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MySQL 5.5 and 5.6 default variable values differences

02.22.2013
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 As the part of analyzing surprising MySQL 5.5 vs 5.6 performance results I’ve been looking at changes to default variable values. To do that I’ve loaded the values from MySQL 5.5.30 and 5.6.10 to the different tables and ran the query:

mysql [localhost] {msandbox} (test) > select var55.variable_name,left(var55.variable_value,40) value55, left(var56.variable_value,40) var56  from var55 left join var56 on var55.variable_name=var56.variable_name where  var55.variable_value!=var56.variable_value;
+---------------------------------------------------+------------------------------------------+------------------------------------------+
| variable_name                                     | value55                                  | var56                                    |
+---------------------------------------------------+------------------------------------------+------------------------------------------+
| PERFORMANCE_SCHEMA                                | OFF                                      | ON                                       |
| PID_FILE                                          | /mnt/data/sandboxes/msb_5_5_30/data/mysq | /mnt/data/sandboxes/msb_5_6_10/data/mysq |
| CHARACTER_SETS_DIR                                | /mnt/nfs/dist/mysql-5.5.30-linux2.6-x86_ | /mnt/nfs/dist/mysql-5.6.10-linux-glibc2. |
| PERFORMANCE_SCHEMA_MAX_COND_INSTANCES             | 1000                                     | 836                                      |
| PERFORMANCE_SCHEMA_MAX_MUTEX_INSTANCES            | 1000000                                  | 3282                                     |
| OLD_PASSWORDS                                     | OFF                                      | 0                                        |
| INNODB_STATS_ON_METADATA                          | ON                                       | OFF                                      |
| PERFORMANCE_SCHEMA_EVENTS_WAITS_HISTORY_SIZE      | 10                                       | 5                                        |
| PERFORMANCE_SCHEMA_EVENTS_WAITS_HISTORY_LONG_SIZE | 10000                                    | 100                                      |
| PERFORMANCE_SCHEMA_MAX_RWLOCK_INSTANCES           | 1000000                                  | 1724                                     |
| PERFORMANCE_SCHEMA_MAX_TABLE_HANDLES              | 100000                                   | 2223                                     |
| INNODB_LOG_FILE_SIZE                              | 5242880                                  | 50331648                                 |
| BASEDIR                                           | /mnt/nfs/dist/5.5.30                     | /mnt/nfs/dist/5.6.10                     |
| BACK_LOG                                          | 50                                       | 80                                       |
| OPEN_FILES_LIMIT                                  | 1024                                     | 5000                                     |
| INNODB_AUTOEXTEND_INCREMENT                       | 8                                        | 64                                       |
| MAX_CONNECT_ERRORS                                | 10                                       | 100                                      |
| SORT_BUFFER_SIZE                                  | 2097152                                  | 262144                                   |
| LC_MESSAGES_DIR                                   | /mnt/nfs/dist/mysql-5.5.30-linux2.6-x86_ | /mnt/nfs/dist/mysql-5.6.10-linux-glibc2. |
| MAX_ALLOWED_PACKET                                | 1048576                                  | 4194304                                  |
| JOIN_BUFFER_SIZE                                  | 131072                                   | 262144                                   |
| TMPDIR                                            | /mnt/data/sandboxes/msb_5_5_30/tmp       | /mnt/data/sandboxes/msb_5_6_10/tmp       |
| TABLE_OPEN_CACHE                                  | 400                                      | 2000                                     |
| INNODB_VERSION                                    | 5.5.30                                   | 1.2.10                                   |
| INNODB_BUFFER_POOL_INSTANCES                      | 1                                        | 8                                        |
| QUERY_CACHE_SIZE                                  | 0                                        | 1048576                                  |
| SLOW_QUERY_LOG_FILE                               | /mnt/data/sandboxes/msb_5_5_30/data/dpe0 | /mnt/data/sandboxes/msb_5_6_10/data/dpe0 |
| TABLE_DEFINITION_CACHE                            | 400                                      | 1400                                     |
| PORT                                              | 5530                                     | 5610                                     |
| QUERY_CACHE_TYPE                                  | ON                                       | OFF                                      |
| REPORT_PORT                                       | 5530                                     | 5610                                     |
| PERFORMANCE_SCHEMA_MAX_FILE_INSTANCES             | 10000                                    | 1556                                     |
| SQL_MODE                                          |                                          | NO_ENGINE_SUBSTITUTION                   |
| INNODB_OLD_BLOCKS_TIME                            | 0                                        | 1000                                     |
| LOG_ERROR                                         | /mnt/data/sandboxes/msb_5_5_30/data/msan | /mnt/data/sandboxes/msb_5_6_10/data/msan |
| VERSION_COMPILE_OS                                | linux2.6                                 | linux-glibc2.5                           |
| THREAD_CACHE_SIZE                                 | 0                                        | 9                                        |
| PLUGIN_DIR                                        | /mnt/nfs/dist/5.5.30/lib/plugin/         | /mnt/nfs/dist/5.6.10/lib/plugin/         |
| SYNC_RELAY_LOG                                    | 0                                        | 10000                                    |
| GENERAL_LOG_FILE                                  | /mnt/data/sandboxes/msb_5_5_30/data/dpe0 | /mnt/data/sandboxes/msb_5_6_10/data/dpe0 |
| PERFORMANCE_SCHEMA_MAX_TABLE_INSTANCES            | 50000                                    | 445                                      |
| SYNC_RELAY_LOG_INFO                               | 0                                        | 10000                                    |
| SLAVE_LOAD_TMPDIR                                 | /mnt/data/sandboxes/msb_5_5_30/tmp       | /mnt/data/sandboxes/msb_5_6_10/tmp       |
| SECURE_AUTH                                       | OFF                                      | ON                                       |
| VERSION                                           | 5.5.30                                   | 5.6.10                                   |
| INNODB_CONCURRENCY_TICKETS                        | 500                                      | 5000                                     |
| INNODB_PURGE_THREADS                              | 0                                        | 1                                        |
| INNODB_OPEN_FILES                                 | 300                                      | 2000                                     |
| INNODB_DATA_FILE_PATH                             | ibdata1:10M:autoextend                   | ibdata1:12M:autoextend                   |
| INNODB_PURGE_BATCH_SIZE                           | 20                                       | 300                                      |
| PERFORMANCE_SCHEMA_MAX_THREAD_INSTANCES           | 1000                                     | 224                                      |
| SOCKET                                            | /tmp/mysql_sandbox5530.sock              | /tmp/mysql_sandbox5610.sock              |
| INNODB_FILE_PER_TABLE                             | OFF                                      | ON                                       |
| SYNC_MASTER_INFO                                  | 0                                        | 10000                                    |
| DATADIR                                           | /mnt/data/sandboxes/msb_5_5_30/data/     | /mnt/data/sandboxes/msb_5_6_10/data/     |
| OPTIMIZER_SWITCH                                  | index_merge=on,index_merge_union=on,inde | index_merge=on,index_merge_union=on,inde |
+---------------------------------------------------+------------------------------------------+------------------------------------------+
56 rows in set (0.05 sec)

Lets go over to see what are the most important changes one needs to consider and their possible impact:

performance_schema is ON by default in MySQL 5.6 but you can see many options can be scaled down compared to MySQL 5.5 default values. Such as performance_schema auto scales to count up to 445 tables and 224 threads in this case, lower than 5.5 values. Though it makes sense as max_connections is just 150 and there are less than 200 tables in this system.

innodb_stats_on_metadata is disabled by default in MySQL 5.6 Welcome to much faster information_schema queries!

innodb_log_file_size – default has been increased from 5MB to approximately 50MB which is a good change, though I think default could have been made even larger. Write intensive workload will do a lot better on MySQL 5.6 with default configuration

back_log Minor increase 50 to 80 does not make much difference. Systems with high number of connections/sec will still need to increase it much further.

open_files_limit is 5000 by default now vs 1024.

innodb_auto_extend_increment is now 64MB instead of 8MB which should help to reduce fragmentation and make file growth more rare event.

max_connect_errors was raised from 10 to 100 which is good change to reduce the potential of blocked host errors though I think one could go with even higher default value.

sort_buffer_size was decreased to 256K from 2M. This change should help many small sorts for which allocation of 2M for sort buffer was very expensive. It can negatively impact some large sorts though shifting to sort merge much sooner.

max_allowed_packet is 4MB instead of 1MB now allowing MySQL to handle larger queries. Makes sense as amount of memory available is much larger these days.

join_buffer_size have been increased to 256K from 128K. This probably done to have more consistency among variables values. I do not expect large impact here.

table_open_cache is increased from 400 to 2000 by default. Good change making the default practical on larger set of installations

innodb_buffer_pool_instances is now 8 instead of 1 optimizing for higher concurrency workloads. Makes sense as servers have a lot more cores available these days.

query_cache_type and query_cache_size. The behavior is “no cache” by default still but it is achieved differently now. The query_cache_type is now off by default with default size of 1MB while in MySQL 5.5 and before it was “ON” by default with query cache size of 0 which makes it disabled. I wish query_cache_size though would be larger by default as value of 1M is too small to be practical if someone tries to enable it.

sql_mode has NO_ENGINE_SUBSTITUTION value by default which is good change as trying to create Innodb table but getting MyISAM because Innodb was disabled for some reason was very error prone gotcha. Note this is as far as MySQL 5.6 goes - STRICT_MODE and other safer behaviors are not enabled by default.

innodb_old_blocks_time now set to 1000 making Innodb Buffer Pool Size scan resistant by default. Very welcome change !

thread_cache_size is enabled by default, though I wonder why default value is 9. In any case very welcome change to help workloads with many connects/disconnects

sync_relay_log_info and sync_master_info have now default of 10000 instead of 0 which meant “never”. 10000 is really almost as good as never though it is designed to provide some level of guaranty independently on file system flush policy. This probably will not impact most of workloads.

secure_auth now is ON by default requiring newer password handshake,essentially blocking old insecure one. Good.

innodb_concurrency_tickets has been increased from 500 to 5000. If you’re using innodb_thread_concurrency this will reduce overhead associated with grabbing and releasing innodb_thread_concurrency slot but will increase potential starvation of queued threads especially for IO bound workloads. Most users will not be affected though as innodb_thread_concurrency is 0 by default so this queuing feature is disabled.

innodb_purge_threads is now 1 by default using dedicated background purge thread. Good change for most workloads.

innodb_open_files was increased to 2000 from 300. Good change considering open_files_limit was also raised. Unlikely to cause significant gains unless opening and closing files is expensive operation (such as using MySQL on NFS file system).

innodb_data_file_path got a small change with starting ibdata1 size raised from 10M to 12M. I’m not sure what is the purpose of this change but it is unlikely to have any practical meaning for users. Considering the default innodb_auto_extend_increment is 64 starting with 64M might have made more sense.

innodb_purge_patch_size have been increased from 20 to 300 which I guess is one of the component of purging fine tuning in MySQL 5.6

innodb_file_per_table is now ON by default. This is very big change and is good one. We have been running innodb_file_per_table=1 for most of workloads for years now. The exceptions have been when you have large number of tables or if you do many create/drop of innodb tables.

optimizer_switch is the catch all variable for a lot of optimizer options. I wonder why was not it implemented as number of different variables which would make more sense in my opinion. MySQL 5.6 adds a lot more optimizer switches which you can play with:

mysql [localhost] {msandbox} (test) > select * from var55 where variable_name='OPTIMIZER_SWITCH' \G
*************************** 1. row ***************************
 VARIABLE_NAME: OPTIMIZER_SWITCH
VARIABLE_VALUE: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on
1 row in set (0.00 sec)

mysql [localhost] {msandbox} (test) > select * from var56 where variable_name='OPTIMIZER_SWITCH' \G
*************************** 1. row ***************************
 VARIABLE_NAME: OPTIMIZER_SWITCH
VARIABLE_VALUE: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=on,mrr=on,mrr_cost_based=on,block_nested_loop=on,batched_key_access=off,materialization=on,semijoin=on,loosescan=on,firstmatch=on,subquery_materialization_cost_based=on,use_index_extensions=on
1 row in set (0.00 sec)



Published at DZone with permission of Peter Zaitsev, author and DZone MVB. (source)

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