RESET restores run-time parameters to their default values. RESET is an alternative spelling for
SET configuration_parameter TO DEFAULT
Refer to SET for details.
The default value is defined as the value that the parameter would have had, if no SET had ever been issued for it in the current session. The actual source of this value might be a compiled-in default, the configuration file, command-line options, or per-database or per-user default settings. This is subtly different from defining it as "the value that the parameter had at session start", because if the value came from the configuration file, it will be reset to whatever is specified by the configuration file now. See Chapter 18 for details.
The transactional behavior of RESET is the same as SET: its effects will be undone by transaction rollback.