我在 Web 服务器上有许多带有会话表的网站，这些网站被 Joomla CMS 和 Symfony 框架系统使用。当 slow_query_log=0.6 时，会话表的更新查询会定期出现在慢速日志中。
Joomla 会话表定义是
CREATE TABLE IF NOT EXISTS `jos_session` (
`username` varchar(150) DEFAULT '',
`time` varchar(14) DEFAULT '',
`session_id` varchar(200) NOT NULL DEFAULT '0',
`guest` tinyint(4) DEFAULT '1',
`userid` int(11) DEFAULT '0',
`usertype` varchar(50) DEFAULT '',
`gid` tinyint(3) unsigned NOT NULL DEFAULT '0',
`client_id` tinyint(3) unsigned NOT NULL DEFAULT '0',
`data` longtext,
PRIMARY KEY (`session_id`(64)),
KEY `whosonline` (`guest`,`usertype`),
KEY `userid` (`userid`),
KEY `time` (`time`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
我尝试将存储引擎更改为 InnoDB，但没有任何效果，我尝试优化表并删除了所有索引，但主索引。此表中有记录有存储空间
Data 12,352.0 KiB
Index 144.0 KiB
Total 12,496.0 KiB
我的服务器配置
auto_increment_increment 1
auto_increment_offset 1
autocommit ON
automatic_sp_privileges ON
back_log 50
basedir /usr
big_tables OFF
binlog_cache_size 32768
binlog_direct_non_transactional_uOFF
binlog_format STATEMENT
binlog_stmt_cache_size 32768
bulk_insert_buffer_size 8388608
character_set_client utf8
character_set_connection utf8
character_set_database latin1
character_set_filesystem binary
character_set_results utf8
character_set_server latin1
character_set_system utf8
character_sets_dir /usr/share/
collation_connection utf8_genera
collation_database latin1_swed
collation_server latin1_swed
completion_type NO_CHAIN
concurrent_insert AUTO
connect_timeout 10
datadir /var/lib/my
date_format %Y-%m-%d
datetime_format %Y-%m-%d %H
default_storage_engine InnoDB
default_week_format 0
delay_key_write ON
delayed_insert_limit 100
delayed_insert_timeout 300
delayed_queue_size 1000
div_precision_increment 4
engine_condition_pushdown ON
error_count 0
event_scheduler OFF
expire_logs_days 10
external_user
flush OFF
flush_time 0
foreign_key_checks ON
ft_boolean_syntax + -><()~*:"
ft_max_word_len 84
ft_min_word_len 4
ft_query_expansion_limit 20
ft_stopword_file (built-in)
general_log OFF
general_log_file /var/lib/my
group_concat_max_len 1024
have_compress YES
have_crypt YES
have_csv YES
have_dynamic_loading YES
have_geometry YES
have_innodb YES
have_ndbcluster NO
have_openssl DISABLED
have_partitioning YES
have_profiling YES
have_query_cache YES
have_rtree_keys YES
have_ssl DISABLED
have_symlink YES
hostname nzs2.automa
identity 0
ignore_builtin_innodb OFF
init_connect
init_file
init_slave
innodb_adaptive_flushing ON
innodb_adaptive_hash_index ON
innodb_additional_mem_pool_size 8388608
innodb_autoextend_increment 8
innodb_autoinc_lock_mode 1
innodb_buffer_pool_instances 1
innodb_buffer_pool_size 268435456
innodb_change_buffering all
innodb_checksums ON
innodb_commit_concurrency 0
innodb_concurrency_tickets 500
innodb_data_file_path ibdata1:10M
innodb_data_home_dir
innodb_doublewrite ON
innodb_fast_shutdown 1
innodb_file_format Antelope
innodb_file_format_check ON
innodb_file_format_max Antelope
innodb_file_per_table OFF
innodb_flush_log_at_trx_commit 1
innodb_flush_method
innodb_force_load_corrupted OFF
innodb_force_recovery 0
innodb_io_capacity 200
innodb_large_prefix OFF
innodb_lock_wait_timeout 50
innodb_locks_unsafe_for_binlog OFF
innodb_log_buffer_size 8388608
Variable_name Value
innodb_log_file_size 5242880
innodb_log_files_in_group 2
innodb_log_group_home_dir ./
innodb_max_dirty_pages_pct 75
innodb_max_purge_lag 0
innodb_mirrored_log_groups 1
innodb_old_blocks_pct 37
innodb_old_blocks_time 0
innodb_open_files 300
innodb_purge_batch_size 20
innodb_purge_threads 0
innodb_random_read_ahead OFF
innodb_read_ahead_threshold 56
innodb_read_io_threads 4
innodb_replication_delay 0
innodb_rollback_on_timeout OFF
innodb_rollback_segments 128
innodb_spin_wait_delay 6
innodb_stats_method nulls_equal
innodb_stats_on_metadata ON
innodb_stats_sample_pages 8
innodb_strict_mode OFF
innodb_support_xa ON
innodb_sync_spin_loops 30
innodb_table_locks ON
innodb_thread_concurrency 0
innodb_thread_sleep_delay 10000
innodb_use_native_aio OFF
innodb_use_sys_malloc ON
innodb_version 1.1.8
innodb_write_io_threads 4
insert_id 0
interactive_timeout 28800
join_buffer_size 262144
keep_files_on_create OFF
key_buffer_size 268435456
key_cache_age_threshold 300
key_cache_block_size 1024
key_cache_division_limit 100
large_files_support ON
large_page_size 0
large_pages OFF
last_insert_id 0
lc_messages en_US
lc_messages_dir /usr/share/
lc_time_names en_US
license GPL
local_infile ON
lock_wait_timeout 31536000
locked_in_memory OFF
log OFF
log_bin OFF
log_bin_trust_function_creators OFF
log_error
log_output FILE
log_queries_not_using_indexes OFF
log_slave_updates OFF
log_slow_queries ON
log_warnings 1
long_query_time 0.6
low_priority_updates OFF
lower_case_file_system OFF
lower_case_table_names 0
max_allowed_packet 16777216
max_binlog_cache_size ###
max_binlog_size 104857600
max_binlog_stmt_cache_size ###
max_connect_errors 10
max_connections 100
max_delayed_threads 20
max_error_count 64
max_heap_table_size 25165824
max_insert_delayed_threads 20
max_join_size ###
max_length_for_sort_data 1024
max_long_data_size 16777216
max_prepared_stmt_count 16382
max_relay_log_size 0
max_seeks_for_key ###
max_sort_length 1024
max_sp_recursion_depth 0
max_tmp_tables 32
max_user_connections 0
max_write_lock_count ###
metadata_locks_cache_size 1024
min_examined_row_limit 0
multi_range_count 256
myisam_data_pointer_size 6
myisam_max_sort_file_size ###
myisam_mmap_size ###
myisam_recover_options BACKUP
myisam_repair_threads 1
myisam_sort_buffer_size 8388608
myisam_stats_method nulls_unequ
myisam_use_mmap OFF
net_buffer_length 16384
net_read_timeout 30
net_retry_count 10
net_write_timeout 60
new OFF
Variable_name Value
old OFF
old_alter_table OFF
old_passwords OFF
open_files_limit 2158
optimizer_prune_level 1
optimizer_search_depth 62
optimizer_switch index_merge
performance_schema OFF
performance_schema_events_waits_h 10000
performance_schema_events_waits_h 10
performance_schema_max_cond_class 80
performance_schema_max_cond_insta 1000
performance_schema_max_file_class 50
performance_schema_max_file_handl 32768
performance_schema_max_file_insta 10000
performance_schema_max_mutex_clas 200
performance_schema_max_mutex_inst 1000000
performance_schema_max_rwlock_cla 30
performance_schema_max_rwlock_ins 1000000
performance_schema_max_table_hand 100000
performance_schema_max_table_inst 50000
performance_schema_max_thread_cla 50
performance_schema_max_thread_ins 1000
pid_file /var/run/my
plugin_dir /usr/lib/my
port 3306
preload_buffer_size 32768
profiling OFF
profiling_history_size 15
protocol_version 10
proxy_user
pseudo_thread_id 401326
query_alloc_block_size 8192
query_cache_limit 1048576
query_cache_min_res_unit 4096
query_cache_size 25165824
query_cache_type ON
query_cache_wlock_invalidate OFF
query_prealloc_size 8192
rand_seed1 0
rand_seed2 0
range_alloc_block_size 4096
read_buffer_size 131072
read_only OFF
read_rnd_buffer_size 262144
relay_log
relay_log_index
relay_log_info_file relay-log.i
relay_log_purge ON
relay_log_recovery OFF
relay_log_space_limit 0
report_host
report_password
report_port 3306
report_user
rpl_recovery_rank 0
secure_auth OFF
secure_file_priv
server_id 0
skip_external_locking ON
skip_name_resolve OFF
skip_networking OFF
skip_show_database OFF
slave_compressed_protocol OFF
slave_exec_mode STRICT
slave_load_tmpdir /tmp
slave_max_allowed_packet 1073741824
slave_net_timeout 3600
slave_skip_errors OFF
slave_transaction_retries 10
slave_type_conversions
slow_launch_time 2
slow_query_log ON
slow_query_log_file /var/log/my
socket /var/run/my
sort_buffer_size 2097152
sql_auto_is_null OFF
sql_big_selects ON
sql_big_tables OFF
sql_buffer_result OFF
sql_log_bin ON
sql_log_off OFF
sql_low_priority_updates OFF
sql_max_join_size ###
sql_mode
sql_notes ON
sql_quote_show_create ON
sql_safe_updates OFF
sql_select_limit ###
sql_slave_skip_counter 0
sql_warnings OFF
ssl_ca
ssl_capath
ssl_cert
ssl_cipher
ssl_key
storage_engine InnoDB
stored_program_cache 256
sync_binlog 0
sync_frm ON
Variable_name Value
sync_master_info 0
sync_relay_log 0
sync_relay_log_info 0
system_time_zone NZDT
table_definition_cache 1024
table_open_cache 1024
thread_cache_size 8
thread_concurrency 10
thread_handling one-thread-
thread_stack 196608
time_format %H:%i:%s
time_zone SYSTEM
timed_mutexes OFF
timestamp 1361481911
tmp_table_size 16777216
tmpdir /tmp
transaction_alloc_block_size 8192
transaction_prealloc_size 4096
tx_isolation REPEATABLE-
unique_checks ON
updatable_views_with_limit YES
version 5.5.29-0ubu
version_comment (Ubuntu)
version_compile_machine x86_64
version_compile_os debian-linu
wait_timeout 28800
warning_count 0
如何提高这些查询的速度？
一个典型的查询是这样的
UPDATE `jos_session`
SET `time`='1361469848',`userid`='0',`usertype`='',`username`='',
`gid`='0',`guest`='1',`client_id`='0',
`data`='__default|a:8:{s:15:\"session.counter\";i:1;s:19:\"session.timer.start\";i:1361469848;s:18:\"session.timer.last\";i:1361469848;s:17:\"session.timer.now\";i:1361469848;s:24:\"session.client.forwarded\";s:28:\"121.205.249.235, 23.15.14.22\";s:22:\"session.client.browser\";s:69:\"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.1.4322)\";s:8:\"registry\";O:9:\"JRegistry\":3:{s:17:\"_defaultNameSpace\";s:7:\"session\";s:9:\"_registry\";a:2:{s:7:\"session\";a:1:{s:4:\"data\";O:8:\"stdClass\":0:{}}s:11:\"application\";a:1:{s:4:\"data\";O:8:\"stdClass\":1:{s:4:\"lang\";s:5:\"en-GB\";}}}s:7:\"_errors\";a:0:{}}s:4:\"user\";O:5:\"JUser\":19:{s:2:\"id\";i:0;s:4:\"name\";N;s:8:\"username\";N;s:5:\"email\";N;s:8:\"password\";N;s:14:\"password_clear\";s:0:\"\";s:8:\"usertype\";N;s:5:\"block\";N;s:9:\"sendEmail\";i:0;s:3:\"gid\";i:0;s:12:\"registerDate\";N;s:13:\"lastvisitDate\";N;s:10:\"activation\";N;s:6:\"params\";N;s:3:\"aid\";i:0;s:5:\"guest\";i:1;s:7:\"_params\";O:10:\"JParameter\":7:{s:4:\"_raw\";s:0:\"\";s:4:\"_xml\";N;s:9:\"_elements\";a:0:{}s:12:\"_elementPath\";a:1:{i:0;s:69:\"/var/www/www.seleconlight.com/libraries/joomla/html/parameter/element\";}s:17:\"_defaultNameSpace\";s:8:\"_default\";s:9:\"_registry\";a:1:{s:8:\"_default\";a:1:{s:4:\"data\";O:8:\"stdClass\":0:{}}}s:7:\"_errors\";a:0:{}}s:9:\"_errorMsg\";N;s:7:\"_errors\";a:0:{}}}country_cc|N;'
WHERE session_id='k3fuukvh8lrfq244u6ic4it605';
首先 在 my.cnf 中设置 query_cache_type=0 和 query_cache_size=0 对于多核系统，缓存会产生争用问题。
重要问题 您的服务器上显示了多少可用 RAM（使用 top 命令）？慢查询日志中显示的特定语句是什么？
如果您要将表数据库引擎保留为 InnoDB，我建议您 Make innodb_log_file_size = innodb_buffer_pool_size/2 这将减少 IO。请务必遵循此处的说明：http: //dev.mysql.com/doc/refman/5.5/en/innodb-data-log-reconfiguration.html 在以“如果您想更改”开头的地方。
如果您想将其保留为 MyISAM， 此表将在每次更新时被锁定。将 varchars 和 longtext 更改为 chars，使其成为一个固定长度的表（参见http://dev.mysql.com/doc/refman/5.5/en/myisam-table-formats.html
更改主键以使用哈希索引：
关于查询缓存 查询缓存的长篇大论；如果您一遍又一遍地运行相同的选择查询，那么它可以提供帮助，但是运行它会产生很多开销。一般规则，将其关闭，然后在需要时将其打开。（见http://www.mysqlperformanceblog.com/2006/07/27/mysql-query-cache/）
加快更新 * 感谢慢查询日志语句。减慢更新的最大因素是更新索引。由于您已尝试删除索引，因此下一步是将表转换为 InnoDB 引擎。MyISAM 在并发更新方面不是很好。如果仍然不满意，下一步看看你是否不能在不同的设备上对表进行分区，但要确保额外的管理负担是值得的。您是否有任何额外的硬盘设备可供未使用的服务器使用？
Joomla 会话表 经调查，该表被删除，这意味着它会有漏洞。如果您仍想坚持使用 MyISAM，请尝试设置 concurrent_insert=2。您可以在不需要维护窗口的情况下执行此操作。（更多信息：http ://dev.mysql.com/doc/refman/5.5/en/concurrent-inserts.html ）。INSERTS 比更新具有更高的优先级，因此加快这些速度可能会加快您的 UPDATE 语句。
内存和 InnoDB 如果您可以将 innodb_buffer_pool_size 设置为数据库的总大小 + 所有 InnoDB 表的索引，那么更新将首先发生在 RAM 中而不是磁盘中。这是性能的理想选择。由于我看到您在服务器上使用了大约 2.7GB，因此可能还有其他应用程序争用磁盘 - 更多的是使用 innodb 缓冲区设置进入 innodb。