MDEV-7811: EXPLAIN/ANALYZE FORMAT=JSON should show subquery cache

Fixes over the original patch:
- Fix variable/class/other names
- Fix the JSON output to be in line with the output of other JSON
  constructs we produce

mysql-test/r/subselect_cache.result

@@ -59,17 +59,13 @@ ANALYZE
     },
     "subqueries": [
       {
+        "expression_cache": {
+          "r_loops": 10,
+          "r_hit_ratio": 60,
           "query_block": {
             "select_id": 2,
             "r_loops": 4,
             "r_total_time_ms": "REPLACED",
-          "expression_cache": {
-            "state": "ENABLED",
-            "r_hit": 6,
-            "r_miss": 4,
-            "r_loops": 10,
-            "r_hit_ratio": 60
-          },
             "table": {
               "table_name": "t2",
               "access_type": "ALL",
@@ -83,6 +79,7 @@ ANALYZE
             }
           }
         }
+      }
     ]
   }
 }
@@ -106,19 +103,15 @@ ANALYZE
     },
     "subqueries": [
       {
+        "expression_cache": {
+          "r_loops": 10,
+          "r_hit_ratio": 60,
           "query_block": {
             "union_result": {
               "table_name": "<union3,4>",
               "access_type": "ALL",
               "r_loops": 4,
               "r_rows": 1,
-            "expression_cache": {
-              "state": "ENABLED",
-              "r_hit": 6,
-              "r_miss": 4,
-              "r_loops": 10,
-              "r_hit_ratio": 60
-            },
               "query_specifications": [
                 {
                   "query_block": {
@@ -149,19 +142,16 @@ ANALYZE
               ]
             }
           }
+        }
       },
       {
+        "expression_cache": {
+          "r_loops": 10,
+          "r_hit_ratio": 60,
           "query_block": {
             "select_id": 2,
             "r_loops": 4,
             "r_total_time_ms": "REPLACED",
-          "expression_cache": {
-            "state": "ENABLED",
-            "r_hit": 6,
-            "r_miss": 4,
-            "r_loops": 10,
-            "r_hit_ratio": 60
-          },
             "table": {
               "table_name": "t2",
               "access_type": "ALL",
@@ -175,6 +165,7 @@ ANALYZE
             }
           }
         }
+      }
     ]
   }
 }
@@ -192,11 +183,10 @@ EXPLAIN
     },
     "subqueries": [
       {
+        "expression_cache": {
+          "state": "uninitialized",
           "query_block": {
             "select_id": 2,
-          "expression_cache": {
-            "state": "UNINITIALYZED"
-          },
             "table": {
               "table_name": "t2",
               "access_type": "ALL",
@@ -206,6 +196,7 @@ EXPLAIN
             }
           }
         }
+      }
     ]
   }
 }
@@ -223,13 +214,12 @@ EXPLAIN
     },
     "subqueries": [
       {
+        "expression_cache": {
+          "state": "uninitialized",
           "query_block": {
             "union_result": {
               "table_name": "<union3,4>",
               "access_type": "ALL",
-            "expression_cache": {
-              "state": "UNINITIALYZED"
-            },
               "query_specifications": [
                 {
                   "query_block": {
@@ -254,13 +244,13 @@ EXPLAIN
               ]
             }
           }
+        }
       },
       {
+        "expression_cache": {
+          "state": "uninitialized",
           "query_block": {
             "select_id": 2,
-          "expression_cache": {
-            "state": "UNINITIALYZED"
-          },
             "table": {
               "table_name": "t2",
               "access_type": "ALL",
@@ -270,6 +260,7 @@ EXPLAIN
             }
           }
         }
+      }
     ]
   }
 }

sql/item.cc

@@ -7554,15 +7554,15 @@ bool Item_cache_wrapper::set_cache(THD *thd)
   DBUG_RETURN(expr_cache == NULL);
 }
 
-Expression_cache_stat* Item_cache_wrapper::set_stat(MEM_ROOT *mem_root)
+Expression_cache_tracker* Item_cache_wrapper::init_tracker(MEM_ROOT *mem_root)
 {
   if (expr_cache)
   {
-    Expression_cache_stat* stat=
-      new(mem_root) Expression_cache_stat(expr_cache);
-    if (stat)
-      ((Expression_cache_tmptable *)expr_cache)->set_stat(stat);
-    return stat;
+    Expression_cache_tracker* tracker=
+      new(mem_root) Expression_cache_tracker(expr_cache);
+    if (tracker)
+      ((Expression_cache_tmptable *)expr_cache)->set_tracker(tracker);
+    return tracker;
   }
   return NULL;
 }

sql/item.h

@@ -3804,7 +3804,7 @@ public:
 
 class Item_cache;
 class Expression_cache;
-class Expression_cache_stat;
+class Expression_cache_tracker;
 
 /**
   The objects of this class can store its values in an expression cache.
@@ -3839,7 +3839,7 @@ public:
   enum Type real_type() const { return orig_item->type(); }
 
   bool set_cache(THD *thd);
-  Expression_cache_stat* set_stat(MEM_ROOT *mem_root);
+  Expression_cache_tracker* init_tracker(MEM_ROOT *mem_root);
 
   bool fix_fields(THD *thd, Item **it);
   void cleanup();

sql/item_subselect.cc

@@ -1202,7 +1202,7 @@ Item* Item_singlerow_subselect::expr_cache_insert_transformer(uchar *thd_arg)
   if (expr_cache_is_needed(thd) &&
       (expr_cache= set_expr_cache(thd)))
   {
-    set_expr_cache_stat(thd);
+    init_expr_cache_tracker(thd);
     DBUG_RETURN(expr_cache);
   }
   DBUG_RETURN(this);
@@ -1501,7 +1501,7 @@ Item* Item_exists_subselect::expr_cache_insert_transformer(uchar *thd_arg)
   if (substype() == EXISTS_SUBS && expr_cache_is_needed(thd) &&
       (expr_cache= set_expr_cache(thd)))
   {
-    set_expr_cache_stat(thd);
+    init_expr_cache_tracker(thd);
     DBUG_RETURN(expr_cache);
   }
   DBUG_RETURN(this);
@@ -6562,7 +6562,13 @@ void subselect_table_scan_engine::cleanup()
 {
 }
 
-void Item_subselect::set_expr_cache_stat(THD *thd)
+
+/*
+  Create an execution tracker for the expression cache we're using for this
+  subselect; add the tracker to the query plan.
+*/
+
+void Item_subselect::init_expr_cache_tracker(THD *thd)
 {
   if(!expr_cache)
     return;
@@ -6573,5 +6579,6 @@ void Item_subselect::set_expr_cache_stat(THD *thd)
   if (!node)
     return;
   DBUG_ASSERT(expr_cache->type() == Item::EXPR_CACHE_ITEM);
-  node->cache_stat= ((Item_cache_wrapper *)expr_cache)->set_stat(qw->mem_root);
+  node->cache_tracker= ((Item_cache_wrapper *)expr_cache)->init_tracker(qw->mem_root);
 }
+

sql/item_subselect.h

@@ -246,7 +246,7 @@ public:
     return TRUE;
   }
 
-  void set_expr_cache_stat(THD *thd);
+  void init_expr_cache_tracker(THD *thd);
 
 
   friend class select_result_interceptor;

sql/sql_explain.cc

@@ -521,6 +521,8 @@ void Explain_union::print_explain_json(Explain_query *query,
   Json_writer_nesting_guard guard(writer);
   char table_name_buffer[SAFE_NAME_LEN];
   
+  bool started_object= print_explain_json_cache(writer, is_analyze);
+
   writer->add_member("query_block").start_object();
   writer->add_member("union_result").start_object();
   // using_temporary_table
@@ -544,7 +546,6 @@ void Explain_union::print_explain_json(Explain_query *query,
       writer->add_null();
   }
 
-  print_explain_json_cache(writer, is_analyze);
   writer->add_member("query_specifications").start_array();
 
   for (int i= 0; i < (int) union_members.elements(); i++)
@@ -562,6 +563,9 @@ void Explain_union::print_explain_json(Explain_query *query,
 
   writer->end_object(); // union_result
   writer->end_object(); // query_block
+
+  if (started_object)
+    writer->end_object();
 }
 
 
@@ -642,27 +646,32 @@ void Explain_node::print_explain_json_for_children(Explain_query *query,
 }
 
 
-void Explain_node::print_explain_json_cache(Json_writer *writer,
+bool Explain_node::print_explain_json_cache(Json_writer *writer,
                                             bool is_analyze)
 {
-    if (cache_stat)
+  if (cache_tracker)
   {
-      cache_stat->flush_stat();
+    cache_tracker->fetch_current_stats();
     writer->add_member("expression_cache").start_object();
+    if (cache_tracker->state != Expression_cache_tracker::OK)
+    {
       writer->add_member("state").
-        add_str(Expression_cache_stat::state_str[cache_stat->state]);
+        add_str(Expression_cache_tracker::state_str[cache_tracker->state]);
+    }
+
     if (is_analyze)
     {
-        writer->add_member("r_hit").add_ll(cache_stat->hit);
-        writer->add_member("r_miss").add_ll(cache_stat->miss);
-        writer->add_member("r_loops").add_ll(cache_stat->hit +
-                                             cache_stat->miss);
-        writer->add_member("r_hit_ratio").add_ll(((double)cache_stat->hit)/
-                                             ((double)(cache_stat->hit +
-                                             cache_stat->miss)) * 100.0);
+      longlong cache_reads= cache_tracker->hit + cache_tracker->miss;
+      writer->add_member("r_loops").add_ll(cache_reads);
+      if (cache_reads != 0) 
+      {
+        double hit_ratio= double(cache_tracker->hit) / cache_reads * 100.0;
+        writer->add_member("r_hit_ratio").add_double(hit_ratio);
       }
-      writer->end_object();
     }
+    return true;
+  }
+  return false;
 }
 
 
@@ -767,6 +776,8 @@ void Explain_select::print_explain_json(Explain_query *query,
 {
   Json_writer_nesting_guard guard(writer);
   
+  bool started_cache= print_explain_json_cache(writer, is_analyze);
+
   if (message)
   {
     writer->add_member("query_block").start_object();
@@ -795,7 +806,6 @@ void Explain_select::print_explain_json(Explain_query *query,
       writer->add_member("const_condition");
       write_item(writer, exec_const_cond);
     }
-    print_explain_json_cache(writer, is_analyze);
      
     Filesort_tracker *first_table_sort= NULL;
     bool first_table_sort_used= false;
@@ -887,6 +897,8 @@ void Explain_select::print_explain_json(Explain_query *query,
     writer->end_object();
   }
 
+  if (started_cache)
+    writer->end_object();
 }
 
 

sql/sql_explain.h

@@ -85,7 +85,7 @@ class Explain_node : public Sql_alloc
 {
 public:
   Explain_node(MEM_ROOT *root) :
-    cache_stat(NULL),
+    cache_tracker(NULL),
     connection_type(EXPLAIN_NODE_OTHER),
     children(root)
   {}
@@ -113,7 +113,7 @@ public:
   /**
     expression cache statistics
   */
-  Expression_cache_stat* cache_stat;
+  Expression_cache_tracker* cache_tracker;
 
   /*
     How this node is connected to its parent.
@@ -140,7 +140,7 @@ public:
                                  uint8 explain_flags, bool is_analyze);
   void print_explain_json_for_children(Explain_query *query,
                                        Json_writer *writer, bool is_analyze);
-  void print_explain_json_cache(Json_writer *writer, bool is_analyze);
+  bool print_explain_json_cache(Json_writer *writer, bool is_analyze);
   virtual ~Explain_node(){}
 };
 

sql/sql_expression_cache.cc

@@ -43,7 +43,7 @@ ulong subquery_cache_miss, subquery_cache_hit;
 Expression_cache_tmptable::Expression_cache_tmptable(THD *thd,
                                                      List<Item> &dependants,
                                                      Item *value)
-  :cache_table(NULL), table_thd(thd), stat(NULL), items(dependants), val(value),
+  :cache_table(NULL), table_thd(thd), tracker(NULL), items(dependants), val(value),
    hit(0), miss(0), inited (0)
 {
   DBUG_ENTER("Expression_cache_tmptable::Expression_cache_tmptable");
@@ -61,9 +61,9 @@ void Expression_cache_tmptable::disable_cache()
     cache_table->file->ha_index_end();
   free_tmp_table(table_thd, cache_table);
   cache_table= NULL;
-  flush_stat();
-  if (stat)
-    stat->cache= NULL;
+  update_tracker();
+  if (tracker)
+    tracker->cache= NULL;
 }
 
 
@@ -167,7 +167,7 @@ void Expression_cache_tmptable::init()
     goto error;
   }
 
-  flush_stat();
+  update_tracker();
   DBUG_VOID_RETURN;
 
 error:
@@ -186,8 +186,8 @@ Expression_cache_tmptable::~Expression_cache_tmptable()
     disable_cache();
   else
   {
-    flush_stat();
-    stat= NULL;
+    update_tracker();
+    tracker= NULL;
   }
 }
 
@@ -334,5 +334,5 @@ void Expression_cache_tmptable::print(String *str, enum_query_type query_type)
 }
 
 
-const char *Expression_cache_stat::state_str[3]=
-{"UNINITIALYZED", "DISABLED", "ENABLED"};
+const char *Expression_cache_tracker::state_str[3]=
+{"uninitialized", "disabled", "enabled"};

sql/sql_expression_cache.h

@@ -65,9 +65,9 @@ public:
   virtual void init()= 0;
 
   /**
-    Save this object's statistics into Expression_cache_stat object
+    Save this object's statistics into Expression_cache_tracker object
   */
-  virtual void flush_stat()= 0;
+  virtual void update_tracker()= 0;
 };
 
 struct st_table_ref;
@@ -75,11 +75,11 @@ struct st_join_table;
 class Item_field;
 
 
-class Expression_cache_stat :public Sql_alloc
+class Expression_cache_tracker :public Sql_alloc
 {
 public:
   enum expr_cache_state {UNINITED, STOPPED, OK};
-  Expression_cache_stat(Expression_cache *c) :
+  Expression_cache_tracker(Expression_cache *c) :
     cache(c), hit(0), miss(0), state(UNINITED)
   {}
 
@@ -91,10 +91,10 @@ public:
   void set(ulong h, ulong m, enum expr_cache_state s)
   {hit= h; miss= m; state= s;}
 
-  void flush_stat()
+  void fetch_current_stats()
   {
     if (cache)
-      cache->flush_stat();
+      cache->update_tracker();
   }
 };
 
@@ -115,18 +115,20 @@ public:
   bool is_inited() { return inited; };
   void init();
 
-  void set_stat(Expression_cache_stat *st)
+  void set_tracker(Expression_cache_tracker *st)
   {
-    stat= st;
-    flush_stat();
+    tracker= st;
+    update_tracker();
   }
-  virtual void flush_stat()
+  virtual void update_tracker()
   {
-    if (stat)
-      stat->set(hit, miss, (inited ? (cache_table ?
-                                      Expression_cache_stat::OK :
-                                      Expression_cache_stat::STOPPED) :
-                            Expression_cache_stat::UNINITED));
+    if (tracker)
+    {
+      tracker->set(hit, miss, (inited ? (cache_table ?
+                                         Expression_cache_tracker::OK :
+                                         Expression_cache_tracker::STOPPED) :
+                               Expression_cache_tracker::UNINITED));
+    }
   }
 
 private:
@@ -139,7 +141,7 @@ private:
   /* Thread handle for the temporary table */
   THD *table_thd;
   /* EXPALIN/ANALYZE statistics */
-  Expression_cache_stat *stat;
+  Expression_cache_tracker *tracker;
   /* TABLE_REF for index lookup */
   struct st_table_ref ref;
   /* Cached result */