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:
help TRUE
abort-slave-event-count 0
allow-suspicious-udfs FALSE
auto-increment-increment 1
auto-increment-offset 1
automatic-sp-privileges TRUE
basedir /home/jon/bin/mysql/
bdb FALSE
bind-address (No default value)
character-set-client-handshake TRUE
character-set-server latin1
character-sets-dir /home/jon/bin/mysql/share/mysql/charsets/
chroot (No default value)
collation-server latin1_swedish_ci
completion-type 0
concurrent-insert 1
console FALSE
datadir /home/jon/bin/mysql/var/
default-character-set latin1
default-collation latin1_swedish_ci
default-time-zone (No default value)
disconnect-slave-event-count 0
enable-locking FALSE
enable-pstack FALSE
engine-condition-pushdown FALSE
external-locking FALSE
gdb FALSE
large-pages FALSE
init-connect (No default value)
init-file (No default value)
init-slave (No default value)
innodb TRUE
innodb_checksums TRUE
innodb_data_home_dir (No default value)
innodb_doublewrite TRUE
innodb_fast_shutdown 1
innodb_file_per_table FALSE
innodb_flush_log_at_trx_commit 1
innodb_flush_method (No default value)
innodb_locks_unsafe_for_binlog FALSE
innodb_log_arch_dir (No default value)
innodb_log_group_home_dir (No default value)
innodb_max_dirty_pages_pct 90
innodb_max_purge_lag 0
innodb_status_file FALSE
innodb_table_locks TRUE
innodb_support_xa TRUE
isam FALSE
language /home/jon/bin/mysql/share/mysql/english
local-infile TRUE
log /home/jon/bin/mysql/var/master1.log
log-bin /home/jon/bin/mysql/var/master1
log-bin-index (No default value)
log-bin-trust-routine-creators FALSE
log-error /home/jon/bin/mysql/var/master1.err
log-isam myisam.log
log-queries-not-using-indexes FALSE
log-short-format FALSE
log-slave-updates FALSE
log-slow-admin-statements FALSE
log-slow-queries (No default value)
log-tc tc.log
log-tc-size 24576
log-update (No default value)
log-warnings 1
low-priority-updates FALSE
master-connect-retry 60
master-host (No default value)
master-info-file master.info
master-password (No default value)
master-port 3306
master-retry-count 86400
master-ssl FALSE
master-ssl-ca (No default value)
master-ssl-capath (No default value)
master-ssl-cert (No default value)
master-ssl-cipher (No default value)
master-ssl-key (No default value)
master-user test
max-binlog-dump-events 0
memlock FALSE
myisam-recover OFF
ndbcluster FALSE
ndb-connectstring (No default value)
ndb-mgmd-host (No default value)
ndb-nodeid 0
ndb-autoincrement-prefetch-sz 32
ndb-distibution KEYHASH
ndb-force-send TRUE
ndb_force_send TRUE
ndb-use-exact-count TRUE
ndb_use_exact_count TRUE
ndb-shm FALSE
ndb-optimized-node-selection TRUE
ndb-cache-check-time 0
ndb-index-stat-enable TRUE
ndb-index-stat-cache-entries 32
ndb-index-stat-update-freq 20
new FALSE
old-alter-table FALSE
old-passwords FALSE
old-style-user-limits FALSE
pid-file /home/jon/bin/mysql/var/hostname.pid1
port 3306
relay-log (No default value)
relay-log-index (No default value)
relay-log-info-file relay-log.info
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
server-id 1
show-slave-auth-info FALSE
skip-grant-tables FALSE
skip-slave-start FALSE
slave-load-tmpdir /tmp/
socket /tmp/mysql.sock
sporadic-binlog-dump-fail FALSE
sql-mode OFF
symbolic-links TRUE
tc-heuristic-recover (No default value)
temp-pool TRUE
timed_mutexes FALSE
tmpdir (No default value)
use-symbolic-links TRUE
verbose TRUE
warnings 1
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 0
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 20
innodb_commit_concurrency 0
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 0
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
myisam_stats_method nulls_unequal
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_open_cache 64
table_lock_wait_timeout 50
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
Section 5.2.2, “Server System Variables”, and
Section 5.2.4, “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,
you should 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, 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 Section 14.2.11, “InnoDB Performance Tuning Tips”.
