查询缓存效率

Question

我正在使用 MySQLTuner.pl 来优化我的网站......尽管我不完全确定如何解决其中一些问题，并且想知道是否有人可以帮助我。

我正在使用以下 MySQL 设置运行 16GB RAM：

key_buffer              = 1024M
max_allowed_packet      = 16M
thread_stack            = 192K
thread_cache_size       = 8

myisam-recover         = BACKUP
max_connections        = 1500
table_cache            = 256
thread_concurrency     = 4

query_cache_limit       = 2M
query_cache_size        = 32M
query_cache_type        = 1

tmp_table_size          = 512M
max_heap_table_size     = 128M
join_buffer_size        = 128M
myisam_sort_buffer_size = 512M

这是我的调优器的输出

   -------- General Statistics --------------------------------------------------
[--] Skipped version check for MySQLTuner script
[OK] Currently running supported MySQL version 5.1.41-3ubuntu12.6-log
[OK] Operating on 64-bit architecture

-------- Storage Engine Statistics -------------------------------------------
[--] Status: -Archive -BDB -Federated +InnoDB -ISAM -NDBCluster
[--] Data in MyISAM tables: 98M (Tables: 402)
[--] Data in InnoDB tables: 16K (Tables: 1)
[!!] Total fragmented tables: 17

-------- Performance Metrics -------------------------------------------------
[--] Up for: 10s (1K q [132.400 qps], 443 conn, TX: 119K, RX: 82K)
[--] Reads / Writes: 100% / 0%
[--] Total buffers: 1.2G global + 130.6M per thread (1500 max threads)
[!!] Maximum possible memory usage: 192.4G (1225% of installed RAM)
[OK] Slow queries: 0% (0/1K)
[OK] Highest usage of available connections: 0% (2/1500)
[OK] Key buffer size / total MyISAM indexes: 1.0G/72.5M
[!!] Key buffer hit rate: 72.3% (47 cached / 13 reads)
[!!] Query cache efficiency: 0.0% (0 cached / 875 selects)
[OK] Query cache prunes per day: 0
[OK] Sorts requiring temporary tables: 0% (0 temp sorts / 2 sorts)
[OK] Temporary tables created on disk: 23% (48 on disk / 201 total)
[OK] Thread cache hit rate: 99% (2 created / 443 connections)
[!!] Table cache hit rate: 4% (128 open / 2K opened)
[OK] Open file limit used: 3% (257/7K)
[OK] Table locks acquired immediately: 100% (449 immediate / 449 locks)
[OK] InnoDB data size / buffer pool: 16.0K/8.0M

-------- Recommendations -----------------------------------------------------
General recommendations:
    Run OPTIMIZE TABLE to defragment tables for better performance
    MySQL started within last 24 hours - recommendations may be inaccurate
    Reduce your overall MySQL memory footprint for system stability
    Increase table_cache gradually to avoid file descriptor limits
Variables to adjust:
  *** MySQL's maximum memory usage is dangerously high ***
  *** Add RAM before increasing MySQL buffer variables ***
    query_cache_limit (> 2M, or use smaller result sets)
    table_cache (> 128)

当我减少 query_cache_limit 和 table_cache 时，它似乎没有任何效果。我在过去 24 小时内重新启动了 MySQL，这可能是问题的一部分。

更新

运行SHOW STATUS LIKE '%cache%'后，输出为

Variable_name   Value
Binlog_cache_disk_use   0
Binlog_cache_use    0
Com_assign_to_keycache  0
Qcache_free_blocks  436
Qcache_free_memory  23551488
Qcache_hits 72553
Qcache_inserts  26954
Qcache_lowmem_prunes    0
Qcache_not_cached   7164
Qcache_queries_in_cache 5877
Qcache_total_blocks 12347
Ssl_callback_cache_hits 0
Ssl_session_cache_hits  0
Ssl_session_cache_misses    0
Ssl_session_cache_mode  NONE
Ssl_session_cache_overflows 0
Ssl_session_cache_size  0
Ssl_session_cache_timeouts  0
Ssl_used_session_cache_entries  0
Threads_cached  3

Answer 1

我发现这个网站有助于优化我自己的 mysql 服务器： http://www.omh.cc/mycnf/

它允许您调整变量并了解总内存容量。您需要优化 60% 的内存使用率。因此，请尝试将总内存占用量降低到总 RAM 的 60% 到 70% 左右。如果您在同一台机器上运行其他东西，您可能需要减少该数量。忘记查询缓存吧，它不会增加太多价值，但是如果做得好，表缓存应该会提高你的性能。

尝试减少连接数量并将总内存占用量保持在系统总内存的 60% 以下。