target_session_attrs

Description

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:

Client library

libpq 18.6

Manual definition

Documented

Source environment fallback

PGTARGETSESSIONATTRS

Compiled fallback expression

DefaultTargetSessionAttrs

Usage

target_session_attrs

Default resolution and service-file precedence

The following environment variables can be used to select default connection parameter values, which will be used by PQconnectdb , PQsetdbLogin and PQsetdb if no value is directly specified by the calling code. These are useful to avoid hard-coding database connection information into simple client applications, for example.

Service names can be defined in either a per-user service file or a system-wide file. If the same service name exists in both the user and the system file, the user file takes precedence. By default, the per-user service file is named ~/.pg_service.conf . On Microsoft Windows, it is named %APPDATA%\postgresql\.pg_service.conf (where %APPDATA% refers to the Application Data subdirectory in the user's profile). A different file name can be specified by setting the environment variable PGSERVICEFILE . The system-wide file is named pg_service.conf . By default it is sought in the etc directory of the PostgreSQL installation (use pg_config --sysconfdir to identify this directory precisely). Another directory, but not a different file name, can be specified by setting the environment variable PGSYSCONFDIR .

Connection parameters obtained from a service file are combined with parameters obtained from other sources. A service file setting overrides the corresponding environment variable, and in turn can be overridden by a value given directly in the connection string. For example, using the above service file, a connection string service=mydb port=5434 will use host somehost , port 5434 , user admin , and other parameters as set by environment variables or built-in defaults.

Environment variable evidence

PGTARGETSESSIONATTRS behaves the same as the target_session_attrs connection parameter.

Related entries

• Connection service file
• Password file
• All libpq environment variables

Documentation and source

• 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

Compare versions

PostgreSQL 13 → 14: changed.

--- 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"

Compares recorded interfaces and attributes. Source fingerprints and build metadata are excluded; an absent sample is not proof of the introduction or removal release.

Related entries

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