7.11.2. Tuning Server Parameters

You can determine the default buffer sizes used by the mysqld server using this command:

shell> mysqld --verbose --help

This command produces a list of all mysqld options and configurable system variables. The output includes the default variable values and looks something like this:

abort-slave-event-count           0
allow-suspicious-udfs             FALSE
auto-increment-increment          1
auto-increment-offset             1
automatic-sp-privileges           TRUE
back_log                          50
basedir                           /home/jon/bin/mysql-5.5/
bind-address                      (No default value)
binlog-row-event-max-size         1024
binlog_cache_size                 32768
binlog_format                     (No default value)
bulk_insert_buffer_size           8388608
character-set-client-handshake    TRUE
character-set-filesystem          binary
character-set-server              latin1
character-sets-dir                /home/jon/bin/mysql-5.5/share/mysql/charsets/
chroot                            (No default value)
collation-server                  latin1_swedish_ci
completion-type                   0
concurrent-insert                 1
connect_timeout                   10
console                           FALSE
datadir                           .
datetime_format                   %Y-%m-%d %H:%i:%s
date_format                       %Y-%m-%d
default-character-set             latin1
default-collation                 latin1_swedish_ci
default-storage-engine            MyISAM
default-time-zone                 (No default value)
default_week_format               0
delayed_insert_limit              100
delayed_insert_timeout            300
delayed_queue_size                1000
disconnect-slave-event-count      0
div_precision_increment           4
engine-condition-pushdown         TRUE
expire_logs_days                  0
external-locking                  FALSE
flush_time                        0
ft_max_word_len                   84
ft_min_word_len                   4
ft_query_expansion_limit          20
ft_stopword_file                  (No default value)
gdb                               FALSE
general_log                       FALSE
general_log_file                  (No default value)
group_concat_max_len              1024
help                              TRUE
init-connect                      (No default value)
init-file                         (No default value)
init-slave                        (No default value)
innodb                            TRUE
innodb-adaptive-hash-index        TRUE
innodb-additional-mem-pool-size   1048576
innodb-autoextend-increment       8
innodb-autoinc-lock-mode          1
innodb-buffer-pool-size           8388608
innodb-checksums                  TRUE
innodb-commit-concurrency         0
innodb-concurrency-tickets        500
innodb-data-file-path             (No default value)
innodb-data-home-dir              (No default value)
innodb-doublewrite                TRUE
innodb-fast-shutdown              1
innodb-file-io-threads            4
innodb-file-per-table             FALSE
innodb-flush-log-at-trx-commit    1
innodb-flush-method               (No default value)
innodb-force-recovery             0
innodb-lock-wait-timeout          50
innodb-locks-unsafe-for-binlog    FALSE
innodb-log-buffer-size            1048576
innodb-log-file-size              5242880
innodb-log-files-in-group         2
innodb-log-group-home-dir         (No default value)
innodb-max-dirty-pages-pct        90
innodb-max-purge-lag              0
innodb-mirrored-log-groups        1
innodb-open-files                 300
innodb-rollback-on-timeout        FALSE
innodb-stats-on-metadata          TRUE
innodb-status-file                FALSE
innodb-support-xa                 TRUE
innodb-sync-spin-loops            20
innodb-table-locks                TRUE
innodb-thread-concurrency         8
innodb-thread-sleep-delay         10000
interactive_timeout               28800
join_buffer_size                  131072
keep_files_on_create              FALSE
key_buffer_size                   8384512
key_cache_age_threshold           300
key_cache_block_size              1024
key_cache_division_limit          100
language                          /home/jon/bin/mysql-5.5/share/mysql/english/
large-pages                       FALSE
lc-time-names                     en_US
local-infile                      TRUE
log                               (No default value)
log-bin                           (No default value)
log-bin-index                     (No default value)
log-bin-trust-function-creators   FALSE
log-isam                          myisam.log
log-output                        FILE
log-queries-not-using-indexes     FALSE
log-short-format                  FALSE
log-slave-updates                 FALSE
log-slow-admin-statements         FALSE
log-slow-slave-statements         FALSE
log-tc                            tc.log
log-tc-size                       24576
log-warnings                      1
log_slow_queries                  (No default value)
long_query_time                   10
low-priority-updates              FALSE
lower_case_table_names            0
master-retry-count                86400
max-binlog-dump-events            0
max_allowed_packet                1048576
max_binlog_cache_size             18446744073709547520
max_binlog_size                   1073741824
max_connections                   151
max_connect_errors                10
max_delayed_threads               20
max_error_count                   64
max_heap_table_size               16777216
max_join_size                     18446744073709551615
max_length_for_sort_data          1024
max_prepared_stmt_count           16382
max_relay_log_size                0
max_seeks_for_key                 18446744073709551615
max_sort_length                   1024
max_sp_recursion_depth            0
max_tmp_tables                    32
max_user_connections              0
max_write_lock_count              18446744073709551615
memlock                           FALSE
min_examined_row_limit            0
multi_range_count                 256
myisam-recover-options            OFF
myisam_block_size                 1024
myisam_data_pointer_size          6
myisam_max_sort_file_size         9223372036853727232
myisam_repair_threads             1
myisam_sort_buffer_size           8388608
myisam_stats_method               nulls_unequal
myisam_use_mmap                   FALSE
ndb-autoincrement-prefetch-sz     1
ndb-cache-check-time              0
ndb-connectstring                 (No default value)
ndb-extra-logging                 0
ndb-force-send                    TRUE
ndb-index-stat-enable             FALSE
ndb-mgmd-host                     (No default value)
ndb-nodeid                        0
ndb-optimized-node-selection      TRUE
ndb-report-thresh-binlog-epoch-slip 3
ndb-report-thresh-binlog-mem-usage 10
ndb-shm                           FALSE
ndb-use-copying-alter-table       FALSE
ndb-use-exact-count               TRUE
ndb-use-transactions              TRUE
ndb_force_send                    TRUE
ndb_use_exact_count               TRUE
ndb_use_transactions              TRUE
net_buffer_length                 16384
net_read_timeout                  30
net_retry_count                   10
net_write_timeout                 60
new                               FALSE
old                               FALSE
old-alter-table                   FALSE
old-passwords                     FALSE
old-style-user-limits             FALSE
open_files_limit                  1024
optimizer_prune_level             1
optimizer_search_depth            62
pid-file                          /home/jon/bin/mysql-5.5/var/tonfisk.pid
plugin-load                       (No default value)
plugin_dir                        /home/jon/bin/mysql-5.5/lib/mysql/plugin
port                              3306
port-open-timeout                 0
preload_buffer_size               32768
profiling_history_size            15
query_alloc_block_size            8192
query_cache_limit                 1048576
query_cache_min_res_unit          4096
query_cache_size                  0
query_cache_type                  1
query_cache_wlock_invalidate      FALSE
query_prealloc_size               8192
range_alloc_block_size            4096
read_buffer_size                  131072
read_only                         FALSE
read_rnd_buffer_size              262144
relay-log                         (No default value)
relay-log-index                   (No default value)
relay-log-info-file               relay-log.info
relay_log_purge                   TRUE
relay_log_space_limit             0
replicate-same-server-id          FALSE
report-host                       (No default value)
report-password                   (No default value)
report-port                       3306
report-user                       (No default value)
rpl-recovery-rank                 0
safe-user-create                  FALSE
secure-auth                       FALSE
secure-file-priv                  (No default value)
server-id                         0
show-slave-auth-info              FALSE
skip-grant-tables                 FALSE
skip-slave-start                  FALSE
slave-exec-mode                   STRICT
slave-load-tmpdir                 /tmp
slave_compressed_protocol         FALSE
slave_net_timeout                 3600
slave_transaction_retries         10
slow-query-log                    FALSE
slow_launch_time                  2
slow_query_log_file               (No default value)
socket                            /tmp/mysql.sock
sort_buffer_size                  2097144
sporadic-binlog-dump-fail         FALSE
sql-mode                          OFF
symbolic-links                    TRUE
sync-binlog                       0
sync-frm                          TRUE
sysdate-is-now                    FALSE
table_definition_cache            256
table_open_cache                  400
tc-heuristic-recover              (No default value)
temp-pool                         TRUE
thread_cache_size                 0
thread_concurrency                10
thread_stack                      262144
timed_mutexes                     FALSE
time_format                       %H:%i:%s
tmpdir                            (No default value)
tmp_table_size                    16777216
transaction_alloc_block_size      8192
transaction_prealloc_size         4096
updatable_views_with_limit        1
verbose                           TRUE
wait_timeout                      28800

For a mysqld server that is currently running, you can see the current values of its system variables by connecting to it and issuing this statement:


You can also see some statistical and status indicators for a running server by issuing this statement:


System variable and status information also can be obtained using mysqladmin:

shell> mysqladmin variables
shell> mysqladmin extended-status

For a full description of all system and status variables, see Section 5.1.4, “Server System Variables”, and Section 5.1.6, “Server Status Variables”.

MySQL uses algorithms that are very scalable, so you can usually run with very little memory. However, normally you get better performance by giving MySQL more memory.

When tuning a MySQL server, the two most important variables to configure are key_buffer_size and table_open_cache. You should first feel confident that you have these set appropriately before trying to change any other variables.

The following examples indicate some typical variable values for different runtime configurations.

  • If you have at least 256MB of memory and many tables and want maximum performance with a moderate number of clients, use something like this:

    shell> mysqld_safe --key_buffer_size=64M --table_open_cache=256 \
               --sort_buffer_size=4M --read_buffer_size=1M &
  • If you have only 128MB of memory and only a few tables, but you still do a lot of sorting, you can use something like this:

    shell> mysqld_safe --key_buffer_size=16M --sort_buffer_size=1M

    If there are very many simultaneous connections, swapping problems may occur unless mysqld has been configured to use very little memory for each connection. mysqld performs better if you have enough memory for all connections.

  • With little memory and lots of connections, use something like this:

    shell> mysqld_safe --key_buffer_size=512K --sort_buffer_size=100K \
               --read_buffer_size=100K &

    Or even this:

    shell> mysqld_safe --key_buffer_size=512K --sort_buffer_size=16K \
               --table_open_cache=32 --read_buffer_size=8K \
               --net_buffer_length=1K &

If you are performing GROUP BY or ORDER BY operations on tables that are much larger than your available memory, increase the value of read_rnd_buffer_size to speed up the reading of rows following sorting operations.

You can make use of the example option files included with your MySQL distribution; see Section, “Preconfigured Option Files”.

If you specify an option on the command line for mysqld or mysqld_safe, it remains in effect only for that invocation of the server. To use the option every time the server runs, put it in an option file.

To see the effects of a parameter change, do something like this:

shell> mysqld --key_buffer_size=32M --verbose --help

The variable values are listed near the end of the output. Make sure that the --verbose and --help options are last. Otherwise, the effect of any options listed after them on the command line are not reflected in the output.

For information on tuning the InnoDB storage engine, see Section, “InnoDB Performance Tuning Tips”.

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