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Implemented MDEV-3941: CREATE TABLE xxx IF NOT EXISTS should not block if table exists.

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- Added option to check_if_table_exists() to quickly check if table exists (either SHARE or .FRM)
- Extended lock_table_names() to not wait for meta data locks if CREATE IF NOT EXISTS is used.

mysql-test/r/create.result:
  New test case
mysql-test/t/create.test:
  New test case
sql/sql_base.cc:
  Added option to check_if_table_exists() to quickly check if table exists (either SHARE or .FRM)
  Extended lock_table_names() to not wait for meta data locks if CREATE IF NOT EXISTS is used.
sql/sql_base.h:
  Updated prototype
sql/sql_db.cc:
  Added extra argument to call to check_if_table_exists()
This commit is contained in:
Michael Widenius 2012-12-16 16:13:17 +02:00
parent a6a8f12fa3
commit 33f3a11e2d
5 changed files with 111 additions and 14 deletions
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18
mysql-test/r/create.result
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@ -2403,3 +2403,21 @@ a b
1 1
drop table t1;
#
# Checking that CREATE IF NOT EXISTS is not blocked by running SELECT
#
create table t1 (a int, b int) engine=myisam;
create table t2 (a int, b int) engine=myisam;
insert into t1 values (1,1);
lock tables t1 read;
set @@lock_wait_timeout=5;
create table if not exists t1 (a int, b int);
ERROR 42S01: Table 't1' already exists
create table if not exists t1 (a int, b int) select 2,2;
ERROR 42S01: Table 't1' already exists
create table if not exists t1 like t2;
ERROR 42S01: Table 't1' already exists
select * from t1;
a b
1 1
unlock tables;
drop table t1,t2;

21
mysql-test/t/create.test
View File

@ -1996,4 +1996,25 @@ create table if not exists t1 (a int unique, b int)
ignore select 1 as a, 1 as b union select 1 as a, 2 as b;
select * from t1;
drop table t1;
--echo #
--echo # Checking that CREATE IF NOT EXISTS is not blocked by running SELECT
--echo #
create table t1 (a int, b int) engine=myisam;
create table t2 (a int, b int) engine=myisam;
insert into t1 values (1,1);
lock tables t1 read;
connect (user1,localhost,root,,test);
set @@lock_wait_timeout=5;
--error ER_TABLE_EXISTS_ERROR
create table if not exists t1 (a int, b int);
--error ER_TABLE_EXISTS_ERROR
create table if not exists t1 (a int, b int) select 2,2;
--error ER_TABLE_EXISTS_ERROR
create table if not exists t1 like t2;
disconnect user1;
connection default;
select * from t1;
unlock tables;
drop table t1,t2;

81
sql/sql_base.cc
View File

@ -2400,10 +2400,11 @@ void drop_open_table(THD *thd, TABLE *table, const char *db_name,
Check that table exists in table definition cache, on disk
or in some storage engine.
@param thd Thread context
@param table Table list element
@param[out] exists Out parameter which is set to TRUE if table
exists and to FALSE otherwise.
@param thd Thread context
@param table Table list element
@param fast_check Check only if share or .frm file exists
@param[out] exists Out parameter which is set to TRUE if table
exists and to FALSE otherwise.
@note This function acquires LOCK_open internally.
@ -2415,7 +2416,8 @@ void drop_open_table(THD *thd, TABLE *table, const char *db_name,
@retval FALSE No error. 'exists' out parameter set accordingly.
*/
bool check_if_table_exists(THD *thd, TABLE_LIST *table, bool *exists)
bool check_if_table_exists(THD *thd, TABLE_LIST *table, bool fast_check,
bool *exists)
{
char path[FN_REFLEN + 1];
TABLE_SHARE *share;
@ -2423,7 +2425,8 @@ bool check_if_table_exists(THD *thd, TABLE_LIST *table, bool *exists)
*exists= TRUE;
DBUG_ASSERT(thd->mdl_context.
DBUG_ASSERT(fast_check ||
thd->mdl_context.
is_lock_owner(MDL_key::TABLE, table->db,
table->table_name, MDL_SHARED));
@ -2440,6 +2443,12 @@ bool check_if_table_exists(THD *thd, TABLE_LIST *table, bool *exists)
if (!access(path, F_OK))
goto end;
if (fast_check)
{
*exists= FALSE;
goto end;
}
/* .FRM file doesn't exist. Check if some engine can provide it. */
if (ha_check_if_table_exists(thd, table->db, table->table_name, exists))
{
@ -2989,7 +2998,7 @@ bool open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
{
bool exists;
if (check_if_table_exists(thd, table_list, &exists))
if (check_if_table_exists(thd, table_list, 0, &exists))
DBUG_RETURN(TRUE);
if (!exists)
@ -4673,6 +4682,12 @@ extern "C" uchar *schema_set_get_key(const uchar *record, size_t *length,
@retval FALSE Success.
@retval TRUE Failure (e.g. connection was killed)
@notes
In case of CREATE TABLE IF NOT EXISTS we avoid a wait for tables that
are in use by first trying to do a meta data lock with timeout= 0.
If we get a timeout we will check if table exists (it should) and
retry with normal timeout if it didn't exists.
*/
bool
@ -4684,6 +4699,9 @@ lock_table_names(THD *thd,
TABLE_LIST *table;
MDL_request global_request;
Hash_set<TABLE_LIST, schema_set_get_key> schema_set;
ulong org_lock_wait_timeout= lock_wait_timeout;
/* Check if we are using CREATE TABLE ... IF NOT EXISTS */
bool create_if_not_exists;
DBUG_ENTER("lock_table_names");
DBUG_ASSERT(!thd->locked_tables_mode);
@ -4705,8 +4723,14 @@ lock_table_names(THD *thd,
}
}
if (! (flags & MYSQL_OPEN_SKIP_SCOPED_MDL_LOCK) &&
! mdl_requests.is_empty())
if (mdl_requests.is_empty())
DBUG_RETURN(FALSE);
/* Check if CREATE TABLE IF NOT EXISTS was used */
create_if_not_exists= (tables_start && tables_start->open_strategy ==
TABLE_LIST::OPEN_IF_EXISTS);
if (!(flags & MYSQL_OPEN_SKIP_SCOPED_MDL_LOCK))
{
/*
Scoped locks: Take intention exclusive locks on all involved
@ -4734,12 +4758,45 @@ lock_table_names(THD *thd,
global_request.init(MDL_key::GLOBAL, "", "", MDL_INTENTION_EXCLUSIVE,
MDL_STATEMENT);
mdl_requests.push_front(&global_request);
if (create_if_not_exists)
lock_wait_timeout= 0; // Don't wait for timeout
}
if (thd->mdl_context.acquire_locks(&mdl_requests, lock_wait_timeout))
DBUG_RETURN(TRUE);
for (;;)
{
bool exists= TRUE;
if (!thd->mdl_context.acquire_locks(&mdl_requests, lock_wait_timeout))
DBUG_RETURN(FALSE); // Got locks
DBUG_RETURN(FALSE);
if (!create_if_not_exists)
DBUG_RETURN(TRUE); // Return original error
/*
We come here in the case of lock timeout when executing
CREATE TABLE IF NOT EXISTS.
Verify that table really exists (it should as we got a lock conflict)
*/
if (check_if_table_exists(thd, tables_start, 1, &exists))
DBUG_RETURN(TRUE); // Should never happen
thd->clear_error(); // Forget timeout error
if (exists)
{
my_error(ER_TABLE_EXISTS_ERROR, MYF(0), tables_start->table_name);
DBUG_RETURN(TRUE);
}
/* purecov: begin inspected */
/*
We got error from acquire_locks but table didn't exists.
In theory this should never happen, except maybe in
CREATE or DROP DATABASE scenario.
We play safe and restart the original acquire_locks with the
orginal timeout
*/
create_if_not_exists= 0;
lock_wait_timeout= org_lock_wait_timeout;
/* purecov: end */
}
}

3
sql/sql_base.h
View File

@ -302,7 +302,8 @@ TABLE *find_table_for_mdl_upgrade(THD *thd, const char *db,
const char *table_name,
bool no_error);
void mark_tmp_table_for_reuse(TABLE *table);
bool check_if_table_exists(THD *thd, TABLE_LIST *table, bool *exists);
bool check_if_table_exists(THD *thd, TABLE_LIST *table, bool fast_check,
bool *exists);
int update_virtual_fields(THD *thd, TABLE *table,
enum enum_vcol_update_mode vcol_update_mode= VCOL_UPDATE_FOR_READ);
int dynamic_column_error_message(enum_dyncol_func_result rc);

2
sql/sql_db.cc
View File

@ -927,7 +927,7 @@ update_binlog:
char quoted_name[FN_REFLEN+3];
// Only write drop table to the binlog for tables that no longer exist.
if (check_if_table_exists(thd, tbl, &exists))
if (check_if_table_exists(thd, tbl, 0, &exists))
{
error= true;
goto exit;