Fixed bug mdev-3979.

Made allocation of memory for statistical data in a table share to be thread safe.
This memory is now allocated in a special MEM_ROOT that is created for each
table share.  

sql/sql_base.cc

@@ -3143,16 +3143,6 @@ retry_share:
     while (table_cache_count > table_cache_size && unused_tables)
       free_cache_entry(unused_tables);
 
-    if (get_use_stat_tables_mode(thd) > NEVER)
-    {
-      if (share->table_category != TABLE_CATEGORY_SYSTEM)
-      {
-        if (!share->stats_can_be_read && 
-            !alloc_statistics_for_table_share(thd, share, TRUE))
-	  share->stats_can_be_read= TRUE;
-      }
-    }
-
     mysql_mutex_unlock(&LOCK_open);
 
     /* make a new table */
@@ -4638,10 +4628,13 @@ open_and_process_table(THD *thd, LEX *lex, TABLE_LIST *tables,
   if (get_use_stat_tables_mode(thd) > NEVER && tables->table)
   {
     TABLE_SHARE *table_share= tables->table->s;
-    if (table_share && table_share->table_category != TABLE_CATEGORY_SYSTEM)
+    if (table_share && table_share->table_category == TABLE_CATEGORY_USER &&
+        table_share->tmp_table == NO_TMP_TABLE)
     {
-      if (!table_share->stats_can_be_read && 
+      if (table_share->stats_cb.stats_can_be_read ||
 	  !alloc_statistics_for_table_share(thd, table_share, FALSE))
+      {
+        if (table_share->stats_cb.stats_can_be_read)
         {   
           KEY *key_info= table_share->key_info;
           KEY *key_info_end= key_info + table_share->keys;
@@ -4652,8 +4645,7 @@ open_and_process_table(THD *thd, LEX *lex, TABLE_LIST *tables,
           Field **table_field_ptr= tables->table->field;
           for ( ; *field_ptr; field_ptr++, table_field_ptr++)
             (*table_field_ptr)->read_stats= (*field_ptr)->read_stats;
-  
-	table_share->stats_can_be_read= TRUE;
+        }
       }	
     }
   }
@@ -4895,7 +4887,7 @@ bool open_tables(THD *thd, TABLE_LIST **start, uint *counter, uint flags,
   }
 
   /*
-    Initialize temporary MEM_ROOT for new .FRM parsing. Do not allocate
+    Initialize temporary MEM_ROOT for new .FRM parsing. Do not alloctaate
     anything yet, to avoid penalty for statements which don't use views
     and thus new .FRM format.
   */

sql/sql_statistics.h

@@ -102,6 +102,7 @@ class Table_statistics
 public:
   my_bool cardinality_is_null;      /* TRUE if the cardinality is unknown */
   ha_rows cardinality;              /* Number of rows in the table        */
+  uchar *min_max_record_buffers;    /* Record buffers for min/max values  */
   Column_statistics *column_stats;  /* Array of statistical data for columns */
   Index_statistics *index_stats;    /* Array of statistical data for indexes */
   ulong *idx_avg_frequency;   /* Array of records per key for index prefixes */                                       

sql/table.cc

@@ -340,6 +340,8 @@ TABLE_SHARE *alloc_table_share(TABLE_LIST *table_list, char *key,
     share->free_tables.empty();
     share->m_flush_tickets.empty();
 
+    init_sql_alloc(&share->stats_cb.mem_root, TABLE_ALLOC_BLOCK_SIZE, 0);
+
     memcpy((char*) &share->mem_root, (char*) &mem_root, sizeof(mem_root));
     mysql_mutex_init(key_TABLE_SHARE_LOCK_ha_data,
                      &share->LOCK_ha_data, MY_MUTEX_INIT_FAST);
@@ -420,6 +422,14 @@ void TABLE_SHARE::destroy()
   uint idx;
   KEY *info_it;
 
+  if (tmp_table == NO_TMP_TABLE)
+    mysql_mutex_lock(&LOCK_ha_data);
+  free_root(&stats_cb.mem_root, MYF(0));
+  stats_cb.stats_can_be_read= FALSE;
+  stats_cb.stats_is_read= FALSE;
+  if (tmp_table == NO_TMP_TABLE)
+    mysql_mutex_unlock(&LOCK_ha_data);
+
   /* The mutex is initialized only for shares that are part of the TDC */
   if (tmp_table == NO_TMP_TABLE)
     mysql_mutex_destroy(&LOCK_ha_data);

sql/table.h

@@ -547,6 +547,21 @@ typedef I_P_List <Wait_for_flush,
                  Wait_for_flush_list;
 
 
+/**
+  Control block to access table statistics loaded 
+  from persistent statistical tables
+*/
+
+struct TABLE_STATISTICS_CB
+{
+  MEM_ROOT  mem_root; /* MEM_ROOT to allocate statistical data for the table */
+  Table_statistics *table_stats; /* Structure to access the statistical data */
+  bool stats_can_be_read;        /* Memory for statistical data is allocated */
+  bool stats_is_read;            /* Statistical data for table has been read
+                                    from statistical tables */   
+};
+
+
 /**
   This structure is shared between different table objects. There is one
   instance of table share per one table in the database.
@@ -585,14 +600,7 @@ struct TABLE_SHARE
   KEY  *key_info;			/* data of keys in database */
   uint	*blob_field;			/* Index to blobs in Field arrray*/
 
-  bool stats_can_be_read;      /* Memory for statistical data is allocated */
-  bool stats_is_read;          /* Statistical data for table has been read
-                                  from statistical tables */   
-  /*
-    This structure is used for statistical data on the table
-    that has been read from the statistical table table_stat
-  */ 
-  Table_statistics *read_stats;
+  TABLE_STATISTICS_CB stats_cb;
 
   uchar	*default_values;		/* row with default values */
   LEX_STRING comment;			/* Comment about table */