load_balance_hosts

说明

控制客户端尝试连接可用主机和地址的顺序。一旦某次连接尝试成功，就不会再尝试其他主机和地址。该参数通常与多个主机名或返回多个 IP 地址的 DNS 记录一起使用。它还可以与 target_session_attrs 组合使用，例如只在备库之间进行负载均衡。连接一旦成功建立，随后在返回的连接上发出的所有查询都会发送到同一台服务器。目前有两种模式：

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

PGLOADBALANCEHOSTS

编译时回退表达式

DefaultLoadBalanceHosts

用法

load_balance_hosts

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

PGLOADBALANCEHOSTS 的行为与 load_balance_hosts 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 15 → 16: 新增收录。

以下差异保留原始字段名与英文源描述。

--- PostgreSQL 15
+++ PostgreSQL 16
@@ -1 +1,8 @@
-该版未收录
+{
+  "compiled_default_expression": "DefaultLoadBalanceHosts",
+  "default_evidence": [],
+  "definition": "Controls the order in which the client tries to connect to the available hosts and addresses. Once a connection attempt is successful no other hosts and addresses will be tried. This parameter is typically used in combination with multiple host names or a DNS record that returns multiple IPs. This parameter can be used in combination with target_session_attrs to, for example, load balance over standby servers only. Once successfully connected, subsequent queries on the returned connection will all be sent to the same server. There are currently two modes: disable (default) No load balancing across hosts is performed. Hosts are tried in the order in which they are provided and addresses are tried in the order they are received from DNS or a hosts file. random Hosts and addresses are tried in random order. This value is mostly useful when opening multiple connections at the same time, possibly from different machines. This way connections can be load balanced across multiple PostgreSQL servers. While random load balancing, due to its random nature, will almost never result in a completely uniform distribution, it statistically gets quite close. One important aspect here is that this algorithm uses two levels of random choices: First the hosts will be resolved in random order. Then secondly, before resolving the next host, all resolved addresses for the current host will be tried in random order. This behaviour can skew the amount of connections each node gets greatly in certain cases, for instance when some hosts resolve to more addresses than others. But such a skew can also be used on purpose, e.g. to increase the number of connections a larger server gets by providing its hostname multiple times in the host string. When using this value it's recommended to also configure a reasonable value for connect_timeout . Because then, if one of the nodes that are used for load balancing is not responding, a new node will be tried.",
+  "documented": true,
+  "environment": "PGLOADBALANCEHOSTS",
+  "keyword": "load_balance_hosts"
+}

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
• port
• service
• target_session_attrs