Query optimization concerns how to improve the performance of slow queries.
查询优化涉及到了怎样改进慢速查询的问题。
Therefore, if a query filter field is one of these types, and the associated table is large, the query can be very slow.
因此，如果查询筛选字段是这种类型中的一个，而相关的表格很大，那么查询的速度会非常慢。
To see if local processing is occurring for a slow performing query, there are a couple of troubleshooting techniques.
我们可以利用两个故障修复技术来了解一个执行速度较慢的查询中是否进行了本地处理。
Based on the information available in that report, you can discover whether the problem is a result of slow PHP execution or a slow query.
根据报告中的可用信息，您就可以发现问题是由PHP执行慢还是查询慢引起的。
A query is often slow because it has no index or an inefficient index.
查询很慢，因为没有索引或者索引不足够。
As you can see, the query was executed three times, and the average elapsed time is about 307 seconds, which is very slow.
如您所见，查询执行了三次，平均运行时间大约是307秒，非常慢。
Slow SQL is usually caused by an inefficient WHERE clause, which corresponds to inefficient query filter definition in ClearQuest.
慢速SQL通常是由where语句不够，它对应于ClearQuest中查询筛选定义不够。
You can configure mysqld to log slow queries in the aptly named slow query log.
您可以配置mysqld将这些慢速查询记录到适当命名的慢速查询日志中。
A slow ClearQuest query is generally caused by underlying SQL syntax that is slow.
慢速clearquest查询通常是由慢速的sql语法造成的。
Listing 1 shows the configuration required in my.cnf to enable the slow query log.
清单1给出了要启用慢速查询日志需要在my .cnf中所做的配置。
Reading through the slow query log is best done with the mysqldumpslow command.
阅读慢速查询日志最好是通过mysqldumpslow命令进行。
Secondly, returning many empty rows makes this query needlessly slow.
其次，返回很多空行使查询速度不必要地慢了下来。
For example, simple EXPLAIN statements in the queries and a large amount of query log analysis will slow down the queries.
例如，查询中简单的explain语句和大量的查询日志分析将使查询变得缓慢。
The query optimizer also tries to reduce the number of messages sent to the data source if the network is slow.
如果网络较慢，查询优化器还尝试减少发送到数据源的消息数量。
Creating and manipulating large quantities of ActiveRecord objects can be slow, so in some cases, it can be much faster to write a SQL query directly that does not instantiate any objects.
创建和处理数量巨大的ActiveRecord对象的速度会非常缓慢，所以在有些情况下，直接编写一个无需实例化任何对象的SQL查询会更快些。
A large DSS query by the QC agent will just waste cycles and slow everyone else down.
QC代理运行的大型DSS查询会浪费CPU周期，从而降低其他查询的速度。
In some cases, joining on unindexed columns can result in a slow query.
在某些情况下，联接非索引列会使查询速度变慢。
If the slow query log is enabled, the query is logged to the slow query log file.
如果启用了慢查询日志，则查询将记录到慢查询日志文件中。
If the slow query log is enabled, the query is logged to the slow query log file.
如果启用了慢查询日志，则查询将记录到慢查询日志文件中。
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