target_session_attrs

说明

决定会话必须具备哪些属性才能被接受。通常与多个主机名一起使用，从多台主机中选择第一个符合条件的连接。共有六种模式：

客户端库

libpq 18.6

手册定义

手册已记载

源码中的环境变量回退

PGTARGETSESSIONATTRS

编译时回退表达式

DefaultTargetSessionAttrs

用法

target_session_attrs

默认值解析与服务文件优先级

以下环境变量可用于选择连接参数的默认值，供 PQconnectdb 、 PQsetdbLogin 和 PQsetdb 在调用代码未直接指定参数值时使用。例如，这样可以避免在简单的客户端应用程序中硬编码数据库连接信息。

服务名称可以在每个用户的服务文件或系统范围的文件中定义。如果同一个服务名称存在于用户文件和系统文件中，则用户文件优先。默认情况下，每个用户的服务文件名为 ~/.pg_service.conf 。在Microsoft Windows上，它的名称为 %APPDATA%\postgresql\.pg_service.conf （其中 %APPDATA% 指用户配置文件夹中的应用数据子目录）。可以通过设置环境变量 PGSERVICEFILE 来指定不同的文件名。系统范围的文件名为 pg_service.conf 。默认情况下，在 PostgreSQL 安装的 etc 目录中寻找（使用 pg_config --sysconfdir 来准确识别此目录）。可以通过设置环境变量 PGSYSCONFDIR 来指定另一个目录，但不能指定不同的文件名。

从服务文件中获取的连接参数会与其他来源的参数合并。服务文件中的设置会覆盖相应的环境变量，而连接字符串中直接给出的值又会覆盖服务文件中的设置。例如，使用上述服务文件时，连接字符串 service=mydb port=5434 将使用主机 somehost 、端口 5434 、用户 admin ，以及由环境变量或内置默认值设置的其他参数。

环境变量证据

PGTARGETSESSIONATTRS 的行为与 target_session_attrs 连接参数相同。

相关条目

• 连接服务文件
• 口令文件
• 所有 libpq 环境变量

文档与源码

• 18.6 English manual · libpq-connect.html
• 18.6 libpq connection option declarations
• 18.6 English manual · libpq-envars.html
• 18.6 English manual · libpq-pgservice.html

版本比较

PostgreSQL 13 → 14: 属性变化。

以下差异保留原始字段名与英文源描述。

--- PostgreSQL 13
+++ PostgreSQL 14
@@ -1,9 +1,10 @@
 {
   "compiled_default_expression": "DefaultTargetSessionAttrs",
   "default_evidence": [
-    "If this parameter is set to read-write , only a connection in which read-write transactions are accepted by default is considered acceptable. The query SHOW transaction_read_only will be sent upon any successful connection; if it returns on , the connection will be closed. If multiple hosts were specified in the connection string, any remaining servers will be tried just as if the connection attempt had failed. The default value of this parameter, any , regards all connections as acceptable."
+    "session must accept read-write transactions by default (that is, the server must not be in hot standby mode and the default_transaction_read_only parameter must be off )",
+    "session must not accept read-write transactions by default (the converse)"
   ],
-  "definition": "If this parameter is set to read-write , only a connection in which read-write transactions are accepted by default is considered acceptable. The query SHOW transaction_read_only will be sent upon any successful connection; if it returns on , the connection will be closed. If multiple hosts were specified in the connection string, any remaining servers will be tried just as if the connection attempt had failed. The default value of this parameter, any , regards all connections as acceptable.",
+  "definition": "This option determines whether the session must have certain properties to be acceptable. It's typically used in combination with multiple host names to select the first acceptable alternative among several hosts. There are six modes: any (default) any successful connection is acceptable read-write session must accept read-write transactions by default (that is, the server must not be in hot standby mode and the default_transaction_read_only parameter must be off ) read-only session must not accept read-write transactions by default (the converse) primary server must not be in hot standby mode standby server must be in hot standby mode prefer-standby first try to find a standby server, but if none of the listed hosts is a standby server, try again in any mode",
   "documented": true,
   "environment": "PGTARGETSESSIONATTRS",
   "keyword": "target_session_attrs"

比较已记录的接口与属性，排除来源指纹和构建元数据。某个样本中没有记录，不能据此判断实际引入或移除的版本。

相关条目

• dbname
• host
• hostaddr
• load_balance_hosts
• port
• service