PGHOSTADDR

PGHOSTADDR is an environment variable used by PostgreSQL client libraries, notably libpq, to specify the host address to connect to. When set, libpq uses the provided address as the destination for the TCP/IP connection and bypasses DNS resolution for the host name given in PGHOST or the connection string. This can improve connection reliability and predictability in environments where DNS is slow, unreliable, or where precise routing is required.

Usage and scope: PGHOSTADDR expects a numeric IP address, either IPv4 (for example 203.0.113.5) or IPv6 (for example 2001:db8::1). The port is still determined separately via PGPORT or the connection string; PGHOSTADDR does not specify the port. PGHOSTADDR applies only to TCP/IP connections and has no effect on Unix-domain socket connections. It is independent of SSL mode and other connection options, except that it fixes the address used for the socket connection.

Behavior in relation to PGHOST: If PGHOST is set to a hostname, setting PGHOSTADDR overrides the DNS resolution of that host, causing the client to connect to the exact IP address provided rather than resolving the host name. This makes the connection less dependent on name resolution and more deterministic in controlled networks.

Security and usage notes: Since environment variables can be read by processes and users with access, exposing IP addresses via PGHOSTADDR should be considered in the context of system security and access control. It is commonly used in scripted deployments, containers, or environments where explicit routing is required.

See also: PGHOST, PGPORT, libpq, psql.