'\" t
.\"     Title: ALTER SYSTEM
.\"    Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets v1.75.2 <http://docbook.sf.net/>
.\"      Date: 2016
.\"    Manual: PostgreSQL 9.5.2 Documentation
.\"    Source: PostgreSQL 9.5.2
.\"  Language: English
.\"
.TH "ALTER SYSTEM" "5sql" "2016" "PostgreSQL 9.5.2" "PostgreSQL 9.5.2 Documentation"
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.SH "NAME"
ALTER_SYSTEM \- change a server configuration parameter
.SH "SYNOPSIS"
.sp
.nf
ALTER SYSTEM SET \fIconfiguration_parameter\fR { TO | = } { \fIvalue\fR | \(aq\fIvalue\fR\(aq | DEFAULT }

ALTER SYSTEM RESET \fIconfiguration_parameter\fR
ALTER SYSTEM RESET ALL
.fi
.SH "DESCRIPTION"
.PP

\fBALTER SYSTEM\fR
is used for changing server configuration parameters across the entire database cluster\&. It can be more convenient than the traditional method of manually editing the
postgresql\&.conf
file\&.
\fBALTER SYSTEM\fR
writes the given parameter setting to the
postgresql\&.auto\&.conf
file, which is read in addition to
postgresql\&.conf\&. Setting a parameter to
DEFAULT, or using the
\fBRESET\fR
variant, removes that configuration entry from the
postgresql\&.auto\&.conf
file\&. Use
RESET ALL
to remove all such configuration entries\&.
.PP
Values set with
\fBALTER SYSTEM\fR
will be effective after the next server configuration reload (SIGHUP
or
pg_ctl reload), or after the next server restart in the case of parameters that can only be changed at server start\&.
.PP
Only superusers can use
\fBALTER SYSTEM\fR\&. Also, since this command acts directly on the file system and cannot be rolled back, it is not allowed inside a transaction block or function\&.
.SH "PARAMETERS"
.PP
\fIconfiguration_parameter\fR
.RS 4
Name of a settable configuration parameter\&. Available parameters are documented in
Chapter 18, Server Configuration, in the documentation\&.
.RE
.PP
\fIvalue\fR
.RS 4
New value of the parameter\&. Values can be specified as string constants, identifiers, numbers, or comma\-separated lists of these, as appropriate for the particular parameter\&.
DEFAULT
can be written to specify removing the parameter and its value from
postgresql\&.auto\&.conf\&.
.RE
.SH "NOTES"
.PP
This command can\(aqt be used to set
data_directory, nor parameters that are not allowed in
postgresql\&.conf
(e\&.g\&.,
preset options)\&.
.PP
See
Section 18.1, \(lqSetting Parameters\(rq, in the documentation
for other ways to set the parameters\&.
.SH "EXAMPLES"
.PP
Set the
wal_level:
.sp
.if n \{\
.RS 4
.\}
.nf
ALTER SYSTEM SET wal_level = hot_standby;
.fi
.if n \{\
.RE
.\}
.PP
Undo that, restoring whatever setting was effective in
postgresql\&.conf:
.sp
.if n \{\
.RS 4
.\}
.nf
ALTER SYSTEM RESET wal_level;
.fi
.if n \{\
.RE
.\}
.sp
.SH "COMPATIBILITY"
.PP
The
\fBALTER SYSTEM\fR
statement is a
PostgreSQL
extension\&.
.SH "SEE ALSO"
\fBSET\fR(5), \fBSHOW\fR(5)