blocks|key|160708|text|我不确定这是否正确，从我个人的观点来看，如果在你的应用程序中使用绑定变量，那么PostgreSQL服务器将重用现有的查询计划，而不需要解析，重新编写该计划。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|160709|另一种方法是在应用程序中使用PREPARE语句，当PREPARE语句被执行时，指定的语句将被解析、重写和计划。当随后发出EXECUTE命令时，预准备语句只需为executed.Thus，解析、重写和计划阶段只执行一次，而不是每次执行语句时都执行|160710|有关“准备好的状态网”的更多信息，请查看http://www.postgresql.org/docs/9.0/static/sql-prepare.html|offset|length|160711|entityMap|0|LINK|mutability|MUTABLE|url|http://www.postgresql.org/docs/9.0/static/sql-prepare.html^0|0|0|K|1M|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@$F|S|G|T|1|U]]|A|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

I'm not sure if it is right , from my personal opinion , If use a bind variable in your application, 
then PostgreSQL Server will reuse the esisting query plan without parsed,rewritten the plan again。 

Another way is that use PREPARE statement in your appplication, When the PREPARE statement is executed, 
the specified statement is parsed, rewritten, and planned. When an EXECUTE command is subsequently issued, 
the prepared statement need only be executed.Thus, the parsing, rewriting, and planning stages are only 
performed once, instead of every time the statement is executed

More information about "PREPARED statemnet" please vist 
<a href="http://www.postgresql.org/docs/9.0/static/sql-prepare.html" rel="nofollow">http://www.postgresql.org/docs/9.0/static/sql-prepare.html</a>

blocks|key|1857128|text|我认为postgresql不会缓存这样的计划。当不同的常量传递给查询时，最佳计划可以是不同的。因此，生成新计划要比使用非最优计划更好。如果您需要这样的缓存，您可以使用准备好的语句或pl/pgsql函数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1857129|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I think postgresql doesn't cache such plans. Optimal plans can be different when different constants passed to queries. So it's better to generate new plan than use non-optimal. If you need such cache you may use prepared statements or pl/pgsql functions.

blocks|key|3471599|text|不，除非您显式地告诉服务器使用PREPARE+(或特定于驱动程序的方法)创建预准备语句对象，否则会有缓存。您应该使用预准备语句，因为它们可以为您的应用程序提供开箱即用的SQL注入免疫力。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3471600|您的语句太简单了，即执行时间可能比生成查询计划要长得多。为了获得(已准备好的语句)的优势，您需要-在会话期间多次执行它-查询是复杂的(连接、触发器、函数、规则等)|3471601|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

No, there is caching unless you explicitly tell server to create prepared statement object using PREPARE (or driver specific method). You should use prepared statements because they can give to your application SQL injection immunity out of the box.

You statement is too simple i.e execution time is probably much longer than query plan generation. In order to get an advantage (of prepared statements) you need
- execute it multiple times during your session
- the query is complex (joins, triggers, functions, rules, ...)

blocks|key|3757197|text|Postgres不缓存查询计划。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3757198|命名的预准备语句则是另一回事:如果您注意到经常发出查询，则可以使用Prepare，然后多次执行它。ActiveRecord可能会这么做，我不知道。|3757199|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Postgres DOES NOT cache query plans.

Named prepared statements are a different thing : if you notice a query is often issued, you can use Prepare, and then execute it multiple times. ActiveRecord might do that, I don't know.

I have a Rails/ActiveRecord server utilizing Postgres via the native gem.
I was wondering if/how Postgres reuses query plans.
For example let's say my app has stuff like this:

<pre><code>ActiveRecord::Base.execute("select foo from t where id=5")
ActiveRecord::Base.execute("select foo from t where id=7")
</code></pre>

Will Posgres know that the 2nd SQL is almost identical to the 1st and to reuse existing query plans?

I'm not looking for an answer of "just use models!" or what not; I'm just wondering what happens in the database.

Does Postgres do statement caching on the server?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个Rails/ActiveRecord服务器，通过原生gem利用Postgres。我想知道Postgres是否/如何重用查询计划。例如，假设我的应用程序有这样的内容：ActiveRecord::Base.execute("select foo from t where id=5")ActiveRecord::Ba...

问Postgres在服务器上做语句缓存吗？
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问Postgres在服务器上做语句缓存吗？EN