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c7bbd8917c
Bug#25422 (Hang with log tables)
Bug 17876 (Truncating mysql.slow_log in a SP after using cursor locks the
thread)
Bug 23044 (Warnings on flush of a log table)
Bug 29129 (Resetting general_log while the GLOBAL READ LOCK is set causes
a deadlock)
Prior to this fix, the server would hang when performing concurrent
ALTER TABLE or TRUNCATE TABLE statements against the LOG TABLES,
which are mysql.general_log and mysql.slow_log.
The root cause traces to the following code:
in sql_base.cc, open_table()
if (table->in_use != thd)
{
/* wait_for_condition will unlock LOCK_open for us */
wait_for_condition(thd, &LOCK_open, &COND_refresh);
}
The problem with this code is that the current implementation of the
LOGGER creates 'fake' THD objects, like
- Log_to_csv_event_handler::general_log_thd
- Log_to_csv_event_handler::slow_log_thd
which are not associated to a real thread running in the server,
so that waiting for these non-existing threads to release table locks
cause the dead lock.
In general, the design of Log_to_csv_event_handler does not fit into the
general architecture of the server, so that the concept of general_log_thd
and slow_log_thd has to be abandoned:
- this implementation does not work with table locking
- it will not work with commands like SHOW PROCESSLIST
- having the log tables always opened does not integrate well with DDL
operations / FLUSH TABLES / SET GLOBAL READ_ONLY
With this patch, the fundamental design of the LOGGER has been changed to:
- always open and close a log table when writing a log
- remove totally the usage of fake THD objects
- clarify how locking of log tables is implemented in general.
See WL#3984 for details related to the new locking design.
Additional changes (misc bugs exposed and fixed):
1)
mysqldump which would ignore some tables in dump_all_tables_in_db(),
but forget to ignore the same in dump_all_views_in_db().
2)
mysqldump would also issue an empty "LOCK TABLE" command when all the tables
to lock are to be ignored (numrows == 0), instead of not issuing the query.
3)
Internal errors handlers could intercept errors but not warnings
(see sql_error.cc).
4)
Implementing a nested call to open tables, for the performance schema tables,
exposed an existing bug in remove_table_from_cache(), which would perform:
in_use->some_tables_deleted=1;
against another thread, without any consideration about thread locking.
This call inside remove_table_from_cache() was not required anyway,
since calling mysql_lock_abort() takes care of aborting -- cleanly -- threads
that might hold a lock on a table.
This line (in_use->some_tables_deleted=1) has been removed.
118 lines
3.3 KiB
Text
118 lines
3.3 KiB
Text
flush status;
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show status like 'Table_lock%';
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Variable_name Value
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Table_locks_immediate 1
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Table_locks_waited 0
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select * from information_schema.session_status where variable_name like 'Table_lock%';
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VARIABLE_NAME VARIABLE_VALUE
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TABLE_LOCKS_IMMEDIATE 2
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TABLE_LOCKS_WAITED 0
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SET SQL_LOG_BIN=0;
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drop table if exists t1;
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create table t1(n int) engine=myisam;
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insert into t1 values(1);
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lock tables t1 read;
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unlock tables;
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lock tables t1 read;
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update t1 set n = 3;
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unlock tables;
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show status like 'Table_lock%';
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Variable_name Value
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Table_locks_immediate 17
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Table_locks_waited 1
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select * from information_schema.session_status where variable_name like 'Table_lock%';
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VARIABLE_NAME VARIABLE_VALUE
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TABLE_LOCKS_IMMEDIATE 18
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TABLE_LOCKS_WAITED 1
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drop table t1;
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select 1;
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1
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1
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show status like 'last_query_cost';
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Variable_name Value
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Last_query_cost 0.000000
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create table t1 (a int);
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insert into t1 values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10);
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insert into t1 values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10);
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insert into t1 values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10);
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insert into t1 values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10);
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insert into t1 values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10);
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select * from t1 where a=6;
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a
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6
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6
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6
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6
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6
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show status like 'last_query_cost';
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Variable_name Value
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Last_query_cost 12.084449
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show status like 'last_query_cost';
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Variable_name Value
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Last_query_cost 12.084449
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select 1;
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1
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1
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show status like 'last_query_cost';
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Variable_name Value
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Last_query_cost 0.000000
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drop table t1;
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FLUSH STATUS;
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SHOW STATUS LIKE 'max_used_connections';
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Variable_name Value
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Max_used_connections 1
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SELECT * FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME LIKE 'max_used_connections';
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VARIABLE_NAME VARIABLE_VALUE
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MAX_USED_CONNECTIONS 1
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SET @save_thread_cache_size=@@thread_cache_size;
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SET GLOBAL thread_cache_size=3;
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SHOW STATUS LIKE 'max_used_connections';
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Variable_name Value
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Max_used_connections 3
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SELECT * FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME LIKE 'max_used_connections';
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VARIABLE_NAME VARIABLE_VALUE
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MAX_USED_CONNECTIONS 3
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FLUSH STATUS;
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SHOW STATUS LIKE 'max_used_connections';
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Variable_name Value
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Max_used_connections 2
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SELECT * FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME LIKE 'max_used_connections';
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VARIABLE_NAME VARIABLE_VALUE
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MAX_USED_CONNECTIONS 2
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SHOW STATUS LIKE 'max_used_connections';
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Variable_name Value
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Max_used_connections 3
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SELECT * FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME LIKE 'max_used_connections';
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VARIABLE_NAME VARIABLE_VALUE
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MAX_USED_CONNECTIONS 3
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SHOW STATUS LIKE 'max_used_connections';
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Variable_name Value
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Max_used_connections 4
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SELECT * FROM INFORMATION_SCHEMA.SESSION_STATUS WHERE VARIABLE_NAME LIKE 'max_used_connections';
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VARIABLE_NAME VARIABLE_VALUE
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MAX_USED_CONNECTIONS 4
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SET GLOBAL thread_cache_size=@save_thread_cache_size;
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show status like 'com_show_status';
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Variable_name Value
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Com_show_status 3
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show status like 'hand%write%';
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Variable_name Value
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Handler_write 5
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show status like '%tmp%';
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Variable_name Value
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Created_tmp_disk_tables 0
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Created_tmp_files 0
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Created_tmp_tables 0
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show status like 'hand%write%';
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Variable_name Value
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Handler_write 7
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show status like '%tmp%';
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Variable_name Value
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Created_tmp_disk_tables 0
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Created_tmp_files 0
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Created_tmp_tables 0
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show status like 'com_show_status';
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Variable_name Value
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Com_show_status 8
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rnd_diff tmp_table_diff
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20 8
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