查询一个参数（postgresql.conf 设置），比如“max_connections”
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Query a parameter (postgresql.conf setting) like "max_connections"
提问by Greg Kramida
Does anyone know if it's even possible (and how, if yes) to query a database server setting in PostgreSQL (9.1)?
有谁知道是否有可能（以及如何，如果有）在 PostgreSQL (9.1) 中查询数据库服务器设置？
I need to check the max_connections(maximum number of open db connections) setting.
我需要检查max_connections（打开数据库连接的最大数量）设置。
回答by Erwin Brandstetter
Can be as simple as:
可以很简单：
SHOW max_connections;
This returns the currently effective setting. Be aware that it can differ from the setting in postgresql.confas there are a couple of ways to set run-time parameters in PostgreSQL. To reset the "original" setting from postgresql.confin your current session:
这将返回当前有效的设置。请注意，它可能与 中的设置不同，postgresql.conf因为有几种方法可以在 PostgreSQL 中设置运行时参数。从postgresql.conf当前会话中重置“原始”设置：
RESET max_connections;
However, not applicable to this particular setting. Per documentation:
但是，不适用于此特定设置。根据文档：
This parameter can only be set at server start.
该参数只能在服务器启动时设置。
To see allsettings:
查看所有设置：
SHOW ALL;
More on the SHOWcommand in the manual.
If you need more details or want to integrate the look-up into a standard SELECTquery, there is also:
更多关于SHOW手册中的命令。
如果您需要更多详细信息或希望将查找集成到标准SELECT查询中，还有：
SELECT * FROM pg_settings;
Returns the same result as SHOW ALL, but with additional information per setting. For your original request:
返回与 相同的结果SHOW ALL，但每个设置都有附加信息。对于您的原始请求：
SELECT *
FROM pg_settings
WHERE name = 'max_connections';
There is also the functional equivalent current_setting(), which can be nested in DML statements.
还有功能等效的current_setting()，它可以嵌套在 DML 语句中。
SELECT current_setting('max_connections');
Related:
有关的：
