SQL请求优化

Question

我有一个SQL请求,它在工作时占用了我100%的VM CPU.我想知道如何优化它:

SELECT g.name AS hostgroup
     , h.name AS hostname
     , a.host_id
     , s.display_name AS servicename
     , a.service_id
     , a.entry_time AS ack_time
     , (  SELECT ctime 
          FROM logs 
          WHERE logs.host_id = a.host_id 
          AND logs.service_id = a.service_id 
          AND logs.ctime < a.entry_time 
          AND logs.status IN (1, 2, 3) 
          AND logs.type = 1 
          ORDER BY logs.log_id DESC 
          LIMIT 1) AS start_time
     , ar.acl_res_name AS timeperiod
     , a.state AS state
     , a.author
     , a.acknowledgement_id AS ack_id
FROM centstorage.acknowledgements a
LEFT JOIN centstorage.hosts h ON a.host_id = h.host_id
LEFT JOIN centstorage.services s ON a.service_id = s.service_id
LEFT JOIN centstorage.hosts_hostgroups p ON a.host_id = p.host_id
LEFT JOIN centstorage.hostgroups g ON  g.hostgroup_id = p.hostgroup_id
LEFT JOIN centreon.hostgroup_relation hg ON a.host_id = hg.host_host_id
LEFT JOIN centreon.acl_resources_hg_relations hh ON hg.hostgroup_hg_id = hh.hg_hg_id
LEFT JOIN centreon.acl_resources ar ON hh.acl_res_id = ar.acl_res_id
WHERE ar.acl_res_name != 'All Resources'
AND YEAR(FROM_UNIXTIME( a.entry_time )) = YEAR(CURDATE())
AND MONTH(FROM_UNIXTIME( a.entry_time )) = MONTH(CURDATE())
AND a.service_id is not null
ORDER BY a.acknowledgement_id ASC

问题出在这一部分:

(SELECT ctime FROM logs
 WHERE logs.host_id = a.host_id
   AND logs.service_id = a.service_id
   AND logs.ctime < a.entry_time
   AND logs.status IN (1, 2, 3)
   AND logs.type = 1
 ORDER BY logs.log_id DESC
 LIMIT 1) AS start_time

表日志真的很大,一些朋友告诉我使用缓冲表/数据库,但我很清楚这些事情,我不知道该怎么做.

有一个EXPLAIN EXTENDED查询:

看来他只会检查2行表日志,为什么需要这么多时间呢？(表日志中有560000行).

以下是这些表的所有索引:

centstorage.acknowledgements:

centstorage.hosts:

centstorage.services:

centstorage.hosts_hostgroups:

centstorage.hostgroups:

centreon.hostgroup_relation:

centreon.acl_resources_hg_relations:

centreon.acl_resources:

Answer 1

因为SQL Server可以使用以下命令定义查询的最大并行度MAXDOP

例如，您可以在查询末尾定义

option (maxdop 2) 

我很确定 中有一个等效的东西MySql。

如果执行时间不相关，您可以尝试处理这种情况。