diff options
Diffstat (limited to 'sql/set_var.cc')
| -rw-r--r-- | sql/set_var.cc | 66 |
1 files changed, 65 insertions, 1 deletions
diff --git a/sql/set_var.cc b/sql/set_var.cc index 2fe839189a0..cf8751bb895 100644 --- a/sql/set_var.cc +++ b/sql/set_var.cc @@ -369,7 +369,7 @@ sys_var_thd_ulong sys_preload_buff_size("preload_buffer_size", &SV::preload_buff_size); sys_var_thd_ulong sys_read_buff_size("read_buffer_size", &SV::read_buff_size); -sys_var_bool_ptr sys_readonly("read_only", &opt_readonly); +sys_var_opt_readonly sys_readonly("read_only", &opt_readonly); sys_var_thd_ulong sys_read_rnd_buff_size("read_rnd_buffer_size", &SV::read_rnd_buff_size); sys_var_thd_ulong sys_div_precincrement("div_precision_increment", @@ -3856,6 +3856,70 @@ bool sys_var_trust_routine_creators::update(THD *thd, set_var *var) return sys_var_bool_ptr::update(thd, var); } +bool sys_var_opt_readonly::update(THD *thd, set_var *var) +{ + bool result; + + DBUG_ENTER("sys_var_opt_readonly::update"); + + /* Prevent self dead-lock */ + if (thd->locked_tables || thd->active_transaction()) + { + my_error(ER_LOCK_OR_ACTIVE_TRANSACTION, MYF(0)); + DBUG_RETURN(true); + } + + if (thd->global_read_lock) + { + /* + This connection already holds the global read lock. + This can be the case with: + - FLUSH TABLES WITH READ LOCK + - SET GLOBAL READ_ONLY = 1 + */ + result= sys_var_bool_ptr::update(thd, var); + DBUG_RETURN(result); + } + + /* + Perform a 'FLUSH TABLES WITH READ LOCK'. + This is a 3 step process: + - [1] lock_global_read_lock() + - [2] close_cached_tables() + - [3] make_global_read_lock_block_commit() + [1] prevents new connections from obtaining tables locked for write. + [2] waits until all existing connections close their tables. + [3] prevents transactions from being committed. + */ + + if (lock_global_read_lock(thd)) + DBUG_RETURN(true); + + /* + This call will be blocked by any connection holding a READ or WRITE lock. + Ideally, we want to wait only for pending WRITE locks, but since: + con 1> LOCK TABLE T FOR READ; + con 2> LOCK TABLE T FOR WRITE; (blocked by con 1) + con 3> SET GLOBAL READ ONLY=1; (blocked by con 2) + can cause to wait on a read lock, it's required for the client application + to unlock everything, and acceptable for the server to wait on all locks. + */ + if (close_cached_tables(thd, true, NULL, false)) + goto end_with_read_lock; + + if (result= make_global_read_lock_block_commit(thd)) + goto end_with_read_lock; + + /* Change the opt_readonly system variable, safe because the lock is held */ + result= sys_var_bool_ptr::update(thd, var); + +end_with_read_lock: + /* Release the lock */ + unlock_global_read_lock(thd); + DBUG_RETURN(result); +} + + /* even session variable here requires SUPER, because of -#o,file */ bool sys_var_thd_dbug::check(THD *thd, set_var *var) { |