local_preload_libraries — PostgreSQL configuration parameter

This variable specifies one or more shared libraries that are to be preloaded at connection start.

At a glance

What it does

This variable specifies one or more shared libraries that are to be preloaded at connection start. It contains a comma-separated list of library names, where each name is interpreted as for the LOAD command. Whitespace between entries is ignored; surround a library name with double quotes if you need to include whitespace or commas in the name. The parameter value only takes effect at the start of the connection. Subsequent changes have no effect. If a specified library is not found, the connection attempt will fail.

This option can be set by any user. Because of that, the libraries that can be loaded are restricted to those appearing in the plugins subdirectory of the installation’s standard library directory. (It is the database administrator’s responsibility to ensure that only “safe” libraries are installed there.) Entries in local_preload_libraries can specify this directory explicitly, for example $libdir/plugins/mylib, or just specify the library name — mylib would have the same effect as $libdir/plugins/mylib.

(Description quoted from the official PostgreSQL documentation.)

How to apply a change

Can be set per session with SET, per role/database with ALTER ROLE/DATABASE ... SET, or globally in postgresql.conf.

Inspect the current value and source with SHOW local_preload_libraries; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'local_preload_libraries';.

Tuning guidance

This sets a session default (locale, formatting, search path or transaction behaviour) rather than a performance knob. Set it per role or database with ALTER ROLE/DATABASE ... SET so the right default follows the right workload, and prefer setting it explicitly in the application for behaviour the query results depend on.

Reference

PostgreSQL documentation — local_preload_libraries.