MySQL 性能和变量调整

MySQL 性能和变量调整

我遇到的问题

我的 MySql 服务器有问题，导致它一直冻结。在 phpMyAdmin 中，当这种情况发生时，我可以在“显示进程列表”中看到许多用户“未经身份验证的用户”的进程，命令“连接”和状态“从网络读取”。

数据库使用 InnoDB，但我也使用一个运行 MyISAM 的表来执行全文搜索。服务器内存约为 4GB，使用时不到 500MB。

我一直在使用 MySQL 中的慢速查询日志来查找不使用索引的查询。我还认为我需要对服务器变量进行一些更改/调整。

我真的可以在这里使用一些帮助，因此我在这里发布了 SHOW GLOBAL STATUS 和 SHOW GLOBAL VARIABLES，也许您可以给我一些想法，我应该如何设置变量？

当前显示全局状态：

-- Source - https://stackoverflow.com/q
-- Posted by Martin, modified by community. See post 'Timeline' for change history
-- Retrieved 2025-11-12, License - CC BY-SA 3.0

Variable_name   Value
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Sort_scan   757681
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Ssl_version     
Table_locks_immediate   51310065
Variable_name   Value
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Tc_log_page_size    0
Tc_log_page_waits   0
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Threads_running     1
Uptime  1208447
Uptime_since_flush_status   1208447

当前显示全局变量：

-- Source - https://stackoverflow.com/q
-- Posted by Martin, modified by community. See post 'Timeline' for change history
-- Retrieved 2025-11-12, License - CC BY-SA 3.0

Variable_name   Value
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_updates     OFF
binlog_format   STATEMENT
binlog_stmt_cache_size  32768
bulk_insert_buffer_size     8388608
character_set_client    latin1
character_set_connection    latin1
character_set_database  latin1
character_set_filesystem    binary
character_set_results   latin1
character_set_server    latin1
character_set_system    utf8
character_sets_dir  /usr/share/mysql/charsets/
collation_connection    latin1_swedish_ci
collation_database  latin1_swedish_ci
collation_server    latin1_swedish_ci
completion_type     NO_CHAIN
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datadir     /var/lib/mysql/
date_format     %Y-%m-%d
datetime_format     %Y-%m-%d %H:%i:%s
default_storage_engine  InnoDB
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flush   OFF
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ft_stopword_file    (built-in)
general_log     OFF
general_log_file    /var/lib/mysql/db.log
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    silldb5
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init_connect    
init_file   
init_slave  
innodb_adaptive_flushing    ON
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innodb_change_buffering     all
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innodb_data_file_path   ibdata1:10M:autoextend
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     
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innodb_force_recovery   0
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innodb_large_prefix     OFF
innodb_lock_wait_timeout    50
innodb_locks_unsafe_for_binlog  OFF
innodb_log_buffer_size  8388608
innodb_log_file_size    5242880
innodb_log_files_in_group   2
innodb_log_group_home_dir   ./
Variable_name   Value
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
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innodb_random_read_ahead    OFF
innodb_read_ahead_threshold     56
innodb_read_io_threads  4
innodb_replication_delay    0
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innodb_rollback_segments    128
innodb_spin_wait_delay  6
innodb_stats_method     nulls_equal
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innodb_support_xa   ON
innodb_sync_spin_loops  30
innodb_table_locks  ON
innodb_thread_concurrency   0
innodb_thread_sleep_delay   10000
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innodb_use_sys_malloc   ON
innodb_version  1.1.8
innodb_write_io_threads     4
interactive_timeout     28800
join_buffer_size    131072
keep_files_on_create    OFF
key_buffer_size     16384
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
lc_messages     en_US
lc_messages_dir     /usr/share/mysql/
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   /var/lib/mysql/db.err
log_output  FILE
log_queries_not_using_indexes   OFF
log_slave_updates   OFF
log_slow_queries    OFF
log_warnings    1
long_query_time     10.000000
low_priority_updates    OFF
lower_case_file_system  OFF
lower_case_table_names  0
max_allowed_packet  1048576
max_binlog_cache_size   18446744073709547520
max_binlog_size     1073741824
max_binlog_stmt_cache_size  18446744073709547520
max_connect_errors  10
max_connections     2000
max_delayed_threads     20
max_error_count     64
max_heap_table_size     16777216
max_insert_delayed_threads  20
max_join_size   18446744073709551615
max_length_for_sort_data    1024
max_long_data_size  1048576
max_prepared_stmt_count     16382
max_relay_log_size  0
max_seeks_for_key   18446744073709551615
max_sort_length     1024
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max_user_connections    0
max_write_lock_count    18446744073709551615
metadata_locks_cache_size   1024
min_examined_row_limit  0
multi_range_count   256
myisam_data_pointer_size    6
myisam_max_sort_file_size   9223372036853727232
myisam_mmap_size    18446744073709551615
myisam_recover_options  OFF
myisam_repair_threads   1
myisam_sort_buffer_size     8388608
myisam_stats_method     nulls_unequal
myisam_use_mmap     OFF
net_buffer_length   2048
net_read_timeout    30
net_retry_count     10
net_write_timeout   60
new     OFF
old     OFF
old_alter_table     OFF
old_passwords   OFF
open_files_limit    10000
optimizer_prune_level   1
Variable_name   Value
optimizer_search_depth  62
optimizer_switch    index_merge=on,index_merge_union=on,index_merge_so...
performance_schema  OFF
performance_schema_events_waits_history_long_size   10000
performance_schema_events_waits_history_size    10
performance_schema_max_cond_classes     80
performance_schema_max_cond_instances   1000
performance_schema_max_file_classes     50
performance_schema_max_file_handles     32768
performance_schema_max_file_instances   10000
performance_schema_max_mutex_classes    200
performance_schema_max_mutex_instances  1000000
performance_schema_max_rwlock_classes   30
performance_schema_max_rwlock_instances     1000000
performance_schema_max_table_handles    100000
performance_schema_max_table_instances  50000
performance_schema_max_thread_classes   50
performance_schema_max_thread_instances     1000
pid_file    /var/run/mysqld/mysqld.pid
plugin_dir  /usr/lib64/mysql/plugin
port    3306
preload_buffer_size     32768
profiling   OFF
profiling_history_size  15
protocol_version    10
query_alloc_block_size  8192
query_cache_limit   1048576
query_cache_min_res_unit    4096
query_cache_size    8 388 608
query_cache_type    ON
query_cache_wlock_invalidate    OFF
query_prealloc_size     8192
range_alloc_block_size  4096
read_buffer_size    262144
read_only   OFF
read_rnd_buffer_size    262144
relay_log   
relay_log_index     
relay_log_info_file     relay-log.info
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   1
skip_external_locking   ON
skip_name_resolve   ON
skip_networking     OFF
skip_show_database  OFF
slave_compressed_protocol   OFF
slave_exec_mode     STRICT
slave_load_tmpdir   /tmp
slave_net_timeout   3600
slave_skip_errors   OFF
slave_transaction_retries   10
slave_type_conversions  
slow_launch_time    2
slow_query_log  OFF
slow_query_log_file     /var/lib/mysql/slow.log
socket  /var/lib/mysql/mysql.sock
sort_buffer_size    65536
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   18446744073709551615
sql_mode    
sql_notes   ON
sql_quote_show_create   ON
sql_safe_updates    OFF
sql_select_limit    18446744073709551615
sql_slave_skip_counter  0
sql_warnings    OFF
ssl_ca  
ssl_capath  
ssl_cert    
ssl_cipher  
ssl_key     
storage_engine  InnoDB
sync_binlog     0
sync_frm    ON
sync_master_info    0
sync_relay_log  0
sync_relay_log_info     0
system_time_zone    CET
table_definition_cache  400
table_open_cache    4
thread_cache_size   100
thread_concurrency  8
thread_handling     one-thread-per-connection
thread_stack    524288
time_format     %H:%i:%s
Variable_name   Value
time_zone   SYSTEM
timed_mutexes   OFF
tmp_table_size  16777216
tmpdir  /tmp
transaction_alloc_block_size    8192
transaction_prealloc_size   4096
tx_isolation    REPEATABLE-READ
unique_checks   ON
updatable_views_with_limit  YES
version     5.5.20
version_comment     MySQL Community Server (GPL) by Remi
version_compile_machine     x86_64
version_compile_os  Linux
wait_timeout    28800

解决

优化 mysql 在网上可以找到关于如何做到这一点的大量信息。从来没有“最佳参数”，最好的参数是那些适合你需求的参数… 因此，我们不会给出最佳参数，而是给出如何定义这些参数。做一些测试，你很快就会找到自己的参数。

有很多可用的参数，但只有少数一个对于调整您的 mysql 框非常重要。

最重要的变量是（对我来说，它并不详尽）：

-- Source - https://stackoverflow.com/a
-- Posted by Somnath Muluk, modified by community. See post 'Timeline' for change history
-- Retrieved 2025-11-12, License - CC BY-SA 3.0

-   max_connections
-   wait_timeout
-   thread_cache_size
-   table_cache
-   key_buffer_size
-   query_cache_size
-   tmp_table_size

要获取 mysql 服务器在加载后的统计信息，请如上所述运行 mysqladmin processlist extended-status。

1 – 两个最重要的变量：Table_cache和Key_buffer_size

如果Opened_tables很大，那么你的table_cache变量可能是 太小了。 table_cache 64 Open_tables 64 Opened_tables 544468
这是第一个严重的问题。“table_cache是开放的数量 所有线程的表。MySQL 是多线程的，可能运行许多 一次对表进行查询，每个查询都会打开一个表。 因此，即使我们只有几张桌子，我们也需要更多 open_tables。

Opened_tables值较高，并显示 缓存未命中。正确table_cache尺寸是两个最好的方法之一 您可以采取哪些措施来提高性能。

如果Key_reads很大，那么你的key_buffer_size变量可能是 太小了。缓存命中率可以通过以下方式计算 Key_reads/Key_read_requests。 key_buffer_size 16M Key_read_requests 2973620399 Key_reads 8490571 （缓存命中率 = 0.0028）
“key_buffer_size会影响索引缓冲区的大小和速度 索引处理，尤其是阅读。MySQL 手册（和其他来源）说 “Key_reads/Key_read_request比通常应< 0.01。”这是 其他最重要的事情要正确。这里的值似乎是正确的（< 0.01）

还要检查key_write_requests和key_writes。 key_writes/key_writes_request通常应该是 < 1（接近 0.5 似乎没问题）

2 – 其他重要设置是：Wait_timeout、max_connexion thread_cache

一点解释： 通常，您有很多 mysql 进程处于休眠状态，因为wait_timeout没有设置得很低。所以我确保将wait_timeout设置为一个非常低的值：15 秒（对我来说）。这意味着 MySQL 将关闭任何空闲超过 15 秒的连接。

问题是你还必须增加你的max_connexion（我的设置为 300），以确保没有很多空闲客户端持有连接并阻止新客户端连接和完成实际工作。 pbm 是盒子必须以非常高的速率创建新线程（MySQL 是一个多线程服务器）。这可能会占用大量可测量的 CPU 时间。

所以解决方案是使用Thread_cache（来自 mysql 文档）： “我们应该在缓存中保留多少个线程以供重用。当客户端断开连接时，如果之前的线程不超过 thread_cache_size，则客户端的线程将被放入缓存中。所有新线程都首先从缓存中获取，只有当缓存为空时才会创建新线程。如果您有很多新连接，可以增加此变量以提高性能。（通常，如果您有一个良好的线程实现，这不会带来显着的性能改进。通过检查 Connections 和 Threads_created 之间的差异，您可以了解当前线程缓存对您来说有多高效。

如果Threads_created很大，您可能需要增加 thread_cache_size变量。缓存命中率可以通过以下方式计算 Threads_created/连接。 thread_cache_size 0 Threads_created 150022 连接150023
这是第二个应该解决的问题。my-medium.cnf 的默认缓存大小为零，但 my-large.cnf 中的建议大小为 8。

您可以尝试以下公式：table_cache = 打开的表格 / max_used_connection

3 – 最后，您还可以看看：tmp_table_size 和 Handler_read_rnd / Handler_read_rnd_next

如果Created_tmp_disk_tables很大，您可能需要增加 tmp_table_size变量来获取基于内存的临时表 基于磁盘的。
tmp_table_size 32M Created_tmp_disk_tables 3227 Created_tmp_tables 159832 Created_tmp_files 4444

Created_tmp_disk_tables是“隐式临时表的数量 disk created while executing statements“，Created_tmp_tables是 基于内存。显然，如果您必须转到磁盘而不是磁盘，那就不好了 记忆。大约 2% 的临时表进入磁盘，这似乎还不错 但增加tmp_table_size可能也不会有什么坏处。

如果Handler_read_rnd很大，那么你可能有很多查询 需要 MySQL 扫描整个表，或者您有未使用 正确按键。 Handler_read_rnd 27712353 Handler_read_rnd_next 283536234
这些价值很高，我们可能会改进 索引和查询。

我希望这能帮助你们中的一些人更多地了解如何优化 MYSQL 以满足您的需求、硬感知框或 mysql 当前使用情况。