PostgreSQL allows you to set some parameter settings for each session or for each transaction.
You can change the value of a setting during your session, such as the following:
SET work_mem = '16MB';
This value will then be used for every future transaction. You can also change it only for the duration of the "current transaction"
SET LOCAL work_mem = '16MB';
The setting will last until or if you issue the following:
RESET are SQL commands that can be issued from any interface. They apply only to PostgreSQL server parameters, by which we mean parameters that affect the server, but not necessarily the whole server. There may be other parameters, such as JDBC ...