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7.5.2 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:
back_log 50
binlog_cache_size 32768
bulk_insert_buffer_size 8388608
connect_timeout 5
date_format (No default value)
datetime_format (No default value)
default_week_format 0
delayed_insert_limit 100
delayed_insert_timeout 300
delayed_queue_size 1000
expire_logs_days 0
flush_time 1800
ft_max_word_len 84
ft_min_word_len 4
ft_query_expansion_limit 20
ft_stopword_file (No default value)
group_concat_max_len 1024
innodb_additional_mem_pool_size 1048576
innodb_autoextend_increment 8
innodb_buffer_pool_awe_mem_mb 0
innodb_buffer_pool_size 8388608
innodb_concurrency_tickets 500
innodb_file_io_threads 4
innodb_force_recovery 0
innodb_lock_wait_timeout 50
innodb_log_buffer_size 1048576
innodb_log_file_size 5242880
innodb_log_files_in_group 2
innodb_mirrored_log_groups 1
innodb_open_files 300
innodb_sync_spin_loops 20
innodb_thread_concurrency 8
innodb_thread_sleep_delay 10000
interactive_timeout 28800
join_buffer_size 131072
key_buffer_size 8388600
key_cache_age_threshold 300
key_cache_block_size 1024
key_cache_division_limit 100
long_query_time 10
lower_case_table_names 1
max_allowed_packet 1048576
max_binlog_cache_size 4294967295
max_binlog_size 1073741824
max_connect_errors 10
max_connections 100
max_delayed_threads 20
max_error_count 64
max_heap_table_size 16777216
max_join_size 4294967295
max_length_for_sort_data 1024
max_relay_log_size 0
max_seeks_for_key 4294967295
max_sort_length 1024
max_tmp_tables 32
max_user_connections 0
max_write_lock_count 4294967295
multi_range_count 256
myisam_block_size 1024
myisam_data_pointer_size 6
myisam_max_extra_sort_file_size 2147483648
myisam_max_sort_file_size 2147483647
myisam_repair_threads 1
myisam_sort_buffer_size 8388608
net_buffer_length 16384
net_read_timeout 30
net_retry_count 10
net_write_timeout 60
open_files_limit 0
optimizer_prune_level 1
optimizer_search_depth 62
preload_buffer_size 32768
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 2048
read_buffer_size 131072
read_only FALSE
read_rnd_buffer_size 262144
div_precision_increment 4
record_buffer 131072
relay_log_purge TRUE
relay_log_space_limit 0
slave_compressed_protocol FALSE
slave_net_timeout 3600
slave_transaction_retries 10
slow_launch_time 2
sort_buffer_size 2097144
sync-binlog 0
sync-frm TRUE
sync-replication 0
sync-replication-slave-id 0
sync-replication-timeout 10
table_cache 64
thread_cache_size 0
thread_concurrency 10
thread_stack 196608
time_format (No default value)
tmp_table_size 33554432
transaction_alloc_block_size 8192
transaction_prealloc_size 4096
updatable_views_with_limit 1
wait_timeout 28800
If there is a `mysqld' server currently running, you can see the
current values of its system variables by connecting to it and issuing
this statement:
mysql> SHOW VARIABLES;
You can also see some statistical and status indicators for a running
server by issuing this statement:
mysql> SHOW STATUS;
System variable and status information also can be obtained using
`mysqladmin':
shell> mysqladmin variables
shell> mysqladmin extended-status
For a full description for all system and status variables, see
server-system-variables, and 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_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, you should
use something like this:
shell> mysqld_safe --key_buffer_size=64M --table_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_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, you should increase
the value of `read_rnd_buffer_size' to speed up the reading of rows
following sorting operations.
When you have installed MySQL, the `support-files' directory contains
some different `my.cnf' sample files: `my-huge.cnf', `my-large.cnf',
`my-medium.cnf', and `my-small.cnf'. You can use these as a basis for
optimizing your system. (On Windows, look in the MySQL installation
directory.)
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
innodb-tuning.
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