MDEV-22910: SIGSEGV in Opt_trace_context::is_started & SIGSEGV in...

MDEV-22910: SIGSEGV in Opt_trace_context::is_started & SIGSEGV in Json_writer::add_table_name (on optimized builds)

Make sure to initialize members of TABLE::reginfo when TABLE::init is called. In this case the problem
was that table->reginfo.join_tab was set for the SELECT query and then was reused by the UPDATE query.
This case occurred only when the SELECT query had a degenerate join.

mysql-test/main/opt_trace.result

@@ -8559,5 +8559,36 @@ JSON_DETAILED(JSON_EXTRACT(trace, '$**.selectivity_for_columns'))
     ]
 ]
 drop table t1;
+#
+# MDEV-22910:SIGSEGV in Opt_trace_context::is_started & SIGSEGV in Json_writer::add_table_name
+# (on optimized builds)
+#
+CREATE TABLE t1( a INT, b INT, PRIMARY KEY( a ) );
+SELECT sum(b), row_number() OVER (order by b) FROM t1 WHERE a = 101;
+sum(b)	row_number() OVER (order by b)
+NULL	1
+UPDATE t1 SET b=10 WHERE a=1;
+SELECT JSON_DETAILED(JSON_EXTRACT(trace, '$**.range_scan_alternatives')) from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
+JSON_DETAILED(JSON_EXTRACT(trace, '$**.range_scan_alternatives'))
+[
+    
+    [
+        
+        {
+            "index": "PRIMARY",
+            "ranges": 
+            [
+                "(1) <= (a) <= (1)"
+            ],
+            "rowid_ordered": true,
+            "using_mrr": false,
+            "index_only": false,
+            "rows": 0,
+            "cost": 1.125,
+            "chosen": true
+        }
+    ]
+]
+DROP TABLE t1;
 set optimizer_trace='enabled=off';
 # End of 10.4 tests

mysql-test/main/opt_trace.test

@@ -611,5 +611,16 @@ EXPLAIN EXTENDED SELECT * from t1 WHERE b >= 10 and b < 25;
 select JSON_DETAILED(JSON_EXTRACT(trace, '$**.selectivity_for_columns')) from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
 drop table t1;
 
+--echo #
+--echo # MDEV-22910:SIGSEGV in Opt_trace_context::is_started & SIGSEGV in Json_writer::add_table_name
+--echo # (on optimized builds)
+--echo #
+
+CREATE TABLE t1( a INT, b INT, PRIMARY KEY( a ) );
+SELECT sum(b), row_number() OVER (order by b) FROM t1 WHERE a = 101;
+UPDATE t1 SET b=10 WHERE a=1;
+SELECT JSON_DETAILED(JSON_EXTRACT(trace, '$**.range_scan_alternatives')) from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
+DROP TABLE t1;
+
 set optimizer_trace='enabled=off';
 --echo # End of 10.4 tests

sql/opt_range.cc

@@ -2690,10 +2690,8 @@ int SQL_SELECT::test_quick_select(THD *thd, key_map keys_to_use,
   DBUG_PRINT("info",("Time to scan table: %g", read_time));
 
   Json_writer_object table_records(thd);
-  if (head->reginfo.join_tab)
-    table_records.add_table_name(head->reginfo.join_tab);
-  else
-    table_records.add_table_name(head);
+  table_records.add_table_name(head);
+
   Json_writer_object trace_range(thd, "range_analysis");
   {
     Json_writer_object table_rec(thd, "table_scan");

sql/table.cc

@@ -5160,6 +5160,8 @@ void TABLE::init(THD *thd, TABLE_LIST *tl)
   fulltext_searched= 0;
   file->ft_handler= 0;
   reginfo.impossible_range= 0;
+  reginfo.join_tab= NULL;
+  reginfo.not_exists_optimize= FALSE;
   created= TRUE;
   cond_selectivity= 1.0;
   cond_selectivity_sampling_explain= NULL;