mysql 性能/缓存配置之谜

Question

mysql 性能/缓存配置之谜

我有两个 mysql 5.1 实例（比如 A、B）托管相同的数据库架构。如果我在两个实例上运行（使用 mysql 工作台）相同的查询，我不明白为什么我在后续请求中得到非常不同的响应时间。

在实例 A 上，第一次查询执行需要 0.688 秒，第二次查询执行需要 0.683 秒
在实例 B 上，第一次查询执行需要 0.688 秒，第二次查询执行需要 0.027 秒

看起来两个实例之间存在缓存配置差异，但我找不到它。

比较SHOW VARIABLES两个实例的结果只给出了几个不同的值（我看不出它们如何影响查询执行时间）：

general_log_file :  
/path/to/file2.log    VS    /path/to/file1.log  

hostname :  
mysql2    VS    mysql1  

pid_file :  
/var/lib/mysql/mysql2.pid    VS    /var/lib/mysql/mysql1.pid  

slave_max_allowed_packet :  
1073741824    VS    (empty)  

slow_query_log_file :  
/var/lib/mysql/mysql2-slow.log   VS   /var/lib/mysql/mysql1-slow.log  

system_time_zone :  
CET   VS  CEST  

timestamp :  
1352219171   VS   1352219229  

version :  
5.1.66-0ubuntu0.10.04.1   VS   5.1.62-0ubuntu0.10.04.1

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顺便提一下，实例A是我们的测试环境，实例B是我们的生产环境

编辑：（@Rick James 推荐）

以下变量在两种环境中严格相同

SHOW VARIABLES LIKE '%buffer%'

bulk_insert_buffer_size 8388608
innodb_buffer_pool_size 8388608
innodb_log_buffer_size  1048576
join_buffer_size    131072
key_buffer_size 16777216
myisam_sort_buffer_size 8388608
net_buffer_length   16384
preload_buffer_size 32768
read_buffer_size    131072
read_rnd_buffer_size    262144
sort_buffer_size    2097144
sql_buffer_result   OFF


SHOW VARIABLES LIKE 'innodb%'

innodb_adaptive_hash_index  ON
innodb_additional_mem_pool_size 1048576
innodb_autoextend_increment 8
innodb_autoinc_lock_mode    1
innodb_buffer_pool_size 8388608
innodb_checksums    ON
innodb_commit_concurrency   0
innodb_concurrency_tickets  500
innodb_data_file_path   ibdata1:10M:autoextend
innodb_data_home_dir    
innodb_doublewrite  ON
innodb_fast_shutdown    1
innodb_file_io_threads  4
innodb_file_per_table   OFF
innodb_flush_log_at_trx_commit  1
innodb_flush_method 
innodb_force_recovery   0
innodb_lock_wait_timeout    50
innodb_locks_unsafe_for_binlog  OFF
innodb_log_buffer_size  1048576
innodb_log_file_size    5242880
innodb_log_files_in_group   2
innodb_log_group_home_dir   ./
innodb_max_dirty_pages_pct  90
innodb_max_purge_lag    0
innodb_mirrored_log_groups  1
innodb_open_files   300
innodb_rollback_on_timeout  OFF
innodb_stats_method nulls_equal
innodb_stats_on_metadata    ON
innodb_support_xa   ON
innodb_sync_spin_loops  20
innodb_table_locks  ON
innodb_thread_concurrency   8
innodb_thread_sleep_delay   10000
innodb_use_legacy_cardinality_algorithm ON

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实际的 SELECT ：

select
    post0_.id as id83_0_,
    thread1_.id as id81_1_,
    post0_.createDate as createDate83_0_,
    post0_.editCount as editCount83_0_,
    post0_.editDate as editDate83_0_,
    post0_.editor_id as editor7_83_0_,
    post0_.postType as postType83_0_,
    post0_.poster_id as poster8_83_0_,
    post0_.repliedTo_id as repliedTo9_83_0_,
    post0_.text as text83_0_,
    post0_.thread_id as thread10_83_0_,
    thread1_.created as created81_1_,
    thread1_.debate_id as debate16_81_1_,
    thread1_.description as descript4_81_1_,
    thread1_.lastPostDate as lastPost5_81_1_,
    thread1_.poster_id as poster17_81_1_,
    thread1_.status as status81_1_,
    thread1_.threadType as threadType81_1_,
    thread1_.title as title81_1_,
    thread1_.updated as updated81_1_,
    thread1_.viewCount as viewCount81_1_,
    thread1_.imageUrl as imageUrl81_1_,
    thread1_.mediaTypeValue as mediaTy11_81_1_,
    thread1_.mediaUrl as mediaUrl81_1_,
    thread1_.modoWeight as modoWeight81_1_,
    thread1_.shortName as shortName81_1_,
    thread1_.why as why81_1_,
    thread1_.theme_id as theme18_81_1_,
    thread1_.answer_debaterId as answer19_81_1_,
    thread1_.answer_pollId as answer20_81_1_,
    (SELECT
        COUNT(*) 
    FROM
        Post p 
    WHERE
        p.thread_id = thread1_.id) as formula9_1_ 
from
    Post post0_ 
inner join
    Thread thread1_ 
        on post0_.thread_id=thread1_.id 
where
    post0_.postType in (
        'P', 'F'
    ) 
    and thread1_.debate_id=69 
    and thread1_.threadType<>'B' 
    and length(post0_.text)>0 
order by
    createDate desc limit 5

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EXPLAIN SELECT（在两种环境中都是相同的）：

id  select_type table   type    possible_keys   key key_len ref rows    Extra
1   PRIMARY thread1_    ref PRIMARY,FK9545FA2AEBB74893  FK9545FA2AEBB74893  5   const   3690    Using where; Using temporary; Using filesort
1   PRIMARY post0_  ref FK260CC0D74BC5F3    FK260CC0D74BC5F3    5   debate-atest.thread1_.id    2   Using where
2   DEPENDENT SUBQUERY  p   ref FK260CC0D74BC5F3    FK260CC0D74BC5F3    5   debate-atest.thread1_.id    2   Using where; Using index

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CREATE TABLE STATEMENT（除了约束名称外，两者完全相同）：

delimiter $$

CREATE TABLE `Post` (
  `postType` varchar(1) NOT NULL,
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `createDate` datetime DEFAULT NULL,
  `editCount` int(11) NOT NULL,
  `editDate` datetime DEFAULT NULL,
  `text` longtext,
  `editor_id` int(11) DEFAULT NULL,
  `poster_id` int(11) DEFAULT NULL,
  `repliedTo_id` int(11) DEFAULT NULL,
  `thread_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `createDateIx` (`createDate`),
  KEY `FK260CC0D74BC5F3` (`thread_id`),
  KEY `FK260CC07C1A4F95` (`poster_id`),
  KEY `FK260CC0960B3775` (`editor_id`),
  KEY `FK260CC0D7C95B5F` (`repliedTo_id`),
  CONSTRAINT `FK260CC0D7C95B5F` FOREIGN KEY (`repliedTo_id`) REFERENCES `Post` (`id`),
  CONSTRAINT `FK260CC07C1A4F95` FOREIGN KEY (`poster_id`) REFERENCES `Debater` (`id`),
  CONSTRAINT `FK260CC0960B3775` FOREIGN KEY (`editor_id`) REFERENCES `Debater` (`id`),
  CONSTRAINT `FK260CC0D74BC5F3` FOREIGN KEY (`thread_id`) REFERENCES `Thread` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=148523 DEFAULT CHARSET=utf8$$

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和

delimiter $$

CREATE TABLE `Thread` (
  `threadType` varchar(1) NOT NULL,
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `created` datetime DEFAULT NULL,
  `description` varchar(700) DEFAULT NULL,
  `lastPostDate` datetime DEFAULT NULL,
  `status` int(11) NOT NULL,
  `title` varchar(100) DEFAULT NULL,
  `updated` datetime DEFAULT NULL,
  `viewCount` int(11) NOT NULL,
  `imageUrl` varchar(255) DEFAULT NULL,
  `mediaTypeValue` int(11) DEFAULT NULL,
  `mediaUrl` varchar(1000) DEFAULT NULL,
  `modoWeight` int(11) DEFAULT NULL,
  `shortName` varchar(15) DEFAULT NULL,
  `why` longtext,
  `debate_id` int(11) DEFAULT NULL,
  `poster_id` int(11) DEFAULT NULL,
  `theme_id` int(11) DEFAULT NULL,
  `answer_debaterId` int(11) DEFAULT NULL,
  `answer_pollId` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `answerPollIx` (`answer_pollId`),
  KEY `FK9545FA2AAF24B581` (`theme_id`),
  KEY `FK9545FA2A7C1A4F95` (`poster_id`),
  KEY `FK9545FA2AEBB74893` (`debate_id`),
  KEY `FK9545FA2A82957DB8` (`answer_debaterId`,`answer_pollId`),
  CONSTRAINT `FK9545FA2A82957DB8` FOREIGN KEY (`answer_debaterId`, `answer_pollId`) REFERENCES `Answer` (`debaterId`, `pollId`),
  CONSTRAINT `FK9545FA2A7C1A4F95` FOREIGN KEY (`poster_id`) REFERENCES `Debater` (`id`),
  CONSTRAINT `FK9545FA2AAF24B581` FOREIGN KEY (`theme_id`) REFERENCES `Thread` (`id`),
  CONSTRAINT `FK9545FA2AEBB74893` FOREIGN KEY (`debate_id`) REFERENCES `Debate` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=49829 DEFAULT CHARSET=utf8$$

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Answer 1

Ric*_*mes 1

显示类似“%buffer%”的变量；-- 不要相信 my.cnf

显示类似“innodb%”的变量；

让我们看看实际的 SELECT —— 那里可能有线索。

EXPLAIN SELECT——在每台机器上。

显示创建表

然后在两台机器之间进行比较。如果这不能告诉您问题是什么，请向我们展示输出，突出显示差异。

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