MDEV-22014: Rowid Filtering is not displayed well in the optimizer trace

- Print the rowid filters that are available for use with each table.
- Make print_best_access_for_table() print which filter it has picked.
- Make best_access_path() print the filter for considered ref accesses.

mysql-test/main/opt_trace_index_merge.result

@@ -217,8 +217,7 @@ explain select * from t1 where a=1 or b=1	{
                     "type": "index_merge",
                     "records": 2,
                     "cost": 4.1484,
-                    "uses_join_buffering": false,
-                    "filter_used": false
+                    "uses_join_buffering": false
                   }
                 },
                 "rows_for_plan": 2,

mysql-test/main/opt_trace_index_merge_innodb.result

@@ -171,6 +171,16 @@ explain select * from t1 where pk1 != 0  and key1 = 1	{
                   }
                 }
               },
+              {
+                "table": "t1",
+                "rowid_filters": [
+                  {
+                    "key": "key1",
+                    "build_cost": 1.1801,
+                    "rows": 1
+                  }
+                ]
+              },
               {
                 "selectivity_for_indexes": [
                   {
@@ -212,8 +222,7 @@ explain select * from t1 where pk1 != 0  and key1 = 1	{
                     "type": "ref",
                     "records": 1,
                     "cost": 2,
-                    "uses_join_buffering": false,
-                    "filter_used": false
+                    "uses_join_buffering": false
                   }
                 },
                 "rows_for_plan": 1,

mysql-test/main/opt_trace_security.result

@@ -103,8 +103,7 @@ select * from db1.t1	{
                     "type": "scan",
                     "records": 3,
                     "cost": 2.0051,
-                    "uses_join_buffering": false,
-                    "filter_used": false
+                    "uses_join_buffering": false
                   }
                 },
                 "rows_for_plan": 3,
@@ -227,8 +226,7 @@ select * from db1.v1	{
                     "type": "scan",
                     "records": 3,
                     "cost": 2.0051,
-                    "uses_join_buffering": false,
-                    "filter_used": false
+                    "uses_join_buffering": false
                   }
                 },
                 "rows_for_plan": 3,

sql/opt_trace.cc

@@ -24,6 +24,8 @@
 #include "my_json_writer.h"
 #include "sp_head.h"
 
+#include "rowid_filter.h"
+
 const char I_S_table_name[]= "OPTIMIZER_TRACE";
 
 /**
@@ -661,14 +663,17 @@ void print_best_access_for_table(THD *thd, POSITION *pos,
 {
   DBUG_ASSERT(thd->trace_started());
 
-  Json_writer_object trace_best_access(thd, "chosen_access_method");
-  trace_best_access.add("type", type == JT_ALL ? "scan" :
-                                                 join_type_str[type]);
-  trace_best_access.add("records", pos->records_read);
-  trace_best_access.add("cost", pos->read_time);
-  trace_best_access.add("uses_join_buffering", pos->use_join_buffer);
-  trace_best_access.add("filter_used",
-                         pos->range_rowid_filter_info != NULL);
+  Json_writer_object obj(thd, "chosen_access_method");
+  obj.add("type", type == JT_ALL ? "scan" : join_type_str[type]);
+  obj.add("records", pos->records_read);
+  obj.add("cost", pos->read_time);
+  obj.add("uses_join_buffering", pos->use_join_buffer);
+  if (pos->range_rowid_filter_info)
+  {
+    uint key_no= pos->range_rowid_filter_info->key_no;
+    obj.add("rowid_filter_key",
+            pos->table->table->key_info[key_no].name);
+  }
 }
 
 

sql/rowid_filter.cc

@@ -20,6 +20,7 @@
 #include "opt_range.h"
 #include "rowid_filter.h"
 #include "sql_select.h"
+#include "opt_trace.h"
 
 
 inline
@@ -403,9 +404,37 @@ void TABLE::init_cost_info_for_usable_range_rowid_filters(THD *thd)
   }
 
   prune_range_rowid_filters();
+
+  if (unlikely(thd->trace_started()))
+    trace_range_rowid_filters(thd);
 }
 
 
+void TABLE::trace_range_rowid_filters(THD *thd) const
+{
+  if (!range_rowid_filter_cost_info_elems)
+    return;
+
+  Range_rowid_filter_cost_info **p= range_rowid_filter_cost_info_ptr;
+  Range_rowid_filter_cost_info **end= p + range_rowid_filter_cost_info_elems;
+
+  Json_writer_object js_obj(thd);
+  js_obj.add_table_name(this);
+  Json_writer_array js_arr(thd, "rowid_filters");
+
+  for (; p < end; p++)
+    (*p)->trace_info(thd);
+}
+
+
+void Range_rowid_filter_cost_info::trace_info(THD *thd)
+{
+  Json_writer_object js_obj(thd);
+  js_obj.add("key", table->key_info[key_no].name);
+  js_obj.add("build_cost", b);
+  js_obj.add("rows", est_elements);
+}
+
 /**
   @brief
     Choose the best range filter for the given access of the table

sql/rowid_filter.h

@@ -452,6 +452,8 @@ public:
 
   double get_a() { return a; }
 
+  void trace_info(THD *thd);
+
   friend
   void TABLE::prune_range_rowid_filters();
 

sql/sql_select.cc

@@ -7758,6 +7758,8 @@ best_access_path(JOIN      *join,
           filter->get_cmp_gain(rows);
           tmp-= filter->get_adjusted_gain(rows) - filter->get_cmp_gain(rows);
           DBUG_ASSERT(tmp >= 0);
+          trace_access_idx.add("rowid_filter_key",
+                               s->table->key_info[filter->key_no].name);
         }
       }
       trace_access_idx.add("rows", records).add("cost", tmp);

sql/table.h

@@ -1566,6 +1566,7 @@ public:
 
   void init_cost_info_for_usable_range_rowid_filters(THD *thd);
   void prune_range_rowid_filters();
+  void trace_range_rowid_filters(THD *thd) const;
   Range_rowid_filter_cost_info *
   best_range_rowid_filter_for_partial_join(uint access_key_no,
                                            double records,