EXPLAIN FORMAT=JSON: Support "range checked for each record"

mysql-test/r/explain_json.result

@@ -691,5 +691,31 @@ EXPLAIN
     }
   }
 }
+# 'Range checked for each record'
+set optimizer_switch=@tmp;
+explain format=json
+select * from t1 tbl1, t1 tbl2 where tbl2.a < tbl1.b;
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "tbl1",
+      "access_type": "ALL",
+      "rows": 100,
+      "filtered": 100
+    },
+    "range-checked-for-each-record": {
+      "keys": ["a"],
+      "table": {
+        "table_name": "tbl2",
+        "access_type": "ALL",
+        "possible_keys": ["a"],
+        "rows": 100,
+        "filtered": 100
+      }
+    }
+  }
+}
 drop table t1;
 drop table t0;

mysql-test/t/explain_json.test

@@ -145,6 +145,11 @@ set optimizer_switch='mrr=on,mrr_sort_keys=on';
 
 explain format=json select * from t1 where a < 3;
 
+--echo # 'Range checked for each record'
+set optimizer_switch=@tmp;
+explain format=json
+select * from t1 tbl1, t1 tbl2 where tbl2.a < tbl1.b;
+
 drop table t1;
 drop table t0;
 

sql/sql_explain.cc

@@ -1132,6 +1132,8 @@ void Explain_table_access::tag_to_json(Json_writer *writer, enum explain_extra_t
     case ET_USING:
       // index merge: case ET_USING 
       break;
+    case ET_RANGE_CHECKED_FOR_EACH_RECORD:
+      /* Handled as range_checked_fer */
     case ET_USING_JOIN_BUFFER:
       /* Do nothing. Join buffer is handled differently */
     case ET_START_TEMPORARY:
@@ -1153,6 +1155,22 @@ void Explain_table_access::tag_to_json(Json_writer *writer, enum explain_extra_t
 }
 
 
+static
+void add_json_keyset(Json_writer *writer, const char *elem_name,
+                     String_list *keyset)
+{
+  if (!keyset->is_empty())
+  {
+    List_iterator_fast<char> it(*keyset);
+    const char *name;
+    writer->add_member(elem_name).start_array();
+    while ((name= it++))
+      writer->add_str(name);
+    writer->end_array();
+  }
+}
+
+
 void Explain_table_access::print_explain_json(Explain_query *query,
                                               Json_writer *writer,
                                               bool is_analyze)
@@ -1164,20 +1182,19 @@ void Explain_table_access::print_explain_json(Explain_query *query,
     writer->add_member("block-nl-join").start_object();
   }
 
+  if (range_checked_fer)
+  {
+    writer->add_member("range-checked-for-each-record").start_object();
+    add_json_keyset(writer, "keys", &possible_keys);
+  }
+
   writer->add_member("table").start_object();
 
   writer->add_member("table_name").add_str(table_name);
   // partitions
   writer->add_member("access_type").add_str(join_type_str[type]);
-  if (!possible_keys.is_empty())
-  {
-    List_iterator_fast<char> it(possible_keys);
-    const char *name;
-    writer->add_member("possible_keys").start_array();
-    while ((name= it++))
-      writer->add_str(name);
-    writer->end_array();
-  }
+
+  add_json_keyset(writer, "possible_keys", &possible_keys);
 
   /* `key` */
   /* For non-basic quick select, 'key' will not be present */
@@ -1271,10 +1288,13 @@ void Explain_table_access::print_explain_json(Explain_query *query,
   {
     tag_to_json(writer, extra_tags.at(i));
   }
+  
+  if (range_checked_fer)
+    writer->end_object(); // "range-checked-for-each-record"
 
   if (bka_type.is_using_jbuf())
   {
-    writer->end_object();
+    writer->end_object(); // "block-nl-join"
     writer->add_member("buffer_type").add_str(bka_type.incremental?
                                               "incremental":"flat");
     writer->add_member("join_type").add_str(bka_type.join_alg);
@@ -1388,7 +1408,7 @@ void Explain_table_access::append_tag_name(String *str, enum explain_extra_tag t
       char buf[MAX_KEY / 4 + 1];
       str->append(STRING_WITH_LEN("Range checked for each "
                                    "record (index map: 0x"));
-      str->append(range_checked_map.print(buf));
+      str->append(range_checked_fer->keys_map.print(buf));
       str->append(')');
       break;
     }

sql/sql_explain.h

@@ -538,6 +538,18 @@ private:
 };
 
 
+/*
+  Data structure for "range checked for each record". 
+  It's a set of keys, tabular explain prints hex bitmap, json prints key names.
+*/
+
+class Explain_range_checked_fer : public Sql_alloc
+{
+public:
+  String_list key_set;
+  key_map keys_map;
+};
+
 /*
   EXPLAIN data structure for a single JOIN_TAB.
 */
@@ -549,6 +561,7 @@ public:
     derived_select_number(0),
     non_merged_sjm_number(0),
     extra_tags(root),
+    range_checked_fer(NULL),
     start_dups_weedout(false),
     end_dups_weedout(false),
     where_cond(NULL),
@@ -618,9 +631,9 @@ public:
 
   // Valid if ET_USING tag is present
   Explain_quick_select *quick_info;
-
-  // valid with ET_RANGE_CHECKED_FOR_EACH_RECORD
-  key_map range_checked_map;
+  
+  /* Non-NULL values means this tab uses "range checked for each record" */
+  Explain_range_checked_fer *range_checked_fer;
 
   // valid with ET_USING_JOIN_BUFFER
   EXPLAIN_BKA_TYPE bka_type;

sql/sql_select.cc

@@ -23574,7 +23574,10 @@ void JOIN_TAB::save_explain_data(Explain_table_access *eta, table_map prefix_tab
       if (tab->use_quick == 2)
       {
         eta->push_extra(ET_RANGE_CHECKED_FOR_EACH_RECORD);
-        eta->range_checked_map= tab->keys;
+        eta->range_checked_fer= new (thd->mem_root) Explain_range_checked_fer;
+        eta->range_checked_fer->keys_map= tab->keys;
+        append_possible_keys(thd->mem_root, eta->range_checked_fer->key_set,
+                             table, tab->keys);
       }
       else if (tab->select->cond ||
                (tab->cache_select && tab->cache_select->cond))