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48.67. pg_settings

The view pg_settings provides access to run-time parameters of the server. It is essentially an alternative interface to the SHOW and SET commands. It also provides access to some facts about each parameter that are not directly available from SHOW, such as minimum and maximum values.

Table 48-68. pg_settings Columns

Name Type Description
name text Run-time configuration parameter name
setting text Current value of the parameter
unit text Implicit unit of the parameter
category text Logical group of the parameter
short_desc text A brief description of the parameter
extra_desc text Additional, more detailed, description of the parameter
context text Context required to set the parameter's value (see below)
vartype text Parameter type (bool, enum, integer, real, or string)
source text Source of the current parameter value
min_val text Minimum allowed value of the parameter (null for non-numeric values)
max_val text Maximum allowed value of the parameter (null for non-numeric values)
enumvals text[] Allowed values of an enum parameter (null for non-enum values)
boot_val text Parameter value assumed at server startup if the parameter is not otherwise set
reset_val text Value that RESET would reset the parameter to in the current session
sourcefile text Configuration file the current value was set in (null for values set from sources other than configuration files, or when examined by a non-superuser); helpful when using include directives in configuration files
sourceline integer Line number within the configuration file the current value was set at (null for values set from sources other than configuration files, or when examined by a non-superuser)

There are several possible values of context. In order of decreasing difficulty of changing the setting, they are:

internal

These settings cannot be changed directly; they reflect internally determined values. Some of them may be adjustable by rebuilding the server with different configuration options, or by changing options supplied to initdb.

postmaster

These settings can only be applied when the server starts, so any change requires restarting the server. Values for these settings are typically stored in the postgresql.conf file, or passed on the command line when starting the server. Of course, settings with any of the lower context types can also be set at server start time.

sighup

Changes to these settings can be made in postgresql.conf without restarting the server. Send a SIGHUP signal to the postmaster to cause it to re-read postgresql.conf and apply the changes. The postmaster will also forward the SIGHUP signal to its child processes so that they all pick up the new value.

backend

Changes to these settings can be made in postgresql.conf without restarting the server; they can also be set for a particular session in the connection request packet (for example, via libpq's PGOPTIONS environment variable). However, these settings never change in a session after it is started. If you change them in postgresql.conf, send a SIGHUP signal to the postmaster to cause it to re-read postgresql.conf. The new values will only affect subsequently-launched sessions.

superuser

These settings can be set from postgresql.conf, or within a session via the SET command; but only superusers can change them via SET. Changes in postgresql.conf will affect existing sessions only if no session-local value has been established with SET.

user

These settings can be set from postgresql.conf, or within a session via the SET command. Any user is allowed to change his session-local value. Changes in postgresql.conf will affect existing sessions only if no session-local value has been established with SET.

See Section 18.1 for more information about the various ways to change these parameters.

The pg_settings view cannot be inserted into or deleted from, but it can be updated. An UPDATE applied to a row of pg_settings is equivalent to executing the SET command on that named parameter. The change only affects the value used by the current session. If an UPDATE is issued within a transaction that is later aborted, the effects of the UPDATE command disappear when the transaction is rolled back. Once the surrounding transaction is committed, the effects will persist until the end of the session, unless overridden by another UPDATE or SET.

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