20.1. Setting Parameters
20.1.1. Parameter Names and Values
All parameter names are case-insensitive. Every parameter takes a value of one of five types: boolean, string, integer, floating point, or enumerated (enum). The type determines the syntax for setting the parameter:
Boolean: Values can be written as
0(all case-insensitive) or any unambiguous prefix of one of these.
String: In general, enclose the value in single quotes, doubling any single quotes within the value. Quotes can usually be omitted if the value is a simple number or identifier, however. (Values that match an SQL keyword require quoting in some contexts.)
Numeric (integer and floating point): Numeric parameters can be specified in the customary integer and floating-point formats; fractional values are rounded to the nearest integer if the parameter is of integer type. Integer parameters additionally accept hexadecimal input (beginning with
0x) and octal input (beginning with
0), but these formats cannot have a fraction. Do not use thousands separators. Quotes are not required, except for hexadecimal input.
Numeric with Unit: Some numeric parameters have an implicit unit, because they describe quantities of memory or time. The unit might be bytes, kilobytes, blocks (typically eight kilobytes), milliseconds, seconds, or minutes. An unadorned numeric value for one of these settings will use the setting's default unit, which can be learned from
unit. For convenience, settings can be given with a unit specified explicitly, for example
'120 ms'for a time value, and they will be converted to whatever the parameter's actual unit is. Note that the value must be written as a string (with quotes) to use this feature. The unit name is case-sensitive, and there can be whitespace between the numeric value and the unit.
Valid memory units are
TB(terabytes). The multiplier for memory units is 1024, not 1000.
Valid time units are
If a fractional value is specified with a unit, it will be rounded to a multiple of the next smaller unit if there is one. For example,
30.1 GBwill be converted to
32319628902 B. If the parameter is of integer type, a final rounding to integer occurs after any unit conversion.
Enumerated: Enumerated-type parameters are written in the same way as string parameters, but are restricted to have one of a limited set of values. The values allowable for such a parameter can be found from
enumvals. Enum parameter values are case-insensitive.
20.1.2. Parameter Interaction via the Configuration File
The most fundamental way to set these parameters is to edit the file
which is normally kept in the data directory. A default copy is
installed when the database cluster directory is initialized.
An example of what this file might look like is:
# This is a comment log_connections = yes log_destination = 'syslog' search_path = '"$user", public' shared_buffers = 128MB
One parameter is specified per line. The equal sign between name and
value is optional. Whitespace is insignificant (except within a quoted
parameter value) and blank lines are
ignored. Hash marks (
) designate the remainder
of the line as a comment. Parameter values that are not simple
identifiers or numbers must be single-quoted. To embed a single
quote in a parameter value, write either two quotes (preferred)
If the file contains multiple entries for the same parameter,
all but the last one are ignored.
Parameters set in this way provide default values for the cluster. The settings seen by active sessions will be these values unless they are overridden. The following sections describe ways in which the administrator or user can override these defaults.
The configuration file is reread whenever the main server process
signal; this signal is most easily
sent by running
from the command line or by
calling the SQL function
. The main
server process also propagates this signal to all currently running
server processes, so that existing sessions also adopt the new values
(this will happen after they complete any currently-executing client
command). Alternatively, you can
send the signal to a single server process directly. Some parameters
can only be set at server start; any changes to their entries in the
configuration file will be ignored until the server is restarted.
Invalid parameter settings in the configuration file are likewise
ignored (but logged) during
In addition to
data directory contains a file
which has the same format as
is intended to be edited automatically, not manually. This file holds
settings provided through the
This file is read whenever
and its settings take effect in the same way. Settings
External tools may also
. It is not
recommended to do this while the server is running, since a
command could overwrite
such changes. Such tools might simply append new settings to the end,
or they might choose to remove duplicate settings and/or comments
The system view
can be helpful for pre-testing changes to the configuration files, or for
diagnosing problems if a
signal did not have the
20.1.3. Parameter Interaction via SQL
provides three SQL
commands to establish configuration defaults.
provides an SQL-accessible means of changing global defaults; it is
functionally equivalent to editing
In addition, there are two commands that allow setting of defaults
on a per-database or per-role basis:
ALTER DATABASEcommand allows global settings to be overridden on a per-database basis.
ALTER ROLEcommand allows both global and per-database settings to be overridden with user-specific values.
Values set with
are applied only when starting a fresh database session. They
override values obtained from the configuration files or server
command line, and constitute defaults for the rest of the session.
Note that some settings cannot be changed after server start, and
so cannot be set with these commands (or the ones listed below).
Once a client is connected to the database, PostgreSQL provides two additional SQL commands (and equivalent functions) to interact with session-local configuration settings:
SHOWcommand allows inspection of the current value of any parameter. The corresponding SQL function is
current_setting(setting_name text)(see Section 9.27.1 ).
SETcommand allows modification of the current value of those parameters that can be set locally to a session; it has no effect on other sessions. The corresponding SQL function is
set_config(setting_name, new_value, is_local)(see Section 9.27.1 ).
In addition, the system view
used to view and change session-local values:
Querying this view is similar to using
SHOW ALLbut provides more detail. It is also more flexible, since it's possible to specify filter conditions or join against other relations.
UPDATEon this view, specifically updating the
settingcolumn, is the equivalent of issuing
SETcommands. For example, the equivalent of
SET configuration_parameter TO DEFAULT;
UPDATE pg_settings SET setting = reset_val WHERE name = 'configuration_parameter';
20.1.4. Parameter Interaction via the Shell
In addition to setting global defaults or attaching overrides at the database or role level, you can pass settings to PostgreSQL via shell facilities. Both the server and libpq client library accept parameter values via the shell.
During server startup, parameter settings can be passed to the
postgrescommand via the
-ccommand-line parameter. For example,
postgres -c log_connections=yes -c log_destination='syslog'
Settings provided in this way override those set via
ALTER SYSTEM, so they cannot be changed globally without restarting the server.
When starting a client session via libpq , parameter settings can be specified using the
PGOPTIONSenvironment variable. Settings established in this way constitute defaults for the life of the session, but do not affect other sessions. For historical reasons, the format of
PGOPTIONSis similar to that used when launching the
postgrescommand; specifically, the
-cflag must be specified. For example,
env PGOPTIONS="-c geqo=off -c statement_timeout=5min" psql
Other clients and libraries might provide their own mechanisms, via the shell or otherwise, that allow the user to alter session settings without direct use of SQL commands.
20.1.5. Managing Configuration File Contents
provides several features for breaking
files into sub-files.
These features are especially useful when managing multiple servers
with related, but not identical, configurations.
In addition to individual parameter settings,
file can contain
, which specify another file to read and process as if
it were inserted into the configuration file at this point. This
feature allows a configuration file to be divided into physically
separate parts. Include directives simply look like:
If the file name is not an absolute path, it is taken as relative to the directory containing the referencing configuration file. Inclusions can be nested.
There is also an
directive, which acts
the same as the
when the referenced file does not exist or cannot be read. A regular
will consider this an error condition, but
merely logs a message and continues
processing the referencing configuration file.
file can also contain
directives, which specify an entire
directory of configuration files to include. These look like
Non-absolute directory names are taken as relative to the directory
containing the referencing configuration file. Within the specified
directory, only non-directory files whose names end with the
will be included. File names that
start with the
character are also ignored, to
prevent mistakes since such files are hidden on some platforms. Multiple
files within an include directory are processed in file name order
(according to C locale rules, i.e., numbers before letters, and
uppercase letters before lowercase ones).
Include files or directories can be used to logically separate portions
of the database configuration, rather than having a single large
file. Consider a company that has two
database servers, each with a different amount of memory. There are
likely elements of the configuration both will share, for things such
as logging. But memory-related parameters on the server will vary
between the two. And there might be server specific customizations,
too. One way to manage this situation is to break the custom
configuration changes for your site into three files. You could add
this to the end of your
file to include
include 'shared.conf' include 'memory.conf' include 'server.conf'
All systems would have the same
server with a particular amount of memory could share the
; you might have one for all servers
with 8GB of RAM, another for those having 16GB. And
could have truly server-specific
configuration information in it.
Another possibility is to create a configuration file directory and
put this information into files there. For example, a
directory could be referenced at the end of
Then you could name the files in the
00shared.conf 01memory.conf 02server.conf
This naming convention establishes a clear order in which these
files will be loaded. This is important because only the last
setting encountered for a particular parameter while the server is
reading configuration files will be used. In this example,
something set in
would override a
value set in
You might instead use this approach to naming the files descriptively:
00shared.conf 01memory-8GB.conf 02server-foo.conf
This sort of arrangement gives a unique name for each configuration file variation. This can help eliminate ambiguity when several servers have their configurations all stored in one place, such as in a version control repository. (Storing database configuration files under version control is another good practice to consider.)