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------------------------------------------------------------
revno: 2630.4.33
committer: Dmitry Lenev <dlenev@mysql.com>
branch nick: mysql-6.0-3726-w2
timestamp: Fri 2008-06-20 17:11:20 +0400
message:
  WL#3726 "DDL locking for all metadata objects".

  After-review fixes in progress.

  Minimized dependency of mdl.cc on other modules (particularly
  made it independant of mysql_priv.h) in order to be able
  write unit tests for metadata locking subsystem.
This commit is contained in:
Konstantin Osipov 2009-12-02 19:31:57 +03:00
parent 0a49fd92d9
commit edddfa0ef4
8 changed files with 120 additions and 55 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
sql/ha_ndbcluster_binlog.cc
View File

@ -141,7 +141,7 @@ static Uint64 *p_latest_trans_gci= 0;
static TABLE *ndb_binlog_index= 0; static TABLE *ndb_binlog_index= 0;
static TABLE_LIST binlog_tables; static TABLE_LIST binlog_tables;
static MDL_LOCK_DATA binlog_mdl_lock_data; static MDL_LOCK_DATA binlog_mdl_lock_data;
static char binlog_mdlkey[MAX_DBKEY_LENGTH]; static char binlog_mdlkey[MAX_MDLKEY_LENGTH];
/* /*
Helper functions Helper functions

2
sql/log_event.cc
View File

@ -8074,7 +8074,7 @@ int Table_map_log_event::do_apply_event(Relay_log_info const *rli)
&db_mem, (uint) NAME_LEN + 1, &db_mem, (uint) NAME_LEN + 1,
&tname_mem, (uint) NAME_LEN + 1, &tname_mem, (uint) NAME_LEN + 1,
&mdl_lock_data, sizeof(MDL_LOCK_DATA), &mdl_lock_data, sizeof(MDL_LOCK_DATA),
&mdlkey, MAX_DBKEY_LENGTH, &mdlkey, MAX_MDLKEY_LENGTH,
NullS))) NullS)))
DBUG_RETURN(HA_ERR_OUT_OF_MEM); DBUG_RETURN(HA_ERR_OUT_OF_MEM);

136
sql/mdl.cc
View File

@ -15,13 +15,9 @@
/*
TODO: Remove this dependency on mysql_priv.h. It's not
trivial step at the moment since currently we access to
some of THD members and use some of its methods here.
*/
#include "mysql_priv.h"
#include "mdl.h" #include "mdl.h"
#include <hash.h>
#include <mysqld_error.h>
/** /**
@ -308,7 +304,7 @@ MDL_LOCK_DATA *mdl_alloc_lock(int type, const char *db, const char *name,
char *key; char *key;
if (!multi_alloc_root(root, &lock_data, sizeof(MDL_LOCK_DATA), &key, if (!multi_alloc_root(root, &lock_data, sizeof(MDL_LOCK_DATA), &key,
MAX_DBKEY_LENGTH, NULL)) MAX_MDLKEY_LENGTH, NULL))
return NULL; return NULL;
mdl_init_lock(lock_data, key, type, db, name); mdl_init_lock(lock_data, key, type, db, name);
@ -441,6 +437,58 @@ static bool is_shared(MDL_LOCK_DATA *lock_data)
} }
/**
Helper functions and macros to be used for killable waiting in metadata
locking subsystem.
@sa THD::enter_cond()/exit_cond()/killed.
@note We can't use THD::enter_cond()/exit_cond()/killed directly here
since this will make metadata subsystem dependant on THD class
and thus prevent us from writing unit tests for it. And usage of
wrapper functions to access THD::killed/enter_cond()/exit_cond()
will probably introduce too much overhead.
*/
#define MDL_ENTER_COND(A, B) mdl_enter_cond(A, B, __func__, __FILE__, __LINE__)
static inline const char* mdl_enter_cond(MDL_CONTEXT *context,
st_my_thread_var *mysys_var,
const char *calling_func,
const char *calling_file,
const unsigned int calling_line)
{
safe_mutex_assert_owner(&LOCK_mdl);
mysys_var->current_mutex= &LOCK_mdl;
mysys_var->current_cond= &COND_mdl;
return set_thd_proc_info(context->thd, "Waiting for table",
calling_func, calling_file, calling_line);
}
#define MDL_EXIT_COND(A, B, C) mdl_exit_cond(A, B, C, __func__, __FILE__, __LINE__)
static inline void mdl_exit_cond(MDL_CONTEXT *context,
st_my_thread_var *mysys_var,
const char* old_msg,
const char *calling_func,
const char *calling_file,
const unsigned int calling_line)
{
DBUG_ASSERT(&LOCK_mdl == mysys_var->current_mutex);
pthread_mutex_unlock(&LOCK_mdl);
pthread_mutex_lock(&mysys_var->mutex);
mysys_var->current_mutex= 0;
mysys_var->current_cond= 0;
pthread_mutex_unlock(&mysys_var->mutex);
(void) set_thd_proc_info(context->thd, old_msg, calling_func,
calling_file, calling_line);
}
/** /**
Check if request for the lock on particular object can be satisfied given Check if request for the lock on particular object can be satisfied given
current state of the global metadata lock. current state of the global metadata lock.
@ -752,9 +800,7 @@ bool mdl_acquire_exclusive_locks(MDL_CONTEXT *context)
bool signalled= FALSE; bool signalled= FALSE;
const char *old_msg; const char *old_msg;
I_P_List_iterator<MDL_LOCK_DATA, MDL_LOCK_DATA_context> it(context->locks); I_P_List_iterator<MDL_LOCK_DATA, MDL_LOCK_DATA_context> it(context->locks);
THD *thd= context->thd; st_my_thread_var *mysys_var= my_thread_var;
DBUG_ASSERT(thd == current_thd);
safe_mutex_assert_not_owner(&LOCK_open); safe_mutex_assert_not_owner(&LOCK_open);
@ -766,7 +812,7 @@ bool mdl_acquire_exclusive_locks(MDL_CONTEXT *context)
pthread_mutex_lock(&LOCK_mdl); pthread_mutex_lock(&LOCK_mdl);
old_msg= thd->enter_cond(&COND_mdl, &LOCK_mdl, "Waiting for table"); old_msg= MDL_ENTER_COND(context, mysys_var);
while ((lock_data= it++)) while ((lock_data= it++))
{ {
@ -826,8 +872,11 @@ bool mdl_acquire_exclusive_locks(MDL_CONTEXT *context)
!lock->active_shared_waiting_upgrade.is_empty(); !lock->active_shared_waiting_upgrade.is_empty();
while ((conf_lock_data= it++)) while ((conf_lock_data= it++))
{
signalled|= signalled|=
notify_thread_having_shared_lock(thd, conf_lock_data->ctx->thd); mysql_notify_thread_having_shared_lock(context->thd,
conf_lock_data->ctx->thd);
}
break; break;
} }
@ -848,7 +897,7 @@ bool mdl_acquire_exclusive_locks(MDL_CONTEXT *context)
set_timespec(abstime, 10); set_timespec(abstime, 10);
pthread_cond_timedwait(&COND_mdl, &LOCK_mdl, &abstime); pthread_cond_timedwait(&COND_mdl, &LOCK_mdl, &abstime);
} }
if (thd->killed) if (mysys_var->abort)
goto err; goto err;
} }
it.rewind(); it.rewind();
@ -863,8 +912,8 @@ bool mdl_acquire_exclusive_locks(MDL_CONTEXT *context)
(*lock->cached_object_release_hook)(lock->cached_object); (*lock->cached_object_release_hook)(lock->cached_object);
lock->cached_object= NULL; lock->cached_object= NULL;
} }
/* As a side-effect THD::exit_cond() unlocks LOCK_mdl. */ /* As a side-effect MDL_EXIT_COND() unlocks LOCK_mdl. */
thd->exit_cond(old_msg); MDL_EXIT_COND(context, mysys_var, old_msg);
return FALSE; return FALSE;
err: err:
@ -880,7 +929,7 @@ err:
} }
/* May be some pending requests for shared locks can be satisfied now. */ /* May be some pending requests for shared locks can be satisfied now. */
pthread_cond_broadcast(&COND_mdl); pthread_cond_broadcast(&COND_mdl);
thd->exit_cond(old_msg); MDL_EXIT_COND(context, mysys_var, old_msg);
return TRUE; return TRUE;
} }
@ -907,12 +956,10 @@ bool mdl_upgrade_shared_lock_to_exclusive(MDL_CONTEXT *context,
{ {
MDL_LOCK *lock; MDL_LOCK *lock;
const char *old_msg; const char *old_msg;
THD *thd= context->thd; st_my_thread_var *mysys_var= my_thread_var;
DBUG_ENTER("mdl_upgrade_shared_lock_to_exclusive"); DBUG_ENTER("mdl_upgrade_shared_lock_to_exclusive");
DBUG_ASSERT(thd == current_thd);
safe_mutex_assert_not_owner(&LOCK_open); safe_mutex_assert_not_owner(&LOCK_open);
DBUG_ASSERT(lock_data->state == MDL_ACQUIRED); DBUG_ASSERT(lock_data->state == MDL_ACQUIRED);
@ -927,7 +974,7 @@ bool mdl_upgrade_shared_lock_to_exclusive(MDL_CONTEXT *context,
pthread_mutex_lock(&LOCK_mdl); pthread_mutex_lock(&LOCK_mdl);
old_msg= thd->enter_cond(&COND_mdl, &LOCK_mdl, "Waiting for table"); old_msg= MDL_ENTER_COND(context, mysys_var);
lock_data->state= MDL_PENDING_UPGRADE; lock_data->state= MDL_PENDING_UPGRADE;
/* Set type of lock request to the type at which we are aiming. */ /* Set type of lock request to the type at which we are aiming. */
@ -960,8 +1007,11 @@ bool mdl_upgrade_shared_lock_to_exclusive(MDL_CONTEXT *context,
while ((conf_lock_data= it++)) while ((conf_lock_data= it++))
{ {
if (conf_lock_data->ctx != context) if (conf_lock_data->ctx != context)
signalled|= notify_thread_having_shared_lock(thd, {
conf_lock_data->ctx->thd); signalled|=
mysql_notify_thread_having_shared_lock(context->thd,
conf_lock_data->ctx->thd);
}
} }
if (signalled) if (signalled)
@ -979,7 +1029,7 @@ bool mdl_upgrade_shared_lock_to_exclusive(MDL_CONTEXT *context,
DBUG_PRINT("info", ("Failed to wake-up from table-level lock ... sleeping")); DBUG_PRINT("info", ("Failed to wake-up from table-level lock ... sleeping"));
pthread_cond_timedwait(&COND_mdl, &LOCK_mdl, &abstime); pthread_cond_timedwait(&COND_mdl, &LOCK_mdl, &abstime);
} }
if (thd->killed) if (mysys_var->abort)
{ {
lock_data->state= MDL_ACQUIRED; lock_data->state= MDL_ACQUIRED;
lock_data->type= MDL_SHARED_UPGRADABLE; lock_data->type= MDL_SHARED_UPGRADABLE;
@ -987,7 +1037,7 @@ bool mdl_upgrade_shared_lock_to_exclusive(MDL_CONTEXT *context,
lock->active_shared.push_front(lock_data); lock->active_shared.push_front(lock_data);
/* Pending requests for shared locks can be satisfied now. */ /* Pending requests for shared locks can be satisfied now. */
pthread_cond_broadcast(&COND_mdl); pthread_cond_broadcast(&COND_mdl);
thd->exit_cond(old_msg); MDL_EXIT_COND(context, mysys_var, old_msg);
DBUG_RETURN(TRUE); DBUG_RETURN(TRUE);
} }
} }
@ -999,8 +1049,8 @@ bool mdl_upgrade_shared_lock_to_exclusive(MDL_CONTEXT *context,
(*lock->cached_object_release_hook)(lock->cached_object); (*lock->cached_object_release_hook)(lock->cached_object);
lock->cached_object= 0; lock->cached_object= 0;
/* As a side-effect THD::exit_cond() unlocks LOCK_mdl. */ /* As a side-effect MDL_EXIT_COND() unlocks LOCK_mdl. */
thd->exit_cond(old_msg); MDL_EXIT_COND(context, mysys_var, old_msg);
DBUG_RETURN(FALSE); DBUG_RETURN(FALSE);
} }
@ -1086,32 +1136,31 @@ err:
bool mdl_acquire_global_shared_lock(MDL_CONTEXT *context) bool mdl_acquire_global_shared_lock(MDL_CONTEXT *context)
{ {
THD *thd= context->thd; st_my_thread_var *mysys_var= my_thread_var;
const char *old_msg; const char *old_msg;
safe_mutex_assert_not_owner(&LOCK_open); safe_mutex_assert_not_owner(&LOCK_open);
DBUG_ASSERT(thd == current_thd);
DBUG_ASSERT(!context->has_global_shared_lock); DBUG_ASSERT(!context->has_global_shared_lock);
pthread_mutex_lock(&LOCK_mdl); pthread_mutex_lock(&LOCK_mdl);
global_lock.waiting_shared++; global_lock.waiting_shared++;
old_msg= thd->enter_cond(&COND_mdl, &LOCK_mdl, "Waiting for table"); old_msg= MDL_ENTER_COND(context, mysys_var);
while (!thd->killed && global_lock.active_intention_exclusive) while (!mysys_var->abort && global_lock.active_intention_exclusive)
pthread_cond_wait(&COND_mdl, &LOCK_mdl); pthread_cond_wait(&COND_mdl, &LOCK_mdl);
global_lock.waiting_shared--; global_lock.waiting_shared--;
if (thd->killed) if (mysys_var->abort)
{ {
/* As a side-effect THD::exit_cond() unlocks LOCK_mdl. */ /* As a side-effect MDL_EXIT_COND() unlocks LOCK_mdl. */
thd->exit_cond(old_msg); MDL_EXIT_COND(context, mysys_var, old_msg);
return TRUE; return TRUE;
} }
global_lock.active_shared++; global_lock.active_shared++;
context->has_global_shared_lock= TRUE; context->has_global_shared_lock= TRUE;
/* As a side-effect THD::exit_cond() unlocks LOCK_mdl. */ /* As a side-effect MDL_EXIT_COND() unlocks LOCK_mdl. */
thd->exit_cond(old_msg); MDL_EXIT_COND(context, mysys_var, old_msg);
return FALSE; return FALSE;
} }
@ -1137,12 +1186,11 @@ bool mdl_wait_for_locks(MDL_CONTEXT *context)
MDL_LOCK *lock; MDL_LOCK *lock;
I_P_List_iterator<MDL_LOCK_DATA, MDL_LOCK_DATA_context> it(context->locks); I_P_List_iterator<MDL_LOCK_DATA, MDL_LOCK_DATA_context> it(context->locks);
const char *old_msg; const char *old_msg;
THD *thd= context->thd; st_my_thread_var *mysys_var= my_thread_var;
safe_mutex_assert_not_owner(&LOCK_open); safe_mutex_assert_not_owner(&LOCK_open);
DBUG_ASSERT(thd == current_thd);
while (!thd->killed) while (!mysys_var->abort)
{ {
/* /*
We have to check if there are some HANDLERs open by this thread We have to check if there are some HANDLERs open by this thread
@ -1156,7 +1204,7 @@ bool mdl_wait_for_locks(MDL_CONTEXT *context)
*/ */
mysql_ha_flush(context->thd); mysql_ha_flush(context->thd);
pthread_mutex_lock(&LOCK_mdl); pthread_mutex_lock(&LOCK_mdl);
old_msg= thd->enter_cond(&COND_mdl, &LOCK_mdl, "Waiting for table"); old_msg= MDL_ENTER_COND(context, mysys_var);
it.rewind(); it.rewind();
while ((lock_data= it++)) while ((lock_data= it++))
{ {
@ -1179,10 +1227,10 @@ bool mdl_wait_for_locks(MDL_CONTEXT *context)
break; break;
} }
pthread_cond_wait(&COND_mdl, &LOCK_mdl); pthread_cond_wait(&COND_mdl, &LOCK_mdl);
/* As a side-effect THD::exit_cond() unlocks LOCK_mdl. */ /* As a side-effect MDL_EXIT_COND() unlocks LOCK_mdl. */
thd->exit_cond(old_msg); MDL_EXIT_COND(context, mysys_var, old_msg);
} }
return thd->killed; return mysys_var->abort;
} }
@ -1422,7 +1470,7 @@ void mdl_release_global_shared_lock(MDL_CONTEXT *context)
bool mdl_is_exclusive_lock_owner(MDL_CONTEXT *context, int type, bool mdl_is_exclusive_lock_owner(MDL_CONTEXT *context, int type,
const char *db, const char *name) const char *db, const char *name)
{ {
char key[MAX_DBKEY_LENGTH]; char key[MAX_MDLKEY_LENGTH];
uint key_length; uint key_length;
MDL_LOCK_DATA *lock_data; MDL_LOCK_DATA *lock_data;
I_P_List_iterator<MDL_LOCK_DATA, MDL_LOCK_DATA_context> it(context->locks); I_P_List_iterator<MDL_LOCK_DATA, MDL_LOCK_DATA_context> it(context->locks);
@ -1456,7 +1504,7 @@ bool mdl_is_exclusive_lock_owner(MDL_CONTEXT *context, int type,
bool mdl_is_lock_owner(MDL_CONTEXT *context, int type, const char *db, bool mdl_is_lock_owner(MDL_CONTEXT *context, int type, const char *db,
const char *name) const char *name)
{ {
char key[MAX_DBKEY_LENGTH]; char key[MAX_MDLKEY_LENGTH];
uint key_length; uint key_length;
MDL_LOCK_DATA *lock_data; MDL_LOCK_DATA *lock_data;
I_P_List_iterator<MDL_LOCK_DATA, MDL_LOCK_DATA_context> it(context->locks); I_P_List_iterator<MDL_LOCK_DATA, MDL_LOCK_DATA_context> it(context->locks);

19
sql/mdl.h
View File

@ -19,6 +19,7 @@
#include "sql_plist.h" #include "sql_plist.h"
#include <my_sys.h> #include <my_sys.h>
#include <m_string.h> #include <m_string.h>
#include <mysql_com.h>
class THD; class THD;
@ -148,6 +149,9 @@ void mdl_context_backup_and_reset(MDL_CONTEXT *ctx, MDL_CONTEXT *backup);
void mdl_context_restore(MDL_CONTEXT *ctx, MDL_CONTEXT *backup); void mdl_context_restore(MDL_CONTEXT *ctx, MDL_CONTEXT *backup);
void mdl_context_merge(MDL_CONTEXT *target, MDL_CONTEXT *source); void mdl_context_merge(MDL_CONTEXT *target, MDL_CONTEXT *source);
/** Maximal length of key for metadata locking subsystem. */
#define MAX_MDLKEY_LENGTH (4 + NAME_LEN + 1 + NAME_LEN + 1)
void mdl_init_lock(MDL_LOCK_DATA *lock_data, char *key, int type, void mdl_init_lock(MDL_LOCK_DATA *lock_data, char *key, int type,
const char *db, const char *name); const char *db, const char *name);
MDL_LOCK_DATA *mdl_alloc_lock(int type, const char *db, const char *name, MDL_LOCK_DATA *mdl_alloc_lock(int type, const char *db, const char *name,
@ -237,4 +241,19 @@ void* mdl_get_cached_object(MDL_LOCK_DATA *lock_data);
void mdl_set_cached_object(MDL_LOCK_DATA *lock_data, void *cached_object, void mdl_set_cached_object(MDL_LOCK_DATA *lock_data, void *cached_object,
mdl_cached_object_release_hook release_hook); mdl_cached_object_release_hook release_hook);
/*
Functions in the server's kernel used by metadata locking subsystem.
*/
extern bool mysql_notify_thread_having_shared_lock(THD *thd, THD *in_use);
extern void mysql_ha_flush(THD *thd);
extern "C" const char *set_thd_proc_info(THD *thd, const char *info,
const char *calling_function,
const char *calling_file,
const unsigned int calling_line);
#ifndef DBUG_OFF
extern pthread_mutex_t LOCK_open;
#endif
#endif #endif

2
sql/mysql_priv.h
View File

@ -1534,8 +1534,6 @@ char *generate_partition_syntax(partition_info *part_info,
Alter_info *alter_info); Alter_info *alter_info);
#endif #endif
bool notify_thread_having_shared_lock(THD *thd, THD *in_use);
enum enum_tdc_remove_table_type {TDC_RT_REMOVE_ALL, TDC_RT_REMOVE_NOT_OWN, enum enum_tdc_remove_table_type {TDC_RT_REMOVE_ALL, TDC_RT_REMOVE_NOT_OWN,
TDC_RT_REMOVE_UNUSED}; TDC_RT_REMOVE_UNUSED};
void tdc_remove_table(THD *thd, enum_tdc_remove_table_type remove_type, void tdc_remove_table(THD *thd, enum_tdc_remove_table_type remove_type,

8
sql/sql_base.cc
View File

@ -1275,7 +1275,7 @@ close_all_tables_for_name(THD *thd, TABLE_SHARE *share,
/* /*
We need to hold LOCK_open while changing the open_tables We need to hold LOCK_open while changing the open_tables
list, since another thread may work on it. list, since another thread may work on it.
@sa notify_thread_having_shared_lock() @sa mysql_notify_thread_having_shared_lock()
*/ */
pthread_mutex_lock(&LOCK_open); pthread_mutex_lock(&LOCK_open);
@ -1455,7 +1455,7 @@ void close_thread_tables(THD *thd,
/* /*
Note that we need to hold LOCK_open while changing the Note that we need to hold LOCK_open while changing the
open_tables list. Another thread may work on it. open_tables list. Another thread may work on it.
(See: notify_thread_having_shared_lock()) (See: mysql_notify_thread_having_shared_lock())
Closing a MERGE child before the parent would be fatal if the Closing a MERGE child before the parent would be fatal if the
other thread tries to abort the MERGE lock in between. other thread tries to abort the MERGE lock in between.
*/ */
@ -7956,7 +7956,7 @@ void flush_tables()
rest of the server is broken. rest of the server is broken.
*/ */
bool notify_thread_having_shared_lock(THD *thd, THD *in_use) bool mysql_notify_thread_having_shared_lock(THD *thd, THD *in_use)
{ {
bool signalled= FALSE; bool signalled= FALSE;
if ((in_use->system_thread & SYSTEM_THREAD_DELAYED_INSERT) && if ((in_use->system_thread & SYSTEM_THREAD_DELAYED_INSERT) &&
@ -8501,7 +8501,7 @@ void close_performance_schema_table(THD *thd, Open_tables_state *backup)
/* /*
Note that we need to hold LOCK_open while changing the Note that we need to hold LOCK_open while changing the
open_tables list. Another thread may work on it. open_tables list. Another thread may work on it.
(See: notify_thread_having_shared_lock()) (See: mysql_notify_thread_having_shared_lock())
Closing a MERGE child before the parent would be fatal if the Closing a MERGE child before the parent would be fatal if the
other thread tries to abort the MERGE lock in between. other thread tries to abort the MERGE lock in between.
*/ */

2
sql/sql_handler.cc
View File

@ -247,7 +247,7 @@ bool mysql_ha_open(THD *thd, TABLE_LIST *tables, bool reopen)
&name, (uint) namelen, &name, (uint) namelen,
&alias, (uint) aliaslen, &alias, (uint) aliaslen,
&mdl_lock_data, sizeof(MDL_LOCK_DATA), &mdl_lock_data, sizeof(MDL_LOCK_DATA),
&mdlkey, MAX_DBKEY_LENGTH, &mdlkey, MAX_MDLKEY_LENGTH,
NullS))) NullS)))
{ {
DBUG_PRINT("exit",("ERROR")); DBUG_PRINT("exit",("ERROR"));

4
sql/sql_show.cc
View File

@ -3084,7 +3084,7 @@ uint get_table_open_method(TABLE_LIST *tables,
@param mdlkey Pointer to the buffer for key for the lock request @param mdlkey Pointer to the buffer for key for the lock request
(should be at least strlen(db) + strlen(name) + 2 (should be at least strlen(db) + strlen(name) + 2
bytes, or, if the lengths are not known, bytes, or, if the lengths are not known,
MAX_DBNAME_LENGTH) MAX_MDLKEY_LENGTH)
@param table Table list element for the table @param table Table list element for the table
@note This is an auxiliary function to be used in cases when we want to @note This is an auxiliary function to be used in cases when we want to
@ -3157,7 +3157,7 @@ static int fill_schema_table_from_frm(THD *thd,TABLE *table,
uint key_length; uint key_length;
char db_name_buff[NAME_LEN + 1], table_name_buff[NAME_LEN + 1]; char db_name_buff[NAME_LEN + 1], table_name_buff[NAME_LEN + 1];
MDL_LOCK_DATA mdl_lock_data; MDL_LOCK_DATA mdl_lock_data;
char mdlkey[MAX_DBKEY_LENGTH]; char mdlkey[MAX_MDLKEY_LENGTH];
bzero((char*) &table_list, sizeof(TABLE_LIST)); bzero((char*) &table_list, sizeof(TABLE_LIST));
bzero((char*) &tbl, sizeof(TABLE)); bzero((char*) &tbl, sizeof(TABLE));