Explain_node::EXPLAIN_UNION)
   {
     Explain_union *u= (Explain_union*)node;
-    uint select_id= u->get_select_id();
+    select_id= u->get_select_id();
     if (unions.elements() <= select_id)
       unions.resize(max(select_id+1, unions.elements()*2), NULL);
 
@@ -85,7 +90,7 @@ void Explain_query::add_node(Explain_node *node)
     }
     else
     {
-      uint select_id= sel->select_id;
+      select_id= sel->select_id;
       Explain_select *old_node;
 
       if (selects.elements() <= select_id)
@@ -100,6 +105,27 @@ void Explain_query::add_node(Explain_node *node)
 }
 
 
+void Explain_query::add_insert_plan(Explain_insert *insert_plan_arg)
+{
+  insert_plan= insert_plan_arg;
+  query_plan_ready();
+}
+
+
+void Explain_query::add_upd_del_plan(Explain_update *upd_del_plan_arg)
+{
+  upd_del_plan= upd_del_plan_arg;
+  query_plan_ready();
+}
+
+
+void Explain_query::query_plan_ready()
+{
+  if (!apc_enabled)
+    thd->apc_target.enable();
+  apc_enabled= true;
+}
+
 /*
   Send EXPLAIN output to the client.
 */
@@ -915,7 +941,7 @@ void delete_explain_query(LEX *lex)
 void create_explain_query(LEX *lex, MEM_ROOT *mem_root)
 {
   DBUG_ASSERT(!lex->explain);
-  lex->explain= new Explain_query;
+  lex->explain= new Explain_query(lex->thd);
   DBUG_ASSERT(mem_root == current_thd->mem_root);
   lex->explain->mem_root= mem_root;
 }

sql/sql_explain.h

@@ -221,10 +221,13 @@ class Explain_insert;
 class Explain_query : public Sql_alloc
 {
 public:
-  Explain_query();
+  Explain_query(THD *thd);
   ~Explain_query();
+
   /* Add a new node */
   void add_node(Explain_node *node);
+  void add_insert_plan(Explain_insert *insert_plan_arg);
+  void add_upd_del_plan(Explain_update *upd_del_plan_arg);
 
   /* This will return a select, or a union */
   Explain_node *get_node(uint select_id);
@@ -233,13 +236,7 @@ public:
   Explain_select *get_select(uint select_id);
   
   Explain_union *get_union(uint select_id);
-  
-  /* Explain_delete inherits from Explain_update */
-  Explain_update *upd_del_plan;
-
-  /* Query "plan" for INSERTs */
-  Explain_insert *insert_plan;
-
+ 
   /* Produce a tabular EXPLAIN output */
   int print_explain(select_result_sink *output, uint8 explain_flags);
   
@@ -251,11 +248,22 @@ public:
 
   /* If true, at least part of EXPLAIN can be printed */
   bool have_query_plan() { return insert_plan || upd_del_plan|| get_node(1) != NULL; }
+
+  void query_plan_ready();
+
   MEM_ROOT *mem_root;
 private:
+  /* Explain_delete inherits from Explain_update */
+  Explain_update *upd_del_plan;
+
+  /* Query "plan" for INSERTs */
+  Explain_insert *insert_plan;
+
   Dynamic_array<Explain_union*> unions;
   Dynamic_array<Explain_select*> selects;
   
+  THD *thd; // for APC start/stop
+  bool apc_enabled;
   /* 
     Debugging aid: count how many times add_node() was called. Ideally, it
     should be one, we currently allow O(1) query plan saves for each

sql/sql_insert.cc

@@ -461,7 +461,8 @@ void upgrade_lock_type(THD *thd, thr_lock_type *lock_type,
     if (specialflag & (SPECIAL_NO_NEW_FUNC | SPECIAL_SAFE_MODE) ||
         thd->variables.max_insert_delayed_threads == 0 ||
         thd->locked_tables_mode > LTM_LOCK_TABLES ||
-        thd->lex->uses_stored_routines())
+        thd->lex->uses_stored_routines() /*||
+        thd->lex->describe*/)
     {
       *lock_type= TL_WRITE;
       return;
@@ -649,7 +650,7 @@ static void save_insert_query_plan(THD* thd, TABLE_LIST *table_list)
   Explain_insert* explain= new Explain_insert;
   explain->table_name.append(table_list->table->alias);
 
-  thd->lex->explain->insert_plan= explain;
+  thd->lex->explain->add_insert_plan(explain);
   
   /* See Update_plan::updating_a_view for details */
   bool skip= test(table_list->view);

sql/sql_lex.cc

@@ -4276,11 +4276,15 @@ int st_select_lex_unit::save_union_explain(Explain_query *output)
   for (SELECT_LEX *sl= first; sl; sl= sl->next_select())
     eu->add_select(sl->select_number);
 
+  eu->fake_select_type= "UNION RESULT";
+  eu->using_filesort= test(global_parameters->order_list.first);
+
   // Save the UNION node
   output->add_node(eu);
 
-  eu->fake_select_type= "UNION RESULT";
-  eu->using_filesort= test(global_parameters->order_list.first);
+  if (eu->get_select_id() == 1)
+    output->query_plan_ready();
+
   return 0;
 }
 

sql/sql_lex.h

@@ -1031,6 +1031,10 @@ public:
 
   void clear_index_hints(void) { index_hints= NULL; }
   bool is_part_of_union() { return master_unit()->is_union(); }
+  bool is_top_level_node() 
+  { 
+    return (select_number == 1) && !is_part_of_union();
+  }
   bool optimize_unflattened_subqueries(bool const_only);
   /* Set the EXPLAIN type for this subquery. */
   void set_explain_type(bool on_the_fly);

sql/sql_select.cc

@@ -2298,8 +2298,6 @@ JOIN::save_join_tab()
 void join_save_qpf(JOIN *join)
 {
   THD *thd= join->thd;
-//TODO: why not call st_select_lex::save_qpf here?
-
   if (join->select_lex->select_number != UINT_MAX && 
       join->select_lex->select_number != INT_MAX /* this is not a UNION's "fake select */ && 
       join->have_query_plan != JOIN::QEP_NOT_PRESENT_YET && 
@@ -2315,7 +2313,7 @@ void join_save_qpf(JOIN *join)
       /* It's a degenerate join */
       message= join->zero_result_cause ? join->zero_result_cause : "No tables used";
     }
-
+    
     join->save_explain_data(thd->lex->explain,
                             join->need_tmp,
                             !join->skip_sort_order && !join->no_order &&
@@ -2328,7 +2326,6 @@ void join_save_qpf(JOIN *join)
 
 void JOIN::exec()
 {
-  thd->apc_target.enable();
   DBUG_EXECUTE_IF("show_explain_probe_join_exec_start", 
                   if (dbug_user_var_equals_int(thd, 
                                                "show_explain_probe_select_id", 
@@ -2368,7 +2365,6 @@ void JOIN::exec()
                                                select_lex->select_number))
                         dbug_serve_apcs(thd, 1);
                  );
-  thd->apc_target.disable();
 }
 
 
@@ -22997,6 +22993,10 @@ int JOIN::save_explain_data(Explain_query *output, bool need_tmp_table,
     }
   }
 
+  if (!error && select_lex->is_top_level_node())
+    output->query_plan_ready();
+    
+
   DBUG_RETURN(error);
 }
 

sql/sql_update.cc

@@ -279,7 +279,6 @@ int mysql_update(THD *thd,
   Update_plan query_plan(thd->mem_root);
   query_plan.index= MAX_KEY;
   query_plan.using_filesort= FALSE;
-  bool apc_target_enabled= false; // means was enabled *by code this function*
   DBUG_ENTER("mysql_update");
 
   if (open_tables(thd, &table_list, &table_count, 0))
@@ -518,8 +517,6 @@ int mysql_update(THD *thd,
     goto exit_without_my_ok;
   query_plan.save_explain_data(thd->lex->explain);
 
-  thd->apc_target.enable();
-  apc_target_enabled= true;
   DBUG_EXECUTE_IF("show_explain_probe_update_exec_start", 
                   dbug_serve_apcs(thd, 1););
   
@@ -960,8 +957,6 @@ int mysql_update(THD *thd,
   if (!transactional_table && updated > 0)
     thd->transaction.stmt.modified_non_trans_table= TRUE;
 
-  thd->apc_target.disable();
-  apc_target_enabled= false;
   end_read_record(&info);
   delete select;
   thd_proc_info(thd, "end");
@@ -1035,8 +1030,6 @@ int mysql_update(THD *thd,
   DBUG_RETURN((error >= 0 || thd->is_error()) ? 1 : 0);
 
 err:
-  if (apc_target_enabled)
-    thd->apc_target.disable();
 
   delete select;
   free_underlaid_joins(thd, select_lex);
@@ -1045,7 +1038,6 @@ err:
   DBUG_RETURN(1);
 
 exit_without_my_ok:
-  DBUG_ASSERT(!apc_target_enabled);
   query_plan.save_explain_data(thd->lex->explain);
 
   int err2= thd->lex->explain->send_explain(thd);