MDEV-16757 Memory leak after adding manually min/max statistical data

for blob column

ANALYZE TABLE <table> does not collect statistical data on min/max values
for BLOB columns of <table>. However these values can be added into
mysql.column_stats manually by executing proper statements.
Unfortunately this led to a memory leak because the memory allocated
for these values was never freed.
This patch provides the server with a function to free memory allocated
for min/max statistical values of BLOB types.

Temporarily changed the test case until MDEV-16711 is fixed as without
this fix the test case for MDEV-16757 did not fail only for 10.0.

mysql-test/r/stat_tables.result

@@ -517,3 +517,27 @@ drop database db1;
 drop database db2;
 drop table t1;
 set use_stat_tables=@save_use_stat_tables;
+#
+# MDEV-16757: manual addition of min/max statistics for BLOB
+#
+SET use_stat_tables= PREFERABLY;
+CREATE TABLE t1 (pk INT PRIMARY KEY, t TEXT);
+INSERT INTO t1 VALUES (1,'foo'),(2,'bar');
+ANALYZE TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	Warning	Engine-independent statistics are not collected for column 't'
+test.t1	analyze	status	OK
+SELECT * FROM mysql.column_stats;
+db_name	table_name	column_name	min_value	max_value	nulls_ratio	avg_length	avg_frequency	hist_size	hist_type	histogram
+test	t1	pk	1	2	0.0000	4.0000	1.0000	0	NULL	NULL
+DELETE FROM mysql.column_stats
+WHERE db_name='test' AND table_name='t1' AND column_name='t';
+INSERT INTO mysql.column_stats VALUES
+('test','t1','t','bar','foo', 0.0, 3.0, 1.0, 0, NULL, NULL);
+SELECT * FROM mysql.column_stats;
+db_name	table_name	column_name	min_value	max_value	nulls_ratio	avg_length	avg_frequency	hist_size	hist_type	histogram
+test	t1	pk	1	2	0.0000	4.0000	1.0000	0	NULL	NULL
+test	t1	t	bar	foo	0.0000	3.0000	1.0000	0	NULL	NULL
+DROP TABLE t1;
+set use_stat_tables=@save_use_stat_tables;

mysql-test/r/stat_tables_innodb.result

@@ -544,5 +544,29 @@ drop database db1;
 drop database db2;
 drop table t1;
 set use_stat_tables=@save_use_stat_tables;
+#
+# MDEV-16757: manual addition of min/max statistics for BLOB
+#
+SET use_stat_tables= PREFERABLY;
+CREATE TABLE t1 (pk INT PRIMARY KEY, t TEXT);
+INSERT INTO t1 VALUES (1,'foo'),(2,'bar');
+ANALYZE TABLE t1;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	Warning	Engine-independent statistics are not collected for column 't'
+test.t1	analyze	status	OK
+SELECT * FROM mysql.column_stats;
+db_name	table_name	column_name	min_value	max_value	nulls_ratio	avg_length	avg_frequency	hist_size	hist_type	histogram
+test	t1	pk	1	2	0.0000	4.0000	1.0000	0	NULL	NULL
+DELETE FROM mysql.column_stats
+WHERE db_name='test' AND table_name='t1' AND column_name='t';
+INSERT INTO mysql.column_stats VALUES
+('test','t1','t','bar','foo', 0.0, 3.0, 1.0, 0, NULL, NULL);
+SELECT * FROM mysql.column_stats;
+db_name	table_name	column_name	min_value	max_value	nulls_ratio	avg_length	avg_frequency	hist_size	hist_type	histogram
+test	t1	pk	1	2	0.0000	4.0000	1.0000	0	NULL	NULL
+test	t1	t	bar	foo	0.0000	3.0000	1.0000	0	NULL	NULL
+DROP TABLE t1;
+set use_stat_tables=@save_use_stat_tables;
 set optimizer_switch=@save_optimizer_switch_for_stat_tables_test;
 SET SESSION STORAGE_ENGINE=DEFAULT;

mysql-test/t/stat_tables.test

@@ -306,3 +306,27 @@ drop database db2;
 drop table t1;
 
 set use_stat_tables=@save_use_stat_tables;
+
+--echo #
+--echo # MDEV-16757: manual addition of min/max statistics for BLOB
+--echo #
+
+SET use_stat_tables= PREFERABLY;
+
+CREATE TABLE t1 (pk INT PRIMARY KEY, t TEXT);
+INSERT INTO t1 VALUES (1,'foo'),(2,'bar');
+ANALYZE TABLE t1;
+--sorted_result
+SELECT * FROM mysql.column_stats;
+DELETE FROM mysql.column_stats
+  WHERE db_name='test' AND table_name='t1' AND column_name='t';
+INSERT INTO mysql.column_stats VALUES
+  ('test','t1','t','bar','foo', 0.0, 3.0, 1.0, 0, NULL, NULL);
+--sorted_result
+SELECT * FROM mysql.column_stats;
+
+# SELECT pk FROM t1;
+
+DROP TABLE t1;
+
+set use_stat_tables=@save_use_stat_tables;

sql/sql_statistics.cc

@@ -3055,6 +3055,39 @@ int read_statistics_for_table(THD *thd, TABLE *table, TABLE_LIST *stat_tables)
 }
 
 
+/**
+  @breif
+  Cleanup of min/max statistical values for table share
+*/
+
+void delete_stat_values_for_table_share(TABLE_SHARE *table_share)
+{
+  TABLE_STATISTICS_CB *stats_cb= &table_share->stats_cb;
+  Table_statistics *table_stats= stats_cb->table_stats;
+  if (!table_stats)
+    return;
+  Column_statistics *column_stats= table_stats->column_stats;
+  if (!column_stats)
+    return;
+
+  for (Field **field_ptr= table_share->field;
+       *field_ptr;
+       field_ptr++, column_stats++)
+  {
+    if (column_stats->min_value)
+    {
+      delete column_stats->min_value;
+      column_stats->min_value= NULL;
+    }
+    if (column_stats->max_value)
+    {
+      delete column_stats->max_value;
+      column_stats->max_value= NULL;
+    }
+  }
+}
+
+
 /**
   @brief
   Check whether any statistics is to be read for tables from a table list

sql/sql_statistics.h

@@ -92,6 +92,7 @@ int read_statistics_for_tables_if_needed(THD *thd, TABLE_LIST *tables);
 int collect_statistics_for_table(THD *thd, TABLE *table);
 int alloc_statistics_for_table_share(THD* thd, TABLE_SHARE *share,
                                      bool is_safe);
+void delete_stat_values_for_table_share(TABLE_SHARE *table_share);
 int alloc_statistics_for_table(THD *thd, TABLE *table);
 int update_statistics_for_table(THD *thd, TABLE *table);
 int delete_statistics_for_table(THD *thd, LEX_STRING *db, LEX_STRING *tab);

sql/table_cache.cc

@@ -52,6 +52,7 @@
 #include "lf.h"
 #include "table.h"
 #include "sql_base.h"
+#include "sql_statistics.h"
 
 
 /** Configuration. */
@@ -786,6 +787,7 @@ void tdc_release_share(TABLE_SHARE *share)
   }
   if (share->tdc->flushed || tdc_records() > tdc_size)
   {
+    delete_stat_values_for_table_share(share);
     mysql_mutex_unlock(&LOCK_unused_shares);
     tdc_delete_share_from_hash(share->tdc);
     DBUG_VOID_RETURN;