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.

mysql-test/r/stat_tables.result

@@ -524,3 +524,31 @@ SELECT CONVERT_TZ( '1991-09-20 10:11:02', '+00:00', 'GMT' );
 CONVERT_TZ( '1991-09-20 10:11:02', '+00:00', 'GMT' )
 NULL
 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	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
+test	t1	t	NULL	NULL	0.0000	3.0000	NULL	NULL	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
+SELECT pk FROM t1;
+pk
+1
+2
+DROP TABLE t1;
+set use_stat_tables=@save_use_stat_tables;

mysql-test/r/stat_tables_innodb.result

@@ -551,5 +551,33 @@ SELECT CONVERT_TZ( '1991-09-20 10:11:02', '+00:00', 'GMT' );
 CONVERT_TZ( '1991-09-20 10:11:02', '+00:00', 'GMT' )
 NULL
 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	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
+test	t1	t	NULL	NULL	0.0000	3.0000	NULL	NULL	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
+SELECT pk FROM t1;
+pk
+1
+2
+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

@@ -312,3 +312,27 @@ drop table t1;
 SET use_stat_tables = PREFERABLY;
 SELECT CONVERT_TZ( '1991-09-20 10:11:02', '+00:00', 'GMT' );
 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

@@ -2916,6 +2916,39 @@ 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

@@ -89,6 +89,7 @@ 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 "hash.h"
 #include "table.h"
 #include "sql_base.h"
+#include "sql_statistics.h"
 
 /** Configuration. */
 ulong tdc_size; /**< Table definition cache threshold for LRU eviction. */
@@ -869,6 +870,7 @@ void tdc_release_share(TABLE_SHARE *share)
   mysql_mutex_lock(&share->tdc.LOCK_table_share);
   if (share->tdc.flushed)
   {
+    delete_stat_values_for_table_share(share);
     mysql_mutex_unlock(&share->tdc.LOCK_table_share);
     mysql_mutex_unlock(&LOCK_unused_shares);
     tdc_delete_share_from_hash(share);