Fix Bug #18559 "log tables cannot change engine, and

gets deadlocked when dropping w/ log on"

Log tables rely on concurrent insert machinery to add data.
This means that log tables are always opened and locked by
special (artificial) logger threads. Because of this, the thread
which tries to drop a log table starts to wait for the table
to be unlocked. Which will happen only if the log table is disabled.
Alike situation happens if one tries to alter a log table.
However in addition to the problem above, alter table calls
check_if_locking_is_allowed() routine for the engine. The
routine does not allow alter for the log tables. So, alter
doesn't start waiting forever for logs to be disabled, but 
returns with an error.
Another problem is that not all engines could be used for
the log tables. That's because they need concurrent insert.

In this patch we:
(1) Explicitly disallow to drop/alter a log table if it
    is currently used by the logger.
(2) Update MyISAM to support log tables
(3) Allow to drop log tables/alter log tables if log is
    disabled
At the same time we (4) Disallow to alter log tables to
unsupported engine (after this patch CSV and MyISAM are 
alowed)
Recommit with review fixes.

mysql-test/r/log_tables.result

@@ -72,3 +72,144 @@ sleep(2)
 select * from mysql.slow_log;
 start_time	user_host	query_time	lock_time	rows_sent	rows_examined	db	last_insert_id	insert_id	server_id	sql_text
 TIMESTAMP	USER_HOST	QUERY_TIME	00:00:00	1	0	test	0	0	1	select sleep(2)
+alter table mysql.general_log engine=myisam;
+ERROR HY000: You can't alter a log table if logging is enabled
+alter table mysql.slow_log engine=myisam;
+ERROR HY000: You can't alter a log table if logging is enabled
+drop table mysql.general_log;
+ERROR HY000: Cannot drop log table if log is enabled
+drop table mysql.slow_log;
+ERROR HY000: Cannot drop log table if log is enabled
+set global general_log='OFF';
+alter table mysql.slow_log engine=myisam;
+ERROR HY000: You can't alter a log table if logging is enabled
+set global slow_query_log='OFF';
+show create table mysql.general_log;
+Table	Create Table
+general_log	CREATE TABLE `general_log` (
+  `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  `user_host` mediumtext,
+  `thread_id` int(11) DEFAULT NULL,
+  `server_id` int(11) DEFAULT NULL,
+  `command_type` varchar(64) DEFAULT NULL,
+  `argument` mediumtext
+) ENGINE=CSV DEFAULT CHARSET=utf8 COMMENT='General log'
+show create table mysql.slow_log;
+Table	Create Table
+slow_log	CREATE TABLE `slow_log` (
+  `start_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  `user_host` mediumtext NOT NULL,
+  `query_time` time NOT NULL,
+  `lock_time` time NOT NULL,
+  `rows_sent` int(11) NOT NULL,
+  `rows_examined` int(11) NOT NULL,
+  `db` varchar(512) DEFAULT NULL,
+  `last_insert_id` int(11) DEFAULT NULL,
+  `insert_id` int(11) DEFAULT NULL,
+  `server_id` int(11) DEFAULT NULL,
+  `sql_text` mediumtext NOT NULL
+) ENGINE=CSV DEFAULT CHARSET=utf8 COMMENT='Slow log'
+alter table mysql.general_log engine=myisam;
+alter table mysql.slow_log engine=myisam;
+Warnings:
+Warning	1264	Out of range value for column 'last_insert_id' at row 0
+Warning	1264	Out of range value for column 'insert_id' at row 0
+show create table mysql.general_log;
+Table	Create Table
+general_log	CREATE TABLE `general_log` (
+  `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  `user_host` mediumtext,
+  `thread_id` int(11) DEFAULT NULL,
+  `server_id` int(11) DEFAULT NULL,
+  `command_type` varchar(64) DEFAULT NULL,
+  `argument` mediumtext
+) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='General log'
+show create table mysql.slow_log;
+Table	Create Table
+slow_log	CREATE TABLE `slow_log` (
+  `start_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  `user_host` mediumtext NOT NULL,
+  `query_time` time NOT NULL,
+  `lock_time` time NOT NULL,
+  `rows_sent` int(11) NOT NULL,
+  `rows_examined` int(11) NOT NULL,
+  `db` varchar(512) DEFAULT NULL,
+  `last_insert_id` int(11) DEFAULT NULL,
+  `insert_id` int(11) DEFAULT NULL,
+  `server_id` int(11) DEFAULT NULL,
+  `sql_text` mediumtext NOT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=utf8 COMMENT='Slow log'
+set global general_log='ON';
+set global slow_query_log='ON';
+select * from mysql.general_log;
+event_time	user_host	thread_id	server_id	command_type	argument
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	set names utf8
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	create table bug16905 (s char(15) character set utf8 default 'пусто')
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	insert into bug16905 values ('новое')
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	select * from mysql.general_log
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	drop table bug16905
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	truncate table mysql.slow_log
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	set session long_query_time=1
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	select sleep(2)
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	select * from mysql.slow_log
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	alter table mysql.general_log engine=myisam
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	alter table mysql.slow_log engine=myisam
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	drop table mysql.general_log
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	drop table mysql.slow_log
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	set global general_log='OFF'
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	set global slow_query_log='ON'
+TIMESTAMP	USER_HOST	THREAD_ID	1	Query	select * from mysql.general_log
+flush logs;
+lock tables mysql.general_log WRITE;
+ERROR HY000: You can't write-lock a log table. Only read access is possible.
+lock tables mysql.slow_log WRITE;
+ERROR HY000: You can't write-lock a log table. Only read access is possible.
+lock tables mysql.general_log READ;
+ERROR HY000: You can't use usual read lock with log tables. Try READ LOCAL instead.
+lock tables mysql.slow_log READ;
+ERROR HY000: You can't use usual read lock with log tables. Try READ LOCAL instead.
+lock tables mysql.slow_log READ LOCAL, mysql.general_log READ LOCAL;
+unlock tables;
+set global general_log='OFF';
+set global slow_query_log='OFF';
+alter table mysql.slow_log engine=ndb;
+ERROR HY000: One can use only CSV and MyISAM engines for the log tables
+alter table mysql.slow_log engine=innodb;
+ERROR HY000: One can use only CSV and MyISAM engines for the log tables
+alter table mysql.slow_log engine=archive;
+ERROR HY000: One can use only CSV and MyISAM engines for the log tables
+alter table mysql.slow_log engine=blackhole;
+ERROR HY000: One can use only CSV and MyISAM engines for the log tables
+drop table mysql.slow_log;
+drop table mysql.general_log;
+drop table mysql.general_log;
+ERROR 42S02: Unknown table 'general_log'
+drop table mysql.slow_log;
+ERROR 42S02: Unknown table 'slow_log'
+use mysql;
+CREATE TABLE `general_log` (
+`event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
+ON UPDATE CURRENT_TIMESTAMP,
+`user_host` mediumtext,
+`thread_id` int(11) DEFAULT NULL,
+`server_id` int(11) DEFAULT NULL,
+`command_type` varchar(64) DEFAULT NULL,
+`argument` mediumtext
+) ENGINE=CSV DEFAULT CHARSET=utf8 COMMENT='General log';
+CREATE TABLE `slow_log` (
+`start_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
+ON UPDATE CURRENT_TIMESTAMP,
+`user_host` mediumtext NOT NULL,
+`query_time` time NOT NULL,
+`lock_time` time NOT NULL,
+`rows_sent` int(11) NOT NULL,
+`rows_examined` int(11) NOT NULL,
+`db` varchar(512) DEFAULT NULL,
+`last_insert_id` int(11) DEFAULT NULL,
+`insert_id` int(11) DEFAULT NULL,
+`server_id` int(11) DEFAULT NULL,
+`sql_text` mediumtext NOT NULL
+) ENGINE=CSV DEFAULT CHARSET=utf8 COMMENT='Slow log';
+set global general_log='ON';
+set global slow_query_log='ON';
+use test;

mysql-test/t/log_tables.test

@@ -171,6 +171,139 @@ select sleep(2);
 --replace_column 1 TIMESTAMP 2 USER_HOST 3 QUERY_TIME
 select * from mysql.slow_log;
 
+#
+# Bug #18559 log tables cannot change engine, and gets deadlocked when
+# dropping w/ log on
+#
+
+# check that appropriate error messages are given when one attempts to alter
+# or drop a log tables, while corresponding logs are enabled
+--error ER_CANT_ALTER_LOG_TABLE
+alter table mysql.general_log engine=myisam;
+--error ER_CANT_ALTER_LOG_TABLE
+alter table mysql.slow_log engine=myisam;
+
+--error ER_CANT_DROP_LOG_TABLE
+drop table mysql.general_log;
+--error ER_CANT_DROP_LOG_TABLE
+drop table mysql.slow_log;
+
+# check that one can alter log tables to MyISAM
+set global general_log='OFF';
+
+# cannot convert another log table
+--error ER_CANT_ALTER_LOG_TABLE
+alter table mysql.slow_log engine=myisam;
+
+# alter both tables
+set global slow_query_log='OFF';
+# check that both tables use CSV engine
+show create table mysql.general_log;
+show create table mysql.slow_log;
+
+alter table mysql.general_log engine=myisam;
+alter table mysql.slow_log engine=myisam;
+
+# check that the tables were converted
+show create table mysql.general_log;
+show create table mysql.slow_log;
+
+# enable log tables and chek that new tables indeed work
+set global general_log='ON';
+set global slow_query_log='ON';
+
+--replace_column 1 TIMESTAMP 2 USER_HOST 3 THREAD_ID
+select * from mysql.general_log;
+
+# check that flush of myisam-based log tables work fine
+flush logs;
+
+# check locking of myisam-based log tables
+
+--error ER_CANT_WRITE_LOCK_LOG_TABLE
+lock tables mysql.general_log WRITE;
+
+--error ER_CANT_WRITE_LOCK_LOG_TABLE
+lock tables mysql.slow_log WRITE;
+
+#
+# This attemts to get TL_READ_NO_INSERT lock, which is incompatible with
+# TL_WRITE_CONCURRENT_INSERT. This should fail. We issue this error as log
+# tables are always opened and locked by the logger.
+#
+
+--error ER_CANT_READ_LOCK_LOG_TABLE
+lock tables mysql.general_log READ;
+
+--error ER_CANT_READ_LOCK_LOG_TABLE
+lock tables mysql.slow_log READ;
+
+#
+# This call should result in TL_READ lock on the log table. This is ok and
+# should pass.
+#
+
+lock tables mysql.slow_log READ LOCAL, mysql.general_log READ LOCAL;
+
+unlock tables;
+
+# check that we can drop them
+set global general_log='OFF';
+set global slow_query_log='OFF';
+
+# check that alter table doesn't work for other engines
+--error ER_BAD_LOG_ENGINE
+alter table mysql.slow_log engine=ndb;
+--error ER_BAD_LOG_ENGINE
+alter table mysql.slow_log engine=innodb;
+--error ER_BAD_LOG_ENGINE
+alter table mysql.slow_log engine=archive;
+--error ER_BAD_LOG_ENGINE
+alter table mysql.slow_log engine=blackhole;
+
+drop table mysql.slow_log;
+drop table mysql.general_log;
+
+# check that table share cleanup is performed correctly (double drop)
+
+--error ER_BAD_TABLE_ERROR
+drop table mysql.general_log;
+--error ER_BAD_TABLE_ERROR
+drop table mysql.slow_log;
+
+# recreate tables and enable logs
+
+use mysql;
+
+CREATE TABLE `general_log` (
+  `event_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
+                         ON UPDATE CURRENT_TIMESTAMP,
+  `user_host` mediumtext,
+  `thread_id` int(11) DEFAULT NULL,
+  `server_id` int(11) DEFAULT NULL,
+  `command_type` varchar(64) DEFAULT NULL,
+  `argument` mediumtext
+) ENGINE=CSV DEFAULT CHARSET=utf8 COMMENT='General log';
+
+CREATE TABLE `slow_log` (
+  `start_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
+                         ON UPDATE CURRENT_TIMESTAMP,
+  `user_host` mediumtext NOT NULL,
+  `query_time` time NOT NULL,
+  `lock_time` time NOT NULL,
+  `rows_sent` int(11) NOT NULL,
+  `rows_examined` int(11) NOT NULL,
+  `db` varchar(512) DEFAULT NULL,
+  `last_insert_id` int(11) DEFAULT NULL,
+  `insert_id` int(11) DEFAULT NULL,
+  `server_id` int(11) DEFAULT NULL,
+  `sql_text` mediumtext NOT NULL
+) ENGINE=CSV DEFAULT CHARSET=utf8 COMMENT='Slow log';
+
+set global general_log='ON';
+set global slow_query_log='ON';
+use test;
+
 # kill all connections
 disconnect con1;
 disconnect con2;

sql/ha_myisam.cc

@@ -274,6 +274,15 @@ bool ha_myisam::check_if_locking_is_allowed(uint sql_command,
              table->s->table_name.str);
     return FALSE;
   }
+
+  /*
+    Deny locking of the log tables, which is incompatible with
+    concurrent insert. Unless called from a logger THD:
+    general_log_thd or slow_log_thd.
+  */
+  if (!called_by_logger_thread)
+    return check_if_log_table_locking_is_allowed(sql_command, type, table);
+
   return TRUE;
 }
 

sql/handler.cc

@@ -1422,6 +1422,34 @@ void handler::ha_statistic_increment(ulong SSV::*offset) const
   statistic_increment(table->in_use->status_var.*offset, &LOCK_status);
 }
 
+
+bool handler::check_if_log_table_locking_is_allowed(uint sql_command,
+                                                    ulong type, TABLE *table)
+{
+  /*
+    Deny locking of the log tables, which is incompatible with
+    concurrent insert. Unless called from a logger THD:
+    general_log_thd or slow_log_thd.
+  */
+  if (table->s->log_table &&
+      sql_command != SQLCOM_TRUNCATE &&
+      sql_command != SQLCOM_ALTER_TABLE &&
+      !(sql_command == SQLCOM_FLUSH &&
+        type & REFRESH_LOG) &&
+      (table->reginfo.lock_type >= TL_READ_NO_INSERT))
+  {
+    /*
+      The check  >= TL_READ_NO_INSERT denies all write locks
+      plus the only read lock (TL_READ_NO_INSERT itself)
+    */
+    table->reginfo.lock_type == TL_READ_NO_INSERT ?
+      my_error(ER_CANT_READ_LOCK_LOG_TABLE, MYF(0)) :
+        my_error(ER_CANT_WRITE_LOCK_LOG_TABLE, MYF(0));
+    return FALSE;
+  }
+  return TRUE;
+}
+
 /*
   Open database-handler.
 

sql/handler.h

@@ -974,6 +974,8 @@ public:
   {
     return TRUE;
   }
+  bool check_if_log_table_locking_is_allowed(uint sql_command,
+                                             ulong type, TABLE *table);
   int ha_open(TABLE *table, const char *name, int mode, int test_if_locked);
   void adjust_next_insert_id_after_explicit_value(ulonglong nr);
   bool update_auto_increment();

sql/log.cc

@@ -1106,15 +1106,16 @@ void Log_to_csv_event_handler::
   THD *log_thd, *curr= current_thd;
   TABLE_LIST *table;
 
-  if (!logger.is_log_tables_initialized)
-    return;                                     /* do nothing */
-
   switch (log_table_type) {
   case QUERY_LOG_GENERAL:
+    if (!logger.is_general_log_table_enabled())
+      return;                                     /* do nothing */
     log_thd= general_log_thd;
     table= &general_log;
     break;
   case QUERY_LOG_SLOW:
+    if (!logger.is_slow_log_table_enabled())
+      return;                                     /* do nothing */
     log_thd= slow_log_thd;
     table= &slow_log;
     break;

sql/log.h

@@ -497,6 +497,14 @@ public:
   {}
   void lock() { (void) pthread_mutex_lock(&LOCK_logger); }
   void unlock() { (void) pthread_mutex_unlock(&LOCK_logger); }
+  bool is_general_log_table_enabled()
+  {
+    return table_log_handler && table_log_handler->general_log.table != 0;
+  }
+  bool is_slow_log_table_enabled()
+  {
+    return table_log_handler && table_log_handler->slow_log.table != 0;
+  }
   /*
     We want to initialize all log mutexes as soon as possible,
     but we cannot do it in constructor, as safe_mutex relies on

sql/share/errmsg.txt

@@ -5841,3 +5841,9 @@ ER_RBR_NOT_AVAILABLE
         eng "The server was not built with row-based replication"
 ER_NO_TRIGGERS_ON_SYSTEM_SCHEMA
 	eng "Triggers can not be created on system tables"
+ER_CANT_ALTER_LOG_TABLE
+        eng "You can't alter a log table if logging is enabled"
+ER_BAD_LOG_ENGINE
+        eng "One can use only CSV and MyISAM engines for the log tables"
+ER_CANT_DROP_LOG_TABLE
+        eng "Cannot drop log table if log is enabled"

sql/sql_table.cc

@@ -1537,6 +1537,18 @@ int mysql_rm_table_part2(THD *thd, TABLE_LIST *tables, bool if_exists,
     table->db_type= NULL;
     if ((share= get_cached_table_share(table->db, table->table_name)))
       table->db_type= share->db_type;
+
+    /* Disable drop of enabled log tables */
+    if (share && share->log_table &&
+        ((!my_strcasecmp(system_charset_info, table->table_name,
+                         "general_log") && opt_log &&
+          logger.is_general_log_table_enabled()) ||
+         (!my_strcasecmp(system_charset_info, table->table_name, "slow_log")
+          && opt_slow_log && logger.is_slow_log_table_enabled())))
+    {
+      my_error(ER_CANT_DROP_LOG_TABLE, MYF(0));
+      DBUG_RETURN(1);
+    }
   }
 
   if (lock_table_names(thd, tables))
@@ -4991,6 +5003,42 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
   LINT_INIT(index_add_buffer);
   LINT_INIT(index_drop_buffer);
 
+  if (table_list && table_list->db &&
+      !my_strcasecmp(system_charset_info, table_list->db, "mysql") &&
+      table_list->table_name)
+  {
+    enum enum_table_kind { NOT_LOG_TABLE= 1, GENERAL_LOG, SLOW_LOG }
+         table_kind= NOT_LOG_TABLE;
+
+    if (!my_strcasecmp(system_charset_info, table_list->table_name,
+                       "general_log"))
+      table_kind= GENERAL_LOG;
+    else
+      if (!my_strcasecmp(system_charset_info, table_list->table_name,
+                         "slow_log"))
+        table_kind= SLOW_LOG;
+
+    /* Disable alter of enabled log tables */
+    if ((table_kind == GENERAL_LOG && opt_log &&
+        logger.is_general_log_table_enabled()) ||
+       (table_kind == SLOW_LOG && opt_slow_log &&
+         logger.is_slow_log_table_enabled()))
+    {
+      my_error(ER_CANT_ALTER_LOG_TABLE, MYF(0));
+      DBUG_RETURN(TRUE);
+    }
+
+    /* Disable alter of log tables to unsupported engine */
+    if ((table_kind == GENERAL_LOG || table_kind == SLOW_LOG) &&
+        (lex_create_info->used_fields & HA_CREATE_USED_ENGINE) &&
+        !(lex_create_info->db_type->db_type == DB_TYPE_MYISAM ||
+          lex_create_info->db_type->db_type == DB_TYPE_CSV_DB))
+    {
+      my_error(ER_BAD_LOG_ENGINE, MYF(0));
+      DBUG_RETURN(TRUE);
+    }
+  }
+
   thd->proc_info="init";
   if (!(create_info= copy_create_info(lex_create_info)))
   {

storage/csv/ha_tina.cc

@@ -817,27 +817,9 @@ bool ha_tina::check_if_locking_is_allowed(uint sql_command,
                                           uint count,
                                           bool called_by_logger_thread)
 {
-  /*
+  if (!called_by_logger_thread)
-    Deny locking of the log tables, which is incompatible with
+    return check_if_log_table_locking_is_allowed(sql_command, type, table);
-    concurrent insert. Unless called from a logger THD:
+
-    general_log_thd or slow_log_thd.
-  */
-  if (table->s->log_table &&
-      sql_command != SQLCOM_TRUNCATE &&
-      !(sql_command == SQLCOM_FLUSH &&
-        type & REFRESH_LOG) &&
-      !called_by_logger_thread &&
-      (table->reginfo.lock_type >= TL_READ_NO_INSERT))
-  {
-    /*
-      The check  >= TL_READ_NO_INSERT denies all write locks
-      plus the only read lock (TL_READ_NO_INSERT itself)
-    */
-    table->reginfo.lock_type == TL_READ_NO_INSERT ?
-      my_error(ER_CANT_READ_LOCK_LOG_TABLE, MYF(0)) :
-        my_error(ER_CANT_WRITE_LOCK_LOG_TABLE, MYF(0));
-    return FALSE;
-  }
   return TRUE;
 }
 

storage/myisam/mi_extra.c

@@ -366,6 +366,11 @@ int mi_extra(MI_INFO *info, enum ha_extra_function function, void *extra_arg)
     pthread_mutex_unlock(&share->intern_lock);
 #endif
     break;
+  case HA_EXTRA_MARK_AS_LOG_TABLE:
+    pthread_mutex_lock(&share->intern_lock);
+    share->is_log_table= TRUE;
+    pthread_mutex_unlock(&share->intern_lock);
+    break;
   case HA_EXTRA_KEY_CACHE:
   case HA_EXTRA_NO_KEY_CACHE:
   default:

storage/myisam/mi_open.c

@@ -489,6 +489,7 @@ MI_INFO *mi_open(const char *name, int mode, uint open_flags)
       share->data_file_type = DYNAMIC_RECORD;
     my_afree((gptr) disk_cache);
     mi_setup_functions(share);
+    share->is_log_table= FALSE;
 #ifdef THREAD
     thr_lock_init(&share->lock);
     VOID(pthread_mutex_init(&share->intern_lock,MY_MUTEX_INIT_FAST));

storage/myisam/mi_write.c

@@ -163,6 +163,18 @@ int mi_write(MI_INFO *info, byte *record)
     (*info->invalidator)(info->filename);
     info->invalidator=0;
   }
+
+  /*
+    Update status of the table. We need to do so after each row write
+    for the log tables, as we want the new row to become visible to
+    other threads as soon as possible. We lock mutex here to follow
+    pthread memory visibility rules.
+  */
+  pthread_mutex_lock(&share->intern_lock);
+  if (share->is_log_table)
+    mi_update_status((void*) info);
+  pthread_mutex_unlock(&share->intern_lock);
+
   allow_break();				/* Allow SIGHUP & SIGINT */
   DBUG_RETURN(0);
 

storage/myisam/myisamdef.h

@@ -201,6 +201,9 @@ typedef struct st_mi_isam_share {	/* Shared between opens */
   uint	blocksize;			/* blocksize of keyfile */
   myf write_flag;
   enum data_file_type data_file_type;
+  /* Below flag is needed to make log tables work with concurrent insert */
+  my_bool is_log_table;
+
   my_bool  changed,			/* If changed since lock */
     global_changed,			/* If changed since open */
     not_flushed,