{"Entry":{"collection":"conn","key":"max-protocol-version","name":"max_protocol_version","aliases":["PGMAXPROTOCOLVERSION","max_protocol_version"],"metadata":{"aliases":["PGMAXPROTOCOLVERSION","max_protocol_version"],"category":"Session and protocol","content_hash":"518281880876a1fdcf00158ba0e62dea5de770297b6015e5067f963d3ff31453","imported_at":"2026-09-30T00:40:34.972986+08:00","name":"max_protocol_version","name_zh":"","slug":"max-protocol-version","summary":"Specifies the protocol version to request from the server. The default is to use version 3.0 of the PostgreSQL protocol, unless the connection string specifies a feature that relies on a higher protocol version, in which case the latest version supported by libpq is used. If the server does not support the protocol version requested by the client, the connection is automatically downgraded to a lower minor protocol version that the server supports. After the connection attempt has completed you can use PQfullProtocolVersion to find out which exact protocol version was negotiated."}},"Definition":{"Collection":"conn","Key":"max-protocol-version","SourceDatabase":"center","Version":"18","SourceTable":"connection_parameter","SourceKey":"max-protocol-version","SourceRevision":"ee8d1a3612338fd9adf250730cb640fcc5233b5491337cc00a316a44e3a0b9f8","Facts":{"comparison_data":{"compiled_default_expression":"NULL","default_evidence":["Specifies the protocol version to request from the server. The default is to use version 3.0 of the PostgreSQL protocol, unless the connection string specifies a feature that relies on a higher protocol version, in which case the latest version supported by libpq is used. If the server does not support the protocol version requested by the client, the connection is automatically downgraded to a lower minor protocol version that the server supports. After the connection attempt has completed you can use PQfullProtocolVersion to find out which exact protocol version was negotiated."],"definition":"Specifies the protocol version to request from the server. The default is to use version 3.0 of the PostgreSQL protocol, unless the connection string specifies a feature that relies on a higher protocol version, in which case the latest version supported by libpq is used. If the server does not support the protocol version requested by the client, the connection is automatically downgraded to a lower minor protocol version that the server supports. After the connection attempt has completed you can use PQfullProtocolVersion to find out which exact protocol version was negotiated. The current supported values are 3.0 , 3.2 , and latest . The latest value is equivalent to the latest protocol version supported by the libpq version being used, which is currently 3.2 .","documented":true,"environment":"PGMAXPROTOCOLVERSION","keyword":"max_protocol_version"},"comparison_hash":"5f247a227834da03d50d6864a46fa9fbd0be14445f495d2c8bfed4a4933ec304","default_evidence":["Specifies the protocol version to request from the server. The default is to use version 3.0 of the PostgreSQL protocol, unless the connection string specifies a feature that relies on a higher protocol version, in which case the latest version supported by libpq is used. If the server does not support the protocol version requested by the client, the connection is automatically downgraded to a lower minor protocol version that the server supports. After the connection attempt has completed you can use PQfullProtocolVersion to find out which exact protocol version was negotiated."],"description":["Specifies the protocol version to request from the server. The default is to use version 3.0 of the PostgreSQL protocol, unless the connection string specifies a feature that relies on a higher protocol version, in which case the latest version supported by libpq is used. If the server does not support the protocol version requested by the client, the connection is automatically downgraded to a lower minor protocol version that the server supports. After the connection attempt has completed you can use PQfullProtocolVersion to find out which exact protocol version was negotiated."],"documented":true,"environment":[{"description":"PGMAXPROTOCOLVERSION behaves the same as the max_protocol_version connection parameter.","name":"PGMAXPROTOCOLVERSION","source_url":"/docs/18/libpq-envars.html"}],"facts":[{"label":"Client library","value":"libpq 18.6"},{"label":"Manual definition","value":"Documented"},{"label":"Source environment fallback","value":"PGMAXPROTOCOLVERSION"},{"label":"Compiled fallback expression","value":"NULL"}],"keyword":"max_protocol_version","manual_html":"\u003cdiv\u003e\u003cdl class=\"variablelist\"\u003e\u003cdt id=\"LIBPQ-CONNECT-MAX-PROTOCOL-VERSION\"\u003e\u003cspan class=\"term\"\u003e\u003ccode class=\"literal\"\u003emax_protocol_version\u003c/code\u003e\u003c/span\u003e \u003c/dt\u003e\u003cdd\u003e\n\u003cp\u003eSpecifies the protocol version to request from the server. The default is to use version \u003ccode class=\"literal\"\u003e3.0\u003c/code\u003e of the \u003cspan class=\"productname\"\u003ePostgreSQL\u003c/span\u003e protocol, unless the connection string specifies a feature that relies on a higher protocol version, in which case the latest version supported by libpq is used. If the server does not support the protocol version requested by the client, the connection is automatically downgraded to a lower minor protocol version that the server supports. After the connection attempt has completed you can use \u003ca class=\"xref\" href=\"/docs/18/libpq-status.html#LIBPQ-PQFULLPROTOCOLVERSION\"\u003e\u003ccode class=\"function\"\u003ePQfullProtocolVersion\u003c/code\u003e\u003c/a\u003e to find out which exact protocol version was negotiated.\u003c/p\u003e\n\u003cp\u003eThe current supported values are \u003ccode class=\"literal\"\u003e3.0\u003c/code\u003e, \u003ccode class=\"literal\"\u003e3.2\u003c/code\u003e, and \u003ccode class=\"literal\"\u003elatest\u003c/code\u003e. The \u003ccode class=\"literal\"\u003elatest\u003c/code\u003e value is equivalent to the latest protocol version supported by the libpq version being used, which is currently \u003ccode class=\"literal\"\u003e3.2\u003c/code\u003e.\u003c/p\u003e\n\u003c/dd\u003e\u003c/dl\u003e\u003c/div\u003e","manual_path":"libpq-connect.html#LIBPQ-CONNECT-MAX-PROTOCOL-VERSION","precedence_evidence":["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."],"related":[{"label":"Connection service file","url":"/docs/18/libpq-pgservice.html"},{"label":"Password file","url":"/docs/18/libpq-pgpass.html"},{"label":"All libpq environment variables","url":"/docs/18/libpq-envars.html"}],"release":{"channel":"stable","evidence_kind":"English manual and source declarations","label":"18.6","major":"18","manifest":{"index":"index.html","major":"18","pages":1148,"pdf":{"A4":{"built_at":"2026-09-26","bytes":15865106,"pages":3154,"sha256":"19512c405da53f9f7fcf0abba359223aa65f021be025bf3411381918f92e3190","url":"/files/documentation/pdf/18/postgresql-18-A4.pdf"},"US":{"built_at":"2026-09-26","bytes":15748059,"pages":3328,"sha256":"facbe6c229e598b872d3d98bef53308f46e06746006fa4590de9a7de9dd46319","url":"/files/documentation/pdf/18/postgresql-18-US.pdf"}},"release":"18.6","source_mode":"en SGML built with pinned official archive","source_sha256":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f","source_url":"https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2","svg_assets":3,"tree":"18"},"ref":"https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2","revision":"ee8d1a3612338fd9adf250730cb640fcc5233b5491337cc00a316a44e3a0b9f8","source_sha256":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"},"sections":[{"paragraphs":["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."],"title":"Default resolution and service-file precedence"},{"paragraphs":["PGMAXPROTOCOLVERSION behaves the same as the max_protocol_version connection parameter."],"title":"Environment variable evidence"}],"signature":"max_protocol_version","source_option":{"compiled_default_expression":"NULL","declaration":"\"max_protocol_version\", \"PGMAXPROTOCOLVERSION\", NULL, NULL, \"Max-Protocol-Version\", \"\", 6, offsetof(struct pg_conn, max_protocol_version)","environment":"PGMAXPROTOCOLVERSION","keyword":"max_protocol_version","source_notes":[]},"sources":[{"anchor":"LIBPQ-CONNECT-MAX-PROTOCOL-VERSION","file":"libpq-connect.html","label":"18.6 English manual · libpq-connect.html","sha256":"c26a7fc3dcda6066cfe540641ae2690faf3d3c03277f30b4dfc2328ab45c212f","url":"/docs/18/libpq-connect.html#LIBPQ-CONNECT-MAX-PROTOCOL-VERSION"},{"archive_sha256":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f","file":"src/interfaces/libpq/fe-connect.c","label":"18.6 libpq connection option declarations","sha256":"44a6e386cbfd67ebe768d6ef5493098119c2e6b4796239d53e5ed7b122b206a5","url":"https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2"},{"anchor":"","file":"libpq-envars.html","label":"18.6 English manual · libpq-envars.html","sha256":"d64db73f3d48127bb984a5f775e77b7bcca2ba4bd218333cf24a45fcdd7c4363","url":"/docs/18/libpq-envars.html"},{"anchor":"","file":"libpq-pgservice.html","label":"18.6 English manual · libpq-pgservice.html","sha256":"6035a3f0ee1d0fd80db5bf58834390b884eecd23206659bdf6f07560deea5aa7","url":"/docs/18/libpq-pgservice.html"}],"tables":[{"columns":[{"key":"name","label":"Variable"},{"key":"description","label":"Documented behavior"}],"key":"environment","rows":[{"description":"PGMAXPROTOCOLVERSION behaves the same as the max_protocol_version connection parameter.","name":{"text":"PGMAXPROTOCOLVERSION","url":"/docs/18/libpq-envars.html"}}],"title":"Environment fallback"}]},"ManualEvidence":{"manual_path":"libpq-connect.html#LIBPQ-CONNECT-MAX-PROTOCOL-VERSION","release":{"channel":"stable","evidence_kind":"English manual and source declarations","label":"18.6","major":"18","manifest":{"index":"index.html","major":"18","pages":1148,"pdf":{"A4":{"built_at":"2026-09-26","bytes":15865106,"pages":3154,"sha256":"19512c405da53f9f7fcf0abba359223aa65f021be025bf3411381918f92e3190","url":"/files/documentation/pdf/18/postgresql-18-A4.pdf"},"US":{"built_at":"2026-09-26","bytes":15748059,"pages":3328,"sha256":"facbe6c229e598b872d3d98bef53308f46e06746006fa4590de9a7de9dd46319","url":"/files/documentation/pdf/18/postgresql-18-US.pdf"}},"release":"18.6","source_mode":"en SGML built with pinned official archive","source_sha256":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f","source_url":"https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2","svg_assets":3,"tree":"18"},"ref":"https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2","revision":"ee8d1a3612338fd9adf250730cb640fcc5233b5491337cc00a316a44e3a0b9f8","source_sha256":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f"},"sources":[{"anchor":"LIBPQ-CONNECT-MAX-PROTOCOL-VERSION","file":"libpq-connect.html","label":"18.6 English manual · libpq-connect.html","sha256":"c26a7fc3dcda6066cfe540641ae2690faf3d3c03277f30b4dfc2328ab45c212f","url":"/docs/18/libpq-connect.html#LIBPQ-CONNECT-MAX-PROTOCOL-VERSION"},{"archive_sha256":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f","file":"src/interfaces/libpq/fe-connect.c","label":"18.6 libpq connection option declarations","sha256":"44a6e386cbfd67ebe768d6ef5493098119c2e6b4796239d53e5ed7b122b206a5","url":"https://ftp.postgresql.org/pub/source/v18.6/postgresql-18.6.tar.bz2"},{"anchor":"","file":"libpq-envars.html","label":"18.6 English manual · libpq-envars.html","sha256":"d64db73f3d48127bb984a5f775e77b7bcca2ba4bd218333cf24a45fcdd7c4363","url":"/docs/18/libpq-envars.html"},{"anchor":"","file":"libpq-pgservice.html","label":"18.6 English manual · libpq-pgservice.html","sha256":"6035a3f0ee1d0fd80db5bf58834390b884eecd23206659bdf6f07560deea5aa7","url":"/docs/18/libpq-pgservice.html"}]},"MeasuredEvidence":{}},"Text":{"Collection":"conn","Key":"max-protocol-version","SourceDatabase":"center","Version":"18","Locale":"en","Title":"max_protocol_version","Summary":"Specifies the protocol version to request from the server. The default is to use version 3.0 of the PostgreSQL protocol, unless the connection string specifies a feature that relies on a higher protocol version, in which case the latest version supported by libpq is used. If the server does not support the protocol version requested by the client, the connection is automatically downgraded to a lower minor protocol version that the server supports. After the connection attempt has completed you can use PQfullProtocolVersion to find out which exact protocol version was negotiated.","BodyHTML":"\u003cdiv\u003e\u003cdl\u003e\u003cdt id=\"LIBPQ-CONNECT-MAX-PROTOCOL-VERSION\"\u003e\u003cspan\u003e\u003ccode\u003emax_protocol_version\u003c/code\u003e\u003c/span\u003e \u003c/dt\u003e\u003cdd\u003e\n\u003cp\u003eSpecifies the protocol version to request from the server. The default is to use version \u003ccode\u003e3.0\u003c/code\u003e of the \u003cspan\u003ePostgreSQL\u003c/span\u003e protocol, unless the connection string specifies a feature that relies on a higher protocol version, in which case the latest version supported by libpq is used. If the server does not support the protocol version requested by the client, the connection is automatically downgraded to a lower minor protocol version that the server supports. After the connection attempt has completed you can use \u003ca href=\"/docs/18/libpq-status.html#LIBPQ-PQFULLPROTOCOLVERSION\" rel=\"nofollow\"\u003e\u003ccode\u003ePQfullProtocolVersion\u003c/code\u003e\u003c/a\u003e to find out which exact protocol version was negotiated.\u003c/p\u003e\n\u003cp\u003eThe current supported values are \u003ccode\u003e3.0\u003c/code\u003e, \u003ccode\u003e3.2\u003c/code\u003e, and \u003ccode\u003elatest\u003c/code\u003e. The \u003ccode\u003elatest\u003c/code\u003e value is equivalent to the latest protocol version supported by the libpq version being used, which is currently \u003ccode\u003e3.2\u003c/code\u003e.\u003c/p\u003e\n\u003c/dd\u003e\u003c/dl\u003e\u003c/div\u003e","SourceRevision":"ee8d1a3612338fd9adf250730cb640fcc5233b5491337cc00a316a44e3a0b9f8","ContentHash":"4216ac545392974fe9f8d9716243ae2c716e58695482b14c81f80c2d3f86fc15","Payload":{"description":["Specifies the protocol version to request from the server. The default is to use version 3.0 of the PostgreSQL protocol, unless the connection string specifies a feature that relies on a higher protocol version, in which case the latest version supported by libpq is used. If the server does not support the protocol version requested by the client, the connection is automatically downgraded to a lower minor protocol version that the server supports. After the connection attempt has completed you can use PQfullProtocolVersion to find out which exact protocol version was negotiated."],"manual_html":"\u003cdiv\u003e\u003cdl class=\"variablelist\"\u003e\u003cdt id=\"LIBPQ-CONNECT-MAX-PROTOCOL-VERSION\"\u003e\u003cspan class=\"term\"\u003e\u003ccode class=\"literal\"\u003emax_protocol_version\u003c/code\u003e\u003c/span\u003e \u003c/dt\u003e\u003cdd\u003e\n\u003cp\u003eSpecifies the protocol version to request from the server. The default is to use version \u003ccode class=\"literal\"\u003e3.0\u003c/code\u003e of the \u003cspan class=\"productname\"\u003ePostgreSQL\u003c/span\u003e protocol, unless the connection string specifies a feature that relies on a higher protocol version, in which case the latest version supported by libpq is used. If the server does not support the protocol version requested by the client, the connection is automatically downgraded to a lower minor protocol version that the server supports. After the connection attempt has completed you can use \u003ca class=\"xref\" href=\"/docs/18/libpq-status.html#LIBPQ-PQFULLPROTOCOLVERSION\"\u003e\u003ccode class=\"function\"\u003ePQfullProtocolVersion\u003c/code\u003e\u003c/a\u003e to find out which exact protocol version was negotiated.\u003c/p\u003e\n\u003cp\u003eThe current supported values are \u003ccode class=\"literal\"\u003e3.0\u003c/code\u003e, \u003ccode class=\"literal\"\u003e3.2\u003c/code\u003e, and \u003ccode class=\"literal\"\u003elatest\u003c/code\u003e. The \u003ccode class=\"literal\"\u003elatest\u003c/code\u003e value is equivalent to the latest protocol version supported by the libpq version being used, which is currently \u003ccode class=\"literal\"\u003e3.2\u003c/code\u003e.\u003c/p\u003e\n\u003c/dd\u003e\u003c/dl\u003e\u003c/div\u003e","related":[{"label":"Connection service file","url":"/docs/18/libpq-pgservice.html"},{"label":"Password file","url":"/docs/18/libpq-pgpass.html"},{"label":"All libpq environment variables","url":"/docs/18/libpq-envars.html"}],"sections":[{"paragraphs":["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."],"title":"Default resolution and service-file precedence"},{"paragraphs":["PGMAXPROTOCOLVERSION behaves the same as the max_protocol_version connection parameter."],"title":"Environment variable evidence"}],"tables":[{"columns":[{"key":"name","label":"Variable"},{"key":"description","label":"Documented behavior"}],"key":"environment","rows":[{"description":"PGMAXPROTOCOLVERSION behaves the same as the max_protocol_version connection parameter.","name":{"text":"PGMAXPROTOCOLVERSION","url":"/docs/18/libpq-envars.html"}}],"title":"Environment fallback"}]}},"RequestedLocale":"zh-Hans","Fallback":true,"Versions":["18","19","20"],"Locales":["en"],"Signatures":null,"Spellings":null,"SQLState":null,"Evidence":null}