MySQL 8.4 Reference Manual Including MySQL NDB Cluster 8.4
A mutex is a synchronization mechanism used in the code to enforce that only one thread at a given time can have access to a common resource. When two or more threads executing in the server need to access the same resource, the threads compete against each other. The first thread to obtain a lock on the mutex causes the other threads to wait until the lock is released.
For InnoDB mutexes that are instrumented, mutex
waits can be monitored using
Performance Schema. Wait
event data collected in Performance Schema tables can help
identify mutexes with the most waits or the greatest total wait
time, for example.
The following example demonstrates how to enable
InnoDB mutex wait instruments, how to enable
associated consumers, and how to query wait event data.
To view available InnoDB mutex wait
instruments, query the Performance Schema
setup_instruments table. All
InnoDB mutex wait instruments are disabled
by default.
mysql>SELECT *FROM performance_schema.setup_instrumentsWHERE NAME LIKE '%wait/synch/mutex/innodb%';+---------------------------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +---------------------------------------------------------+---------+-------+ | wait/synch/mutex/innodb/commit_cond_mutex | NO | NO | | wait/synch/mutex/innodb/innobase_share_mutex | NO | NO | | wait/synch/mutex/innodb/autoinc_mutex | NO | NO | | wait/synch/mutex/innodb/autoinc_persisted_mutex | NO | NO | | wait/synch/mutex/innodb/buf_pool_flush_state_mutex | NO | NO | | wait/synch/mutex/innodb/buf_pool_LRU_list_mutex | NO | NO | | wait/synch/mutex/innodb/buf_pool_free_list_mutex | NO | NO | | wait/synch/mutex/innodb/buf_pool_zip_free_mutex | NO | NO | | wait/synch/mutex/innodb/buf_pool_zip_hash_mutex | NO | NO | | wait/synch/mutex/innodb/buf_pool_zip_mutex | NO | NO | | wait/synch/mutex/innodb/cache_last_read_mutex | NO | NO | | wait/synch/mutex/innodb/dict_foreign_err_mutex | NO | NO | | wait/synch/mutex/innodb/dict_persist_dirty_tables_mutex | NO | NO | | wait/synch/mutex/innodb/dict_sys_mutex | NO | NO | | wait/synch/mutex/innodb/recalc_pool_mutex | NO | NO | | wait/synch/mutex/innodb/fil_system_mutex | NO | NO | | wait/synch/mutex/innodb/flush_list_mutex | NO | NO | | wait/synch/mutex/innodb/fts_bg_threads_mutex | NO | NO | | wait/synch/mutex/innodb/fts_delete_mutex | NO | NO | | wait/synch/mutex/innodb/fts_optimize_mutex | NO | NO | | wait/synch/mutex/innodb/fts_doc_id_mutex | NO | NO | | wait/synch/mutex/innodb/log_flush_order_mutex | NO | NO | | wait/synch/mutex/innodb/hash_table_mutex | NO | NO | | wait/synch/mutex/innodb/ibuf_bitmap_mutex | NO | NO | | wait/synch/mutex/innodb/ibuf_mutex | NO | NO | | wait/synch/mutex/innodb/ibuf_pessimistic_insert_mutex | NO | NO | | wait/synch/mutex/innodb/log_sys_mutex | NO | NO | | wait/synch/mutex/innodb/log_sys_write_mutex | NO | NO | | wait/synch/mutex/innodb/mutex_list_mutex | NO | NO | | wait/synch/mutex/innodb/page_zip_stat_per_index_mutex | NO | NO | | wait/synch/mutex/innodb/purge_sys_pq_mutex | NO | NO | | wait/synch/mutex/innodb/recv_sys_mutex | NO | NO | | wait/synch/mutex/innodb/recv_writer_mutex | NO | NO | | wait/synch/mutex/innodb/redo_rseg_mutex | NO | NO | | wait/synch/mutex/innodb/noredo_rseg_mutex | NO | NO | | wait/synch/mutex/innodb/rw_lock_list_mutex | NO | NO | | wait/synch/mutex/innodb/rw_lock_mutex | NO | NO | | wait/synch/mutex/innodb/srv_dict_tmpfile_mutex | NO | NO | | wait/synch/mutex/innodb/srv_innodb_monitor_mutex | NO | NO | | wait/synch/mutex/innodb/srv_misc_tmpfile_mutex | NO | NO | | wait/synch/mutex/innodb/srv_monitor_file_mutex | NO | NO | | wait/synch/mutex/innodb/buf_dblwr_mutex | NO | NO | | wait/synch/mutex/innodb/trx_undo_mutex | NO | NO | | wait/synch/mutex/innodb/trx_pool_mutex | NO | NO | | wait/synch/mutex/innodb/trx_pool_manager_mutex | NO | NO | | wait/synch/mutex/innodb/srv_sys_mutex | NO | NO | | wait/synch/mutex/innodb/lock_mutex | NO | NO | | wait/synch/mutex/innodb/lock_wait_mutex | NO | NO | | wait/synch/mutex/innodb/trx_mutex | NO | NO | | wait/synch/mutex/innodb/srv_threads_mutex | NO | NO | | wait/synch/mutex/innodb/rtr_active_mutex | NO | NO | | wait/synch/mutex/innodb/rtr_match_mutex | NO | NO | | wait/synch/mutex/innodb/rtr_path_mutex | NO | NO | | wait/synch/mutex/innodb/rtr_ssn_mutex | NO | NO | | wait/synch/mutex/innodb/trx_sys_mutex | NO | NO | | wait/synch/mutex/innodb/zip_pad_mutex | NO | NO | | wait/synch/mutex/innodb/master_key_id_mutex | NO | NO | +---------------------------------------------------------+---------+-------+
Some InnoDB mutex instances are created at
server startup and are only instrumented if the associated
instrument is also enabled at server startup. To ensure that
all InnoDB mutex instances are instrumented
and enabled, add the following
performance-schema-instrument rule to your
MySQL configuration file:
performance-schema-instrument='wait/synch/mutex/innodb/%=ON'
If you do not require wait event data for all
InnoDB mutexes, you can disable specific
instruments by adding additional
performance-schema-instrument rules to your
MySQL configuration file. For example, to disable
InnoDB mutex wait event instruments related
to full-text search, add the following rule:
performance-schema-instrument='wait/synch/mutex/innodb/fts%=OFF'
Rules with a longer prefix such as
wait/synch/mutex/innodb/fts% take
precedence over rules with shorter prefixes such as
wait/synch/mutex/innodb/%.
After adding the
performance-schema-instrument rules to your
configuration file, restart the server. All the
InnoDB mutexes except for those related to
full text search are enabled. To verify, query the
setup_instruments table. The
ENABLED and TIMED
columns should be set to YES for the
instruments that you enabled.
mysql>SELECT *FROM performance_schema.setup_instrumentsWHERE NAME LIKE '%wait/synch/mutex/innodb%';+-------------------------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +-------------------------------------------------------+---------+-------+ | wait/synch/mutex/innodb/commit_cond_mutex | YES | YES | | wait/synch/mutex/innodb/innobase_share_mutex | YES | YES | | wait/synch/mutex/innodb/autoinc_mutex | YES | YES | ... | wait/synch/mutex/innodb/master_key_id_mutex | YES | YES | +-------------------------------------------------------+---------+-------+ 49 rows in set (0.00 sec)
Enable wait event consumers by updating the
setup_consumers table. Wait event
consumers are disabled by default.
mysql>UPDATE performance_schema.setup_consumersSET enabled = 'YES'WHERE name like 'events_waits%';Query OK, 3 rows affected (0.00 sec) Rows matched: 3 Changed: 3 Warnings: 0
You can verify that wait event consumers are enabled by
querying the setup_consumers
table. The events_waits_current,
events_waits_history, and
events_waits_history_long
consumers should be enabled.
mysql> SELECT * FROM performance_schema.setup_consumers;
+----------------------------------+---------+
| NAME | ENABLED |
+----------------------------------+---------+
| events_stages_current | NO |
| events_stages_history | NO |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | YES |
| events_statements_history_long | NO |
| events_transactions_current | YES |
| events_transactions_history | YES |
| events_transactions_history_long | NO |
| events_waits_current | YES |
| events_waits_history | YES |
| events_waits_history_long | YES |
| global_instrumentation | YES |
| thread_instrumentation | YES |
| statements_digest | YES |
+----------------------------------+---------+
15 rows in set (0.00 sec)
Once instruments and consumers are enabled, run the workload that you want to monitor. In this example, the mysqlslap load emulation client is used to simulate a workload.
$>./mysqlslap --auto-generate-sql --concurrency=100 --iterations=10--number-of-queries=1000 --number-char-cols=6 --number-int-cols=6;
Query the wait event data. In this example, wait event data is
queried from the
events_waits_summary_global_by_event_name
table which aggregates data found in the
events_waits_current,
events_waits_history, and
events_waits_history_long tables.
Data is summarized by event name
(EVENT_NAME), which is the name of the
instrument that produced the event. Summarized data includes:
COUNT_STAR
The number of summarized wait events.
SUM_TIMER_WAIT
The total wait time of the summarized timed wait events.
MIN_TIMER_WAIT
The minimum wait time of the summarized timed wait events.
AVG_TIMER_WAIT
The average wait time of the summarized timed wait events.
MAX_TIMER_WAIT
The maximum wait time of the summarized timed wait events.
The following query returns the instrument name
(EVENT_NAME), the number of wait events
(COUNT_STAR), and the total wait time for
the events for that instrument
(SUM_TIMER_WAIT). Because waits are timed
in picoseconds (trillionths of a second) by default, wait
times are divided by 1000000000 to show wait times in
milliseconds. Data is presented in descending order, by the
number of summarized wait events
(COUNT_STAR). You can adjust the
ORDER BY clause to order the data by total
wait time.
mysql>SELECT EVENT_NAME, COUNT_STAR, SUM_TIMER_WAIT/1000000000 SUM_TIMER_WAIT_MSFROM performance_schema.events_waits_summary_global_by_event_nameWHERE SUM_TIMER_WAIT > 0 AND EVENT_NAME LIKE 'wait/synch/mutex/innodb/%'ORDER BY COUNT_STAR DESC;+---------------------------------------------------------+------------+-------------------+ | EVENT_NAME | COUNT_STAR | SUM_TIMER_WAIT_MS | +---------------------------------------------------------+------------+-------------------+ | wait/synch/mutex/innodb/trx_mutex | 201111 | 23.4719 | | wait/synch/mutex/innodb/fil_system_mutex | 62244 | 9.6426 | | wait/synch/mutex/innodb/redo_rseg_mutex | 48238 | 3.1135 | | wait/synch/mutex/innodb/log_sys_mutex | 46113 | 2.0434 | | wait/synch/mutex/innodb/trx_sys_mutex | 35134 | 1068.1588 | | wait/synch/mutex/innodb/lock_mutex | 34872 | 1039.2589 | | wait/synch/mutex/innodb/log_sys_write_mutex | 17805 | 1526.0490 | | wait/synch/mutex/innodb/dict_sys_mutex | 14912 | 1606.7348 | | wait/synch/mutex/innodb/trx_undo_mutex | 10634 | 1.1424 | | wait/synch/mutex/innodb/rw_lock_list_mutex | 8538 | 0.1960 | | wait/synch/mutex/innodb/buf_pool_free_list_mutex | 5961 | 0.6473 | | wait/synch/mutex/innodb/trx_pool_mutex | 4885 | 8821.7496 | | wait/synch/mutex/innodb/buf_pool_LRU_list_mutex | 4364 | 0.2077 | | wait/synch/mutex/innodb/innobase_share_mutex | 3212 | 0.2650 | | wait/synch/mutex/innodb/flush_list_mutex | 3178 | 0.2349 | | wait/synch/mutex/innodb/trx_pool_manager_mutex | 2495 | 0.1310 | | wait/synch/mutex/innodb/buf_pool_flush_state_mutex | 1318 | 0.2161 | | wait/synch/mutex/innodb/log_flush_order_mutex | 1250 | 0.0893 | | wait/synch/mutex/innodb/buf_dblwr_mutex | 951 | 0.0918 | | wait/synch/mutex/innodb/recalc_pool_mutex | 670 | 0.0942 | | wait/synch/mutex/innodb/dict_persist_dirty_tables_mutex | 345 | 0.0414 | | wait/synch/mutex/innodb/lock_wait_mutex | 303 | 0.1565 | | wait/synch/mutex/innodb/autoinc_mutex | 196 | 0.0213 | | wait/synch/mutex/innodb/autoinc_persisted_mutex | 196 | 0.0175 | | wait/synch/mutex/innodb/purge_sys_pq_mutex | 117 | 0.0308 | | wait/synch/mutex/innodb/srv_sys_mutex | 94 | 0.0077 | | wait/synch/mutex/innodb/ibuf_mutex | 22 | 0.0086 | | wait/synch/mutex/innodb/recv_sys_mutex | 12 | 0.0008 | | wait/synch/mutex/innodb/srv_innodb_monitor_mutex | 4 | 0.0009 | | wait/synch/mutex/innodb/recv_writer_mutex | 1 | 0.0005 | +---------------------------------------------------------+------------+-------------------+
The preceding result set includes wait event data produced
during the startup process. To exclude this data, you can
truncate the
events_waits_summary_global_by_event_name
table immediately after startup and before running your
workload. However, the truncate operation itself may produce
a negligible amount wait event data.
mysql> TRUNCATE performance_schema.events_waits_summary_global_by_event_name;