分类:
2009-08-13 22:56:22
In particular, estimates for full-text-search operators are greatly improved. 特
别是,全文搜索操作有极大的提升。
This means that these types of queries no longer automatically produce sorted output.
这意味着以上类型的查询不再进行排序(按我的理解,这使得查询操作并行化,特别对于分布到多个存储器上的数据库,性能会有提升明显——译者)。
This work formalizes our previous ad-hoc treatment of IN (SELECT ...) clauses, and extends it to EXISTS and NOT EXISTS clauses. It should result in significantly better planning of EXISTS and NOT EXISTS queries. In general, logically equivalent IN and EXISTS clauses should now have similar performance, whereas previously IN often won.
这 使得 IN(SELECT ...) 子句,以及由此扩展的 EXISTS 和 NOT EXISTS 子句的分析正规化。更有利于规划 EXITS 和 NOT EXISTS 查询。通常来说, IN 和 EXISTS 子句在逻辑上等价。现在它们具有了近似的性能。而过去通常 IN 胜出。
Formerly, a sub-select or view could not be optimized very well if it appeared within the nullable side of an outer join and contained non-strict expressions (for instance, constants) in its result list.
以前,如果外连接可接受空值的那一边是子查询或者视图,并且返回列表里包含不严格的表达式(例如,常量),总是优化的不太好。
This is particularly helpful for long search patterns.
这对于长搜索模式特别有用。
The maximum value was also increased from 1000 to 10000. 最大值也从 1000 提升到 10000。
A new constraint_exclusion setting, partition, was added to specify this behavior.
新的 constraint_exclusion 设置、分化加入到其特定的行为中。
The amount of read-ahead is controlled by effective_io_concurrency. This feature is available only if the kernel has posix_fadvise() support.
预读计数由 effective_io_concurrency 控。这个功能只有内核支持 posix_fadvise() 才能使用。