18.10. Client Connection Defaults

This variable specifies the order in which schemas are searched when an object (table, data type, function, etc.) is referenced by a simple name with no schema component. When there are objects of identical names in different schemas, the one found first in the search path is used. An object that is not in any of the schemas in the search path can only be referenced by specifying its containing schema with a qualified (dotted) name.

The value for search_path has to be a comma-separated list of schema names. If one of the list items is the special value $user, then the schema having the name returned by SESSION_USER is substituted, if there is such a schema. (If not, $user is ignored.)

The system catalog schema, pg_catalog, is always searched, whether it is mentioned in the path or not. If it is mentioned in the path then it will be searched in the specified order. If pg_catalog is not in the path then it will be searched before searching any of the path items.

Likewise, the current session's temporary-table schema, pg_temp_nnn, is always searched if it exists. It can be explicitly listed in the path by using the alias pg_temp. If it is not listed in the path then it is searched first (before even pg_catalog). However, the temporary schema is only searched for relation (table, view, sequence, etc) and data type names. It will never be searched for function or operator names.

When objects are created without specifying a particular target schema, they will be placed in the first schema listed in the search path. An error is reported if the search path is empty.

The default value for this parameter is '"$user", public' (where the second part will be ignored if there is no schema named public). This supports shared use of a database (where no users have private schemas, and all share use of public), private per-user schemas, and combinations of these. Other effects can be obtained by altering the default search path setting, either globally or per-user.

The current effective value of the search path can be examined via the SQL function current_schemas(). This is not quite the same as examining the value of search_path, since current_schemas() shows how the requests appearing in search_path were resolved.

For more information on schema handling, see Section 5.7.

This variable specifies the default tablespace in which to create objects (tables and indexes) when a CREATE command does not explicitly specify a tablespace.

The value is either the name of a tablespace, or an empty string to specify using the default tablespace of the current database. If the value does not match the name of any existing tablespace, PostgreSQL will automatically use the default tablespace of the current database. If a nondefault tablespace is specified, the user must have CREATE privilege for it, or creation attempts will fail.

This variable is not used for temporary tables; for them, temp_tablespaces is consulted instead.

For more information on tablespaces, see Section 21.6.

This variable specifies tablespace(s) in which to create temporary objects (temp tables and indexes on temp tables) when a CREATE command does not explicitly specify a tablespace. Temporary files for purposes such as sorting large data sets are also created in these tablespace(s).

The value is a list of names of tablespaces. When there is more than one name in the list, PostgreSQL chooses a random member of the list each time a temporary object is to be created; except that within a transaction, successively created temporary objects are placed in successive tablespaces from the list. If the selected element of the list is an empty string, PostgreSQL will automatically use the default tablespace of the current database instead.

When temp_tablespaces is set interactively, specifying a nonexistent tablespace is an error, as is specifying a tablespace for which the user does not have CREATE privilege. However, when using a previously set value, nonexistent tablespaces are ignored, as are tablespaces for which the user lacks CREATE privilege. In particular, this rule applies when using a value set in postgresql.conf.

The default value is an empty string, which results in all temporary objects being created in the default tablespace of the current database.

See also default_tablespace.

This parameter is normally on. When set to off, it disables validation of the function body string during CREATE FUNCTION. Disabling validation is occasionally useful to avoid problems such as forward references when restoring function definitions from a dump.

Each SQL transaction has an isolation level, which can be either "read uncommitted", "read committed", "repeatable read", or "serializable". This parameter controls the default isolation level of each new transaction. The default is "read committed".

Consult Chapter 13 and SET TRANSACTION for more information.

A read-only SQL transaction cannot alter non-temporary tables. This parameter controls the default read-only status of each new transaction. The default is off (read/write).

Consult SET TRANSACTION for more information.

Controls firing of replication-related triggers and rules for the current session. Setting this variable requires superuser privilege and results in discarding any previously cached query plans. Possible values are origin (the default), replica and local. See ALTER TABLE for more information.

Abort any statement that takes over the specified number of milliseconds, starting from the time the command arrives at the server from the client. If log_min_error_statement is set to ERROR or lower, the statement that timed out will also be logged. A value of zero (the default) turns off the limitation.

Setting statement_timeout in postgresql.conf is not recommended because it affects all sessions.

VACUUM performs a whole-table scan if the table's pg_class.relfrozenxid field has reached the age specified by this setting. The default is 150 million transactions. Although users can set this value anywhere from zero to one billion, VACUUM will silently limit the effective value to 95% of autovacuum_freeze_max_age, so that a periodical manual VACUUM has a chance to run before an anti-wraparound autovacuum is launched for the table. For more information see Section 23.1.4.

Specifies the cutoff age (in transactions) that VACUUM should use to decide whether to replace transaction IDs with FrozenXID while scanning a table. The default is 50 million transactions. Although users can set this value anywhere from zero to one billion, VACUUM will silently limit the effective value to half the value of autovacuum_freeze_max_age, so that there is not an unreasonably short time between forced autovacuums. For more information see Section 23.1.4.

Sets how binary values are to be encoded in XML. This applies for example when bytea values are converted to XML by the functions xmlelement or xmlforest. Possible values are base64 and hex, which are both defined in the XML Schema standard. The default is base64. For further information about XML-related functions, see Section 9.14.

The actual choice here is mostly a matter of taste, constrained only by possible restrictions in client applications. Both methods support all possible values, although the hex encoding will be somewhat larger than the base64 encoding.

Sets whether DOCUMENT or CONTENT is implicit when converting between XML and character string values. See Section 8.13 for a description of this. Valid values are DOCUMENT and CONTENT. The default is CONTENT.

According to the SQL standard, the command to set this option is

SET XML OPTION { DOCUMENT | CONTENT };

This syntax is also available in PostgreSQL.

Sets the display format for date and time values, as well as the rules for interpreting ambiguous date input values. For historical reasons, this variable contains two independent components: the output format specification (ISO, Postgres, SQL, or German) and the input/output specification for year/month/day ordering (DMY, MDY, or YMD). These can be set separately or together. The keywords Euro and European are synonyms for DMY; the keywords US, NonEuro, and NonEuropean are synonyms for MDY. See Section 8.5 for more information. The built-in default is ISO, MDY, but initdb will initialize the configuration file with a setting that corresponds to the behavior of the chosen lc_time locale.

Sets the display format for interval values. The value sql_standard will produce output matching SQL standard interval literals. The value postgres (which is the default) will produce output matching PostgreSQL releases prior to 8.4 when the DateStyle parameter was set to ISO. The value postgres_verbose will produce output matching PostgreSQL releases prior to 8.4 when the DateStyle parameter was set to non-ISO output. The value iso_8601 will produce output matching the time interval "format with designators" defined in section 4.4.3.2 of ISO 8601.

The IntervalStyle parameter also affects the interpretation of ambiguous interval input. See Section 8.5.4 for more information.

Sets the time zone for displaying and interpreting time stamps. The default is unknown, which means to use whatever the system environment specifies as the time zone. See Section 8.5.3 for more information.

Sets the collection of time zone abbreviations that will be accepted by the server for datetime input. The default is 'Default', which is a collection that works in most of the world; there are also 'Australia' and 'India', and other collections can be defined for a particular installation. See Appendix B for more information.

This parameter adjusts the number of digits displayed for floating-point values, including float4, float8, and geometric data types. The parameter value is added to the standard number of digits (FLT_DIG or DBL_DIG as appropriate). The value can be set as high as 2, to include partially-significant digits; this is especially useful for dumping float data that needs to be restored exactly. Or it can be set negative to suppress unwanted digits.

Sets the client-side encoding (character set). The default is to use the database encoding.

Sets the language in which messages are displayed. Acceptable values are system-dependent; see Section 22.1 for more information. If this variable is set to the empty string (which is the default) then the value is inherited from the execution environment of the server in a system-dependent way.

On some systems, this locale category does not exist. Setting this variable will still work, but there will be no effect. Also, there is a chance that no translated messages for the desired language exist. In that case you will continue to see the English messages.

Only superusers can change this setting, because it affects the messages sent to the server log as well as to the client.

Sets the locale to use for formatting monetary amounts, for example with the to_char family of functions. Acceptable values are system-dependent; see Section 22.1 for more information. If this variable is set to the empty string (which is the default) then the value is inherited from the execution environment of the server in a system-dependent way.

Sets the locale to use for formatting numbers, for example with the to_char family of functions. Acceptable values are system-dependent; see Section 22.1 for more information. If this variable is set to the empty string (which is the default) then the value is inherited from the execution environment of the server in a system-dependent way.

Sets the locale to use for formatting dates and times, for example with the to_char family of functions. Acceptable values are system-dependent; see Section 22.1 for more information. If this variable is set to the empty string (which is the default) then the value is inherited from the execution environment of the server in a system-dependent way.

Selects the text search configuration that is used by those variants of the text search functions that do not have an explicit argument specifying the configuration. See Chapter 12 for further information. The built-in default is pg_catalog.simple, but initdb will initialize the configuration file with a setting that corresponds to the chosen lc_ctype locale, if a configuration matching that locale can be identified.

If a dynamically loadable module needs to be opened and the file name specified in the CREATE FUNCTION or LOAD command does not have a directory component (i.e., the name does not contain a slash), the system will search this path for the required file.

The value for dynamic_library_path has to be a list of absolute directory paths separated by colons (or semi-colons on Windows). If a list element starts with the special string $libdir, the compiled-in PostgreSQL package library directory is substituted for $libdir. This is where the modules provided by the standard PostgreSQL distribution are installed. (Use pg_config --pkglibdir to find out the name of this directory.) For example:

dynamic_library_path = '/usr/local/lib/postgresql:/home/my_project/lib:$libdir'

or, in a Windows environment:

dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'

The default value for this parameter is '$libdir'. If the value is set to an empty string, the automatic path search is turned off.

This parameter can be changed at run time by superusers, but a setting done that way will only persist until the end of the client connection, so this method should be reserved for development purposes. The recommended way to set this parameter is in the postgresql.conf configuration file.

Soft upper limit of the size of the set returned by GIN index. For more information see Section 52.4.

This variable specifies one or more shared libraries that are to be preloaded at connection start. If more than one library is to be loaded, separate their names with commas. This parameter cannot be changed after the start of a particular session.

Because this is not a superuser-only option, the libraries that can be loaded are restricted to those appearing in the plugins subdirectory of the installation's standard library directory. (It is the database administrator's responsibility to ensure that only "safe" libraries are installed there.) Entries in local_preload_libraries can specify this directory explicitly, for example $libdir/plugins/mylib, or just specify the library name — mylib would have the same effect as $libdir/plugins/mylib.

There is no performance advantage to loading a library at session start rather than when it is first used. Rather, the intent of this feature is to allow debugging or performance-measurement libraries to be loaded into specific sessions without an explicit LOAD command being given. For example, debugging could be enabled for all sessions under a given user name by setting this parameter with ALTER USER SET.

If a specified library is not found, the connection attempt will fail.

Every PostgreSQL-supported library has a "magic block" that is checked to guarantee compatibility. For this reason, non-PostgreSQL libraries cannot be loaded in this way.