19.11. Client Connection Defaults
19.11.2. Locale and Formatting
19.11.3. Shared Library Preloading
19.11.1. Statement Behavior
client_min_messages (enum) : Controls which message levels are sent to the client. Valid values are DEBUG5, DEBUG4, DEBUG3, DEBUG2, DEBUG1, LOG, NOTICE, WARNING, and ERROR. Each level includes all the levels that follow it. The later the level, the fewer messages are sent. The default is NOTICE. Note that LOG has a different rank here than in log_min_messages.
`INFO` level messages are always sent to the client.
search_path (string) : 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 specified. 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` must be a comma-separated
list of schema names. Any name that is not an existing schema, or is
a schema for which the user does not have `USAGE`
permission, is silently ignored.
If one of the list items is the special name
`$user`, then the schema having the name returned by
`CURRENT_USER` is substituted, if there is such a schema
and the user has `USAGE` permission for it.
(If not, `$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 (even before `pg_catalog`). However,
the temporary schema is only searched for relation (table, view,
sequence, etc) and data type names. It is never searched for
function or operator names.
When objects are created without specifying a particular target
schema, they will be placed in the first valid schema named in
`search_path`. An error is reported if the search
path is empty.
The default value for this parameter is
`"$user", public`.
This setting 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.
For more information on schema handling, see
[Section 5.8](ddl-schemas.md "5.8. Schemas"). In particular, the default
configuration is suitable only when the database has a single user or
a few mutually-trusting users.
The current effective value of the search path can be examined
via the SQL function
`current_schemas`
(see [Section 9.25](functions-info.md "9.25. System Information Functions")).
This is not quite the same as
examining the value of `search_path`, since
`current_schemas` shows how the items
appearing in `search_path` were resolved.
row_security (boolean) : This variable controls whether to raise an error in lieu of applying a row security policy. When set to on, policies apply normally. When set to off, queries fail which would otherwise apply at least one policy. The default is on. Change to off where limited row visibility could cause incorrect results; for example, pg_dump makes that change by default. This variable has no effect on roles which bypass every row security policy, to wit, superusers and roles with the BYPASSRLS attribute.
For more information on row security policies,
see [CREATE POLICY](sql-createpolicy.md "CREATE POLICY").
default_tablespace (string) : 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](runtime-config-client.md#GUC-TEMP-TABLESPACES) is consulted instead.
This variable is also not used when creating databases.
By default, a new database inherits its tablespace setting from
the template database it is copied from.
For more information on tablespaces,
see [Section 22.6](manage-ag-tablespaces.md "22.6. Tablespaces").
temp_tablespaces (string) : This variable specifies tablespaces 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 tablespaces.
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](runtime-config-client.md#GUC-DEFAULT-TABLESPACE).
check_function_bodies (boolean) : This parameter is normally on. When set to off, it disables validation of the function body string during CREATE FUNCTION. Disabling validation avoids side effects of the validation process and avoids false positives due to problems such as forward references. Set this parameter to off before loading functions on behalf of other users; pg_dump does so automatically.
default_transaction_isolation (enum) : 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](mvcc.md "Chapter 13. Concurrency Control") and [SET TRANSACTION](sql-set-transaction.md "SET TRANSACTION") for more information.
default_transaction_read_only (boolean) : 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](sql-set-transaction.md "SET TRANSACTION") for more information.
default_transaction_deferrable (boolean) : When running at the serializable isolation level, a deferrable read-only SQL transaction may be delayed before it is allowed to proceed. However, once it begins executing it does not incur any of the overhead required to ensure serializability; so serialization code will have no reason to force it to abort because of concurrent updates, making this option suitable for long-running read-only transactions.
This parameter controls the default deferrable status of each
new transaction. It currently has no effect on read-write
transactions or those operating at isolation levels lower
than `serializable`. The default is `off`.
Consult [SET TRANSACTION](sql-set-transaction.md "SET TRANSACTION") for more information.
session_replication_role (enum) : 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.
The intended use of this setting is that logical replication systems
set it to `replica` when they are applying replicated
changes. The effect of that will be that triggers and rules (that
have not been altered from their default configuration) will not fire
on the replica. See the [ALTER TABLE](sql-altertable.md "ALTER TABLE") clauses
`ENABLE TRIGGER` and `ENABLE RULE`
for more information.
PostgreSQL treats the settings `origin` and
`local` the same internally. Third-party replication
systems may use these two values for their internal purposes, for
example using `local` to designate a session whose
changes should not be replicated.
Since foreign keys are implemented as triggers, setting this parameter
to `replica` also disables all foreign key checks,
which can leave data in an inconsistent state if improperly used.
statement_timeout (integer) : Abort any statement that takes more than 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 this off.
Setting `statement_timeout` in
`postgresql.conf` is not recommended because it would
affect all sessions.
lock_timeout (integer) : Abort any statement that waits longer than the specified number of milliseconds while attempting to acquire a lock on a table, index, row, or other database object. The time limit applies separately to each lock acquisition attempt. The limit applies both to explicit locking requests (such as LOCK TABLE, or SELECT FOR UPDATE without NOWAIT) and to implicitly-acquired locks. If log_min_error_statement is set to ERROR or lower, the statement that timed out will be logged. A value of zero (the default) turns this off.
Unlike `statement_timeout`, this timeout can only occur
while waiting for locks. Note that if `statement_timeout`
is nonzero, it is rather pointless to set `lock_timeout` to
the same or larger value, since the statement timeout would always
trigger first.
Setting `lock_timeout` in
`postgresql.conf` is not recommended because it would
affect all sessions.
idle_in_transaction_session_timeout (integer) : Terminate any session with an open transaction that has been idle for longer than the specified duration in milliseconds. This allows any locks held by that session to be released and the connection slot to be reused; it also allows tuples visible only to this transaction to be vacuumed. See Section 24.1 for more details about this.
The default value of 0 disables this feature.
vacuum_freeze_table_age (integer) : VACUUM performs an aggressive scan if the table's pg_class.relfrozenxid field has reached the age specified by this setting. An aggressive scan differs from a regular VACUUM in that it visits every page that might contain unfrozen XIDs or MXIDs, not just those that might contain dead tuples. The default is 150 million transactions. Although users can set this value anywhere from zero to two billions, 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 24.1.5.
vacuum_freeze_min_age (integer) : Specifies the cutoff age (in transactions) that VACUUM should use to decide whether to freeze row versions 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 24.1.5.
vacuum_multixact_freeze_table_age (integer) : VACUUM performs an aggressive scan if the table's pg_class.relminmxid field has reached the age specified by this setting. An aggressive scan differs from a regular VACUUM in that it visits every page that might contain unfrozen XIDs or MXIDs, not just those that might contain dead tuples. The default is 150 million multixacts. Although users can set this value anywhere from zero to two billions, VACUUM will silently limit the effective value to 95% of autovacuum_multixact_freeze_max_age, so that a periodical manual VACUUM has a chance to run before an anti-wraparound is launched for the table. For more information see Section 24.1.5.1.
vacuum_multixact_freeze_min_age (integer) : Specifies the cutoff age (in multixacts) that VACUUM should use to decide whether to replace multixact IDs with a newer transaction ID or multixact ID while scanning a table. The default is 5 million multixacts. 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_multixact_freeze_max_age, so that there is not an unreasonably short time between forced autovacuums. For more information see Section 24.1.5.1.
vacuum_cleanup_index_scale_factor (floating point) : Specifies the fraction of the total number of heap tuples counted in the previous statistics collection that can be inserted without incurring an index scan at the VACUUM cleanup stage. This setting currently applies to B-tree indexes only.
If no tuples were deleted from the heap, B-tree indexes are still
scanned at the `VACUUM` cleanup stage when at least one
of the following conditions is met: the index statistics are stale, or
the index contains deleted pages that can be recycled during cleanup.
Index statistics are considered to be stale if the number of newly
inserted tuples exceeds the `vacuum_cleanup_index_scale_factor`
fraction of the total number of heap tuples detected by the previous
statistics collection. The total number of heap tuples is stored in
the index meta-page. Note that the meta-page does not include this data
until `VACUUM` finds no dead tuples, so B-tree index
scan at the cleanup stage can only be skipped if the second and
subsequent `VACUUM` cycles detect no dead tuples.
The value can range from `0` to
`10000000000`.
When `vacuum_cleanup_index_scale_factor` is set to
`0`, index scans are never skipped during
`VACUUM` cleanup. The default value is `0.1`.
bytea_output (enum) : Sets the output format for values of type bytea. Valid values are hex (the default) and escape (the traditional PostgreSQL format). See Section 8.4 for more information. The bytea type always accepts both formats on input, regardless of this setting.
xmlbinary (enum) : 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.
xmloption (enum) : 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
```synopsis
SET XML OPTION { DOCUMENT | CONTENT };
```
This syntax is also available in PostgreSQL.
gin_pending_list_limit (integer) : Sets the maximum size of the GIN pending list which is used when fastupdate is enabled. If the list grows larger than this maximum size, it is cleaned up by moving the entries in it to the main GIN data structure in bulk. The default is four megabytes (4MB). This setting can be overridden for individual GIN indexes by changing index storage parameters. See Section 66.4.1 and Section 66.5 for more information.
19.11.2. Locale and Formatting
DateStyle (string) : 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.
IntervalStyle (enum) : 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](datatype-datetime.md#DATATYPE-INTERVAL-INPUT "8.5.4. Interval Input") for more information.
TimeZone (string) : Sets the time zone for displaying and interpreting time stamps. The built-in default is GMT, but that is typically overridden in postgresql.conf; initdb will install a setting there corresponding to its system environment. See Section 8.5.3 for more information.
timezone_abbreviations (string) : 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 Section B.4 for more information.
extra_float_digits (integer) : 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 3, 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. See also Section 8.1.3.
client_encoding (string) : Sets the client-side encoding (character set). The default is to use the database encoding. The character sets supported by the PostgreSQL server are described in Section 23.3.1.
lc_messages (string) : Sets the language in which messages are displayed. Acceptable values are system-dependent; see Section 23.1 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, and
an improper value might obscure the readability of the server
logs.
lc_monetary (string) : 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 23.1 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.
lc_numeric (string) : Sets the locale to use for formatting numbers, for example with the to_char family of functions. Acceptable values are system-dependent; see Section 23.1 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.
lc_time (string) : 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 23.1 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.
default_text_search_config (string) : 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.
19.11.3. Shared Library Preloading
Several settings are available for preloading shared libraries into the server, in order to load additional functionality or achieve performance benefits. For example, a setting of '$libdir/mylib' would cause mylib.so (or on some platforms, mylib.sl) to be preloaded from the installation's standard library directory. The differences between the settings are when they take effect and what privileges are required to change them.
PostgreSQL procedural language libraries can be preloaded in this way, typically by using the syntax '$libdir/plXXX' where XXX is pgsql, perl, tcl, or python.
Only shared libraries specifically intended to be used with PostgreSQL can be loaded this way. Every PostgreSQL-supported library has a “magic block” that is checked to guarantee compatibility. For this reason, non-PostgreSQL libraries cannot be loaded in this way. You might be able to use operating-system facilities such as LD_PRELOAD for that.
In general, refer to the documentation of a specific module for the recommended way to load that module.
local_preload_libraries (string) : This variable specifies one or more shared libraries that are to be preloaded at connection start. It contains a comma-separated list of library names, where each name is interpreted as for the LOAD command. Whitespace between entries is ignored; surround a library name with double quotes if you need to include whitespace or commas in the name. The parameter value only takes effect at the start of the connection. Subsequent changes have no effect. If a specified library is not found, the connection attempt will fail.
This option can be set by any user. Because of that, the libraries
that can be loaded are restricted to those appearing in the
`plugins` subdirectory of the installation's
standard library directory. (It is the database administrator's
responsibility to ensure that only “safe” libraries
are installed there.) Entries in `local_preload_libraries`
can specify this directory explicitly, for example
`$libdir/plugins/mylib`, or just specify
the library name — `mylib` would have
the same effect as `$libdir/plugins/mylib`.
The intent of this feature is to allow unprivileged users to load
debugging or performance-measurement libraries into specific sessions
without requiring an explicit `LOAD` command. To that end,
it would be typical to set this parameter using
the `PGOPTIONS` environment variable on the client or by
using
`ALTER ROLE SET`.
However, unless a module is specifically designed to be used in this way by
non-superusers, this is usually not the right setting to use. Look
at [session_preload_libraries](runtime-config-client.md#GUC-SESSION-PRELOAD-LIBRARIES) instead.
session_preload_libraries (string) : This variable specifies one or more shared libraries that are to be preloaded at connection start. It contains a comma-separated list of library names, where each name is interpreted as for the LOAD command. Whitespace between entries is ignored; surround a library name with double quotes if you need to include whitespace or commas in the name. The parameter value only takes effect at the start of the connection. Subsequent changes have no effect. If a specified library is not found, the connection attempt will fail. Only superusers can change this setting.
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, [auto_explain](auto-explain.md "F.4. auto_explain") could be enabled for all
sessions under a given user name by setting this parameter
with `ALTER ROLE SET`. Also, this parameter can be changed
without restarting the server (but changes only take effect when a new
session is started), so it is easier to add new modules this way, even
if they should apply to all sessions.
Unlike [shared_preload_libraries](runtime-config-client.md#GUC-SHARED-PRELOAD-LIBRARIES), there is no large
performance advantage to loading a library at session start rather than
when it is first used. There is some advantage, however, when
connection pooling is used.
shared_preload_libraries (string) : This variable specifies one or more shared libraries to be preloaded at server start. It contains a comma-separated list of library names, where each name is interpreted as for the LOAD command. Whitespace between entries is ignored; surround a library name with double quotes if you need to include whitespace or commas in the name. This parameter can only be set at server start. If a specified library is not found, the server will fail to start.
Some libraries need to perform certain operations that can only take
place at postmaster start, such as allocating shared memory, reserving
light-weight locks, or starting background workers. Those libraries
must be loaded at server start through this parameter. See the
documentation of each library for details.
Other libraries can also be preloaded. By preloading a shared library,
the library startup time is avoided when the library is first used.
However, the time to start each new server process might increase
slightly, even if that process never uses the library. So this
parameter is recommended only for libraries that will be used in most
sessions. Also, changing this parameter requires a server restart, so
this is not the right setting to use for short-term debugging tasks,
say. Use [session_preload_libraries](runtime-config-client.md#GUC-SESSION-PRELOAD-LIBRARIES) for that
instead.
### Note
On Windows hosts, preloading a library at server start will not reduce
the time required to start each new server process; each server process
will re-load all preload libraries. However, `shared_preload_libraries` is still useful on Windows hosts for libraries that need to
perform operations at postmaster start time.
jit_provider (string) : This variable is the name of the JIT provider library to be used (see Section 32.4.2). The default is llvmjit. This parameter can only be set at server start.
If set to a non-existent library, JIT will not be
available, but no error will be raised. This allows JIT support to be
installed separately from the main
PostgreSQL package.
19.11.4. Other Defaults
dynamic_library_path (string) : 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` must 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 `$libdir`; this
is where the modules provided by the standard
PostgreSQL distribution are installed.
(Use `pg_config --pkglibdir` to find out the name of
this directory.) For example:
```programlisting
dynamic_library_path = '/usr/local/lib/postgresql:/home/my_project/lib:$libdir'
```
or, in a Windows environment:
```programlisting
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.
gin_fuzzy_search_limit (integer) : Soft upper limit of the size of the set returned by GIN index scans. For more information see Section 66.5.