There are a lot of configuration parameters that affect the behavior
of the database system. Here we describe how to set them and the
following subsections will discuss each in detail.
All parameter names are case-insensitive. Every parameter takes a
value of one of the four types: Boolean, integer, floating point,
and string. Boolean values are ON,
OFF, TRUE,
FALSE, YES,
NO, 1, 0
(case-insensitive) or any non-ambiguous prefix of these.
One way to set these options is to edit the file
postgresql.conf in the data directory. (A
default file is installed there.) An example of what this file might
look like is:
# This is a comment
log_connections = yes
syslog = 2
search_path = '$user, public'
As you see, options are one per line. The equal sign between name
and value is optional. Whitespace is insignificant and blank lines
are ignored. Hash marks ("#") introduce comments
anywhere. Parameter values that are not simple identifiers or
numbers should be single-quoted.
The configuration file is reread whenever the postmaster receives a
SIGHUP signal (which is most easily sent by means of
pg_ctl reload). The postmaster also propagates this
signal to all currently running backend processes so that existing
sessions also get the new value. Alternatively, you can send the
signal to a single backend process directly.
A second way to set these configuration parameters is to give them
as a command line option to the postmaster, such as:
postmaster -c log_connections=yes -c syslog=2
which would have the same effect as the previous example.
Command-line options override any conflicting settings in
postgresql.conf.
Occasionally it is also useful to give a command line option to
one particular backend session only. The environment variable
PGOPTIONS can be used for this purpose on the
client side:
env PGOPTIONS='-c geqo=off' psql
(This works for any libpq-based client application, not just
psql.) Note that this won't work for
options that are fixed when the server is started, such as the port
number.
Some options can be changed in individual SQL sessions with the
SET command, for example:
=> SET ENABLE_SEQSCAN TO OFF;
See the SQL command language reference for details on the syntax.
Furthermore, it is possible to assign a set of option settings to
a user or a database. Whenever a session is started, the default
settings for the user and database involved are loaded. The
commands ALTER DATABASE and ALTER
USER, respectively, are used to configure these settings.
Such per-database settings override anything received from the postmaster
or the configuration file, and in turn are overridden by per-user
settings.
The pg_settings virtual table allows display and update
of current session run-time parameters. There is one entry for each of the
available parameters provided by SHOW ALL. But it is
in a form that allows it to be joined with other relations and have a
selection criteria applied.
An UPDATE performed on 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.
Sets the query optimizer's estimate of the cost of processing
each index tuple during an index scan. This is measured as a
fraction of the cost of a sequential page fetch.
CPU_OPERATOR_COST (floating point)
Sets the optimizer's estimate of the cost of processing each
operator in a WHERE clause. This is measured as a fraction of
the cost of a sequential page fetch.
CPU_TUPLE_COST (floating point)
Sets the query optimizer's estimate of the cost of processing
each tuple during a query. This is measured as a fraction of
the cost of a sequential page fetch.
DEFAULT_STATISTICS_TARGET (integer)
Sets the default statistics target for table columns that have not
had a column-specific target set via ALTER TABLE SET
STATISTICS. Larger values increase the time needed to do
ANALYZE, but may improve the quality of the planner's
estimates.
EFFECTIVE_CACHE_SIZE (floating point)
Sets the optimizer's assumption about the effective size of the
disk cache (that is, the portion of the kernel's disk cache that
will be used for PostgreSQL data
files). This is measured in disk pages, which are normally 8 kB
each.
ENABLE_HASHJOIN (boolean)
Enables or disables the query planner's use of hash-join plan
types. The default is on. This is used for debugging the
query planner.
ENABLE_INDEXSCAN (boolean)
Enables or disables the query planner's use of index-scan plan
types. The default is on. This is used to debugging the
query planner.
ENABLE_MERGEJOIN (boolean)
Enables or disables the query planner's use of merge-join plan
types. The default is on. This is used for debugging the
query planner.
ENABLE_NESTLOOP (boolean)
Enables or disables the query planner's use of nested-loop join
plans. It's not possible to suppress nested-loop joins entirely,
but turning this variable off discourages the planner from using
one if there are other methods available. The default is
on. This is used for debugging the query planner.
ENABLE_SEQSCAN (boolean)
Enables or disables the query planner's use of sequential scan
plan types. It's not possible to suppress sequential scans
entirely, but turning this variable off discourages the planner
from using one if there are other methods available. The
default is on. This is used for debugging the query planner.
ENABLE_SORT (boolean)
Enables or disables the query planner's use of explicit sort
steps. It's not possible to suppress explicit sorts entirely,
but turning this variable off discourages the planner from
using one if there are other methods available. The default
is on. This is used for debugging the query planner.
ENABLE_TIDSCAN (boolean)
Enables or disables the query planner's use of TID scan plan
types. The default is on. This is used for debugging the
query planner.
GEQO (boolean)
Enables or disables genetic query optimization, which is an
algorithm that attempts to do query planning without exhaustive
searching. This is on by default. See also the various other
GEQO_ settings.
Various tuning parameters for the genetic query optimization
algorithm: The pool size is the number of individuals in one
population. Valid values are between 128 and 1024. If it is set
to 0 (the default) a pool size of 2^(QS+1), where QS is the
number of FROM items in the query, is taken. The effort is used
to calculate a default for generations. Valid values are between
1 and 80, 40 being the default. Generations specifies the number
of iterations in the algorithm. The number must be a positive
integer. If 0 is specified then Effort *
Log2(PoolSize) is used. The run time of the algorithm
is roughly proportional to the sum of pool size and generations.
The selection bias is the selective pressure within the
population. Values can be from 1.50 to 2.00; the latter is the
default. The random seed can be set to get reproducible results
from the algorithm. If it is set to -1 then the algorithm
behaves non-deterministically.
GEQO_THRESHOLD (integer)
Use genetic query optimization to plan queries with at least
this many FROM items involved. (Note that a
JOIN construct counts as only one FROM
item.) The default is 11. For simpler queries it is usually best
to use the deterministic, exhaustive planner. This parameter
also controls how hard the optimizer will try to merge subquery
FROM clauses into the upper query.
RANDOM_PAGE_COST (floating point)
Sets the query optimizer's estimate of the cost of a
nonsequentially fetched disk page. This is measured as a
multiple of the cost of a sequential page fetch.
Note: Unfortunately, there is no well-defined method for determining
ideal values for the family of "COST" variables that
were just described. You are encouraged to experiment and share
your findings.
This controls how much message detail is written to the server
logs. Valid values are DEBUG5,
DEBUG4, DEBUG3, DEBUG2,
DEBUG1, INFO, NOTICE,
WARNING, ERROR, LOG,
FATAL, and PANIC. Later values send
less detail to the logs. The default is NOTICE.
Note that LOG has a different precedence here than
in CLIENT_MIN_MESSAGES.
Here is a summary of the various message types:
DEBUG[1-5]
Provides information for use by developers.
INFO
Provides information implicitly requested by the user,
e.g., during VACUUM VERBOSE.
NOTICE
Provides information that may be helpful to users, e.g.,
truncation of long identifiers and index creation as part
of primary keys.
WARNING
Provides warnings to the user, e.g., COMMIT
outside a transaction.
ERROR
Reports the error that caused a transaction to abort.
LOG
Reports information of interest to administrators, e.g.,
checkpoint activity.
FATAL
Reports why a backend session terminated.
PANIC
Reports why all backend sessions restarted.
CLIENT_MIN_MESSAGES (string)
This controls how much message detail is written to the
client. Valid values are DEBUG5,
DEBUG4, DEBUG3, DEBUG2,
DEBUG1, LOG, NOTICE,
WARNING, and ERROR. Later values send
less information to the client. The default is
NOTICE. Note that LOG has a different
precedence here than in SERVER_MIN_MESSAGES. Also
see that section for an explanation of the various values.
DEBUG_ASSERTIONS (boolean)
Turns on various assertion checks. This is a debugging aid. If
you are experiencing strange problems or crashes you might want
to turn this on, as it might expose programming mistakes. To use
this option, the macro USE_ASSERT_CHECKING
must be defined when PostgreSQL is
built (accomplished by the configure option
--enable-cassert). Note that
DEBUG_ASSERTIONS defaults to on if
PostgreSQL has been built with
assertions enabled.
These flags enable various debugging output to be sent to the
server log. For each executed query, print either the query text,
the resulting parse tree, the query rewriter output, or the execution
plan. DEBUG_PRETTY_PRINT indents these displays
to produce a more readable but much longer output format.
EXPLAIN_PRETTY_PRINT (boolean)
Determines whether EXPLAIN VERBOSE uses the indented
or non-indented format for displaying detailed query-tree dumps.
HOSTNAME_LOOKUP (boolean)
By default, connection logs only show the IP address of the
connecting host. If you want it to show the host name you can
turn this on, but depending on your host name resolution setup
it might impose a non-negligible performance penalty. This
option can only be set at server start.
LOG_CONNECTIONS (boolean)
This outputs a line to the server logs detailing each successful
connection. This is off by default, although it is probably very
useful. This option can only be set at server start or in the
postgresql.conf configuration file.
LOG_DURATION (boolean)
Causes the duration of every completed statement to be logged.
To use this option, enable LOG_STATEMENT and
LOG_PID so you can link the statement to the
duration using the process ID.
LOG_MIN_ERROR_STATEMENT (string)
This controls for which message levels the SQL statement
causing that message is to be recorded in the server log. All
statements causing a message of the level of the setting or
higher are logged. The default is PANIC
(effectively turning this feature off). Valid values are
DEBUG5, DEBUG4,
DEBUG3, DEBUG2,
DEBUG1, INFO,
NOTICE, WARNING,
ERROR, FATAL, and
PANIC. For example, if you set this to
ERROR then all SQL statements causing
errors, fatal errors, or panics will be logged.
It is recommended you enable LOG_PID as well
so you can more easily match the error statement with the error
message.
LOG_PID (boolean)
Prefixes each server message in the log file with the process ID of
the backend process. This is useful to sort out which messages
pertain to which connection. The default is off. This parameter
does not affect messages logged via syslog, which always contain
the process ID.
LOG_STATEMENT (boolean)
Causes each SQL statement to be logged.
LOG_TIMESTAMP (boolean)
Prefixes each server log message with a time stamp. The default
is off.
For each query, write performance statistics of the respective
module to the server log. This is a crude profiling
instrument.
SHOW_SOURCE_PORT (boolean)
Shows the outgoing port number of the connecting host in the
connection log messages. You could trace back the port number
to find out what user initiated the connection. Other than
that, it's pretty useless and therefore off by default. This
option can only be set at server start.
These flags determine what information backends send to the statistics
collector process: current commands, block-level activity statistics,
or row-level activity statistics. All default to off. Enabling
statistics collection costs a small amount of time per query, but
is invaluable for debugging and performance tuning.
STATS_RESET_ON_SERVER_START (boolean)
If on, collected statistics are zeroed out whenever the server
is restarted. If off, statistics are accumulated across server
restarts. The default is on. This option can only be set at
server start.
STATS_START_COLLECTOR (boolean)
Controls whether the server should start the statistics-collection
subprocess. This is on by default, but may be turned off if you
know you have no interest in collecting statistics. This option
can only be set at server start.
SYSLOG (integer)
PostgreSQL allows the use of
syslog for logging. If this option is
set to 1, messages go both to syslog and the
standard output. A setting of 2 sends output only to
syslog. (Some messages will still go to the
standard output/error.) The default is 0, which means
syslog is off. This option must be set at server
start.
SYSLOG_FACILITY (string)
This option determines the syslog"facility" to be used when
syslog is enabled. You may choose
from LOCAL0, LOCAL1,
LOCAL2, LOCAL3, LOCAL4,
LOCAL5, LOCAL6, LOCAL7;
the default is LOCAL0. See also the
documentation of your system's
syslog.
SYSLOG_IDENT (string)
If logging to syslog is enabled, this option
determines the program name used to identify
PostgreSQL messages in
syslog log messages. The default is
postgres.
TRACE_NOTIFY (boolean)
Generates a great amount of debugging output for the
LISTEN and NOTIFY
commands.
If set to true, PostgreSQL will
automatically do a COMMIT after each successful command
that is not inside an explicit transaction block (that is, unless a
BEGIN with no matching COMMIT has been
given).
If set to false, PostgreSQL will
commit only upon receiving an explicit
COMMIT command. This mode can also be thought of as
implicitly issuing BEGIN whenever a command is
received that is not already inside a transaction block. The
default is true, for compatibility with historical
PostgreSQL behavior. However, for
maximum compatibility with the SQL specification, set it to
false.
Note: Even with autocommit set to false, SET,
SHOW, and RESET do not start new
transaction blocks. They are run in their own transactions.
Once another command is issued, a transaction block
begins and any SET, SHOW, or
RESET commands are considered to be part of the
transaction, i.e., they are committed or rolled back depending
on the completion status of the transaction. To execute a
SET, SHOW, or RESET
command at the start of a transaction block, use BEGIN
first.
Note: As of PostgreSQL 7.3, setting
autocommit to false is not well-supported.
This is a new feature and is not yet handled by all client
libraries and applications. Before making it the default
setting in your installation, test carefully.
AUSTRALIAN_TIMEZONES (boolean)
If set to true, CST, EST,
and SAT are interpreted as Australian
time zones rather than as North American Central/Eastern
time zones and Saturday. The default is false.
AUTHENTICATION_TIMEOUT (integer)
Maximum time to complete client authentication, in seconds. If a
would-be client has not completed the authentication protocol in
this much time, the server breaks the connection. This prevents
hung clients from occupying a connection indefinitely. This
option can only be set at server start or in the
postgresql.conf file.
CLIENT_ENCODING (string)
Sets the client-side encoding for multibyte character sets.
The default is to use the database encoding.
DATESTYLE (string)
Sets the display format for dates, as well as the rules for
interpreting ambiguous input dates.
The default is ISO, US.
DB_USER_NAMESPACE (boolean)
This allows per-database user names. It is off by default.
If this is on, create users as username@dbname.
When username is passed by a connecting client,
@ and the database name is appended to the user
name and that database-specific user name is looked up by the
server. Note that when you create users with names containing
@ within the SQL environment, you will need to
quote the user name.
With this option enabled, you can still create ordinary global
users. Simply append @ when specifying the user
name in the client. The @ will be stripped off
before the user name is looked up by the server.
Note: This feature is intended as a temporary measure until a
complete solution is found. At that time, this option will
be removed.
DEADLOCK_TIMEOUT (integer)
This is the amount of time, in milliseconds, to wait on a lock
before checking to see if there is a deadlock condition. The
check for deadlock is relatively slow, so the server doesn't run
it every time it waits for a lock. We (optimistically?) assume
that deadlocks are not common in production applications and
just wait on the lock for a while before starting check for a
deadlock. Increasing this value reduces the amount of time
wasted in needless deadlock checks, but slows down reporting of
real deadlock errors. The default is 1000 (i.e., one second),
which is probably about the smallest value you would want in
practice. On a heavily loaded server you might want to raise it.
Ideally the setting should exceed your typical transaction time,
so as to improve the odds that the lock will be released before
the waiter decides to check for deadlock. This option can only
be set at server start.
DEFAULT_TRANSACTION_ISOLATION (string)
Each SQL transaction has an isolation level, which can be either
"read committed" or "serializable".
This parameter controls the default isolation level of each new
transaction. The default is "read committed".
If a dynamically loadable module needs to be opened and the
specified name does not have a directory component (i.e. the
name does not contain a slash), the system will search this
path for the specified file. (The name that is used is the
name specified in the CREATE FUNCTION or
LOAD command.)
The value for dynamic_library_path has to be a colon-separated
list of absolute directory names. If a directory name starts
with the special value $libdir, the
compiled-in PostgreSQL package
library directory is substituted. This where the modules
provided by the PostgreSQL
distribution are installed. (Use pg_config
--pkglibdir to print the name of this directory.) For
example:
The default value for this parameter is
'$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.
KRB_SERVER_KEYFILE (string)
Sets the location of the Kerberos server key file. See
Section 6.2.3 for details.
FSYNC (boolean)
If this option is on, the PostgreSQL backend
will use the fsync() system call in several places
to make sure that updates are physically written to disk. This
insures that a database installation will recover to a
consistent state after an operating system or hardware crash.
(Crashes of the database server itself are not
related to this.)
However, this operation does slow down
PostgreSQL because at transaction commit it has
wait for the operating system to flush the write-ahead log.
Without fsync, the operating system is allowed to
do its best in buffering, sorting, and delaying writes, which
can considerably increase performance. However, if the system
crashes, the results of the last few committed transactions may
be lost in part or whole. In the worst case, unrecoverable data
corruption may occur.
For the above reasons, some administrators always leave it off,
some turn it off only for bulk loads, where there is a clear
restart point if something goes wrong, and some leave it on just
to be on the safe side. Because it is always safe, the default
is on. If you trust your operating system, your hardware, and
your utility company (or better your UPS), you might want to
disable fsync.
It should be noted that the performance penalty of doing
fsyncs is considerably less in
PostgreSQL version 7.1 and later. If you
previously suppressed fsyncs for performance
reasons, you may wish to reconsider your choice.
This option can only be set at server start or in the
postgresql.conf file.
LC_MESSAGES (string)
Sets the language in which messages are displayed. Acceptable
values are system-dependent; see Section 7.1 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.
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 7.1 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 7.1 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 date and time values.
(Currently, this setting does nothing, but it may in the
future.) Acceptable values are system-dependent; see Section 7.1 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.
MAX_CONNECTIONS (integer)
Determines the maximum number of concurrent connections to the
database server. The default is 32 (unless altered while
building the server). This parameter can only be set at server
start.
MAX_EXPR_DEPTH (integer)
Sets the maximum expression nesting depth of the parser. The
default value is high enough for any normal query, but you can
raise it if needed. (But if you raise it too high, you run
the risk of backend crashes due to stack overflow.)
MAX_FILES_PER_PROCESS (integer)
Sets the maximum number of simultaneously open files in each
server subprocess. The default is 1000. The limit actually used
by the code is the smaller of this setting and the result of
sysconf(_SC_OPEN_MAX). Therefore, on systems
where sysconf returns a reasonable limit, you don't
need to worry about this setting. But on some platforms
(notably, most BSD systems), sysconf returns a
value that is much larger than the system can really support
when a large number of processes all try to open that many
files. If you find yourself seeing "Too many open files"
failures, try reducing this setting. This option can only be set
at server start or in the postgresql.conf
configuration file; if changed in the configuration file, it
only affects subsequently-started server subprocesses.
MAX_FSM_RELATIONS (integer)
Sets the maximum number of relations (tables) for which free
space will be tracked in the shared free-space map. The default
is 100. This option can only be set at server start.
MAX_FSM_PAGES (integer)
Sets the maximum number of disk pages for which free space will
be tracked in the shared free-space map. The default is 10000.
This option can only be set at server start.
MAX_LOCKS_PER_TRANSACTION (integer)
The shared lock table is sized on the assumption that at most
max_locks_per_transaction *
max_connections distinct objects will need to
be locked at any one time. The default, 64, which has historically
proven sufficient, but you might need to raise this value if you
have clients that touch many different tables in a single
transaction. This option can only be set at server start.
PASSWORD_ENCRYPTION (boolean)
When a password is specified in CREATE USER or
ALTER USER without writing either ENCRYPTED or
UNENCRYPTED, this flag determines whether the password is to be
encrypted. The default is on (encrypt the password).
PORT (integer)
The TCP port the server listens on; 5432 by default. This
option can only be set at server start.
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 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 same name as the SESSION_USER is substituted, if there
is such a schema. (If not, $user is ignored.)
The system catalog schema, pg_catalog, is always
searched, whether it is mentioned in the path or not. If it is
mentioned in the path then it will be searched in the specified
order. If pg_catalog is not in the path then it will
be searched before searching any of the path items.
It should also be noted that the temporary-table schema,
pg_temp_nnn, is implicitly searched before any of
these.
When objects are created without specifying a particular target
schema, they will be placed in the first schema listed
in the search path. An error is reported if the search path is
empty.
The default value for this parameter is
'$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.
Aborts any statement that takes over the specified number of
milliseconds. A value of zero turns off the timer.
SHARED_BUFFERS (integer)
Sets the number of shared memory buffers used by the database
server. The default is 64. Each buffer is typically 8192 bytes.
This option can only be set at server start.
SILENT_MODE (bool)
Runs the server silently. If this option is set, the server
will automatically run in background and any controlling ttys
are disassociated, thus no messages are written to standard
output or standard error (same effect as postmaster's -S
option). Unless some logging system such as
syslog is enabled, using this option is
discouraged since it makes it impossible to see error messages.
SORT_MEM (integer)
Specifies the amount of memory to be used by internal sorts and
hashes before switching to temporary disk files. The value is
specified in kilobytes, and defaults to 1024 kilobytes (1 MB).
Note that for a complex query, several sorts might be running in
parallel, and each one will be allowed to use as much memory as
this value specifies before it starts to put data into temporary
files. Also, each running backend could be doing one or more
sorts simultaneously, so the total memory used could be many
times the value of SORT_MEM. Sorts are used
by ORDER BY, merge joins, and CREATE INDEX.
SQL_INHERITANCE (bool)
This controls the inheritance semantics, in particular whether
subtables are included by various commands by default. They were
not included in versions prior to 7.1. If you need the old
behavior you can set this variable to off, but in the long run
you are encouraged to change your applications to use the
ONLY keyword to exclude subtables. See the
SQL language reference and the PostgreSQL 7.3 User's Guide for more information about inheritance.
SSL (boolean)
Enables SSL connections. Please read
Section 3.7 before using this. The default
is off.
SUPERUSER_RESERVED_CONNECTIONS
(integer)
Determines the number of "connection slots" that
are reserved for connections by PostgreSQL
superusers. At most max_connections connections can
ever be active simultaneously. Whenever the number of active
concurrent connections is at least max_connections minus
superuser_reserved_connections, new connections
will be accepted only from superuser accounts.
The default value is 2. The value must be less than the value of
max_connections. This parameter can only be
set at server start.
TCPIP_SOCKET (boolean)
If this is true, then the server will accept TCP/IP connections.
Otherwise only local Unix domain socket connections are
accepted. It is off by default. This option can only be set at
server start.
TIMEZONE (string)
Sets the time zone for displaying and interpreting timestamps.
The default is to use whatever the system environment
specifies as the time zone.
TRANSFORM_NULL_EQUALS (boolean)
When turned on, expressions of the form
expr = NULL (or NULL
= expr) are treated as
expr IS NULL, that is, they
return true if expr evaluates to the null value,
and false otherwise. The correct behavior of
expr = NULL is to always
return null (unknown). Therefore this option defaults to off.
However, filtered forms in Microsoft
Access generate queries that appear to use
expr = NULL to test for
null values, so if you use that interface to access the database you
might want to turn this option on. Since expressions of the
form expr = NULL always
return the null value (using the correct interpretation) they are not
very useful and do not appear often in normal applications, so
this option does little harm in practice. But new users are
frequently confused about the semantics of expressions
involving null values, so this option is not on by default.
Note that this option only affects the literal =
operator, not other comparison operators or other expressions
that are computationally equivalent to some expression
involving the equals operator (such as IN).
Thus, this option is not a general fix for bad programming.
Specifies the directory of the Unix-domain socket on which the
server is to listen for
connections from client applications. The default is normally
/tmp, but can be changed at build time.
UNIX_SOCKET_GROUP (string)
Sets the group owner of the Unix domain socket. (The owning
user of the socket is always the user that starts the
server.) In combination with the option
UNIX_SOCKET_PERMISSIONS this can be used as
an additional access control mechanism for this socket type.
By default this is the empty string, which uses the default
group for the current user. This option can only be set at
server start.
UNIX_SOCKET_PERMISSIONS (integer)
Sets the access permissions of the Unix domain socket. Unix
domain sockets use the usual Unix file system permission set.
The option value is expected to be an numeric mode
specification in the form accepted by the
chmod and umask
system calls. (To use the customary octal format the number
must start with a 0 (zero).)
The default permissions are 0777, meaning
anyone can connect. Reasonable alternatives are
0770 (only user and group, see also under
UNIX_SOCKET_GROUP) and 0700
(only user). (Note that actually for a Unix domain socket, only write
permission matters and there is no point in setting or revoking
read or execute permissions.)
This access control mechanism is independent of the one
described in Chapter 6.
This option can only be set at server start.
VACUUM_MEM (integer)
Specifies the maximum amount of memory to be used by
VACUUM to keep track of to-be-reclaimed
tuples. The value is specified in kilobytes, and defaults to
8192 kilobytes. Larger settings may improve the speed of
vacuuming large tables that have many deleted tuples.
VIRTUAL_HOST (string)
Specifies the TCP/IP host name or address on which the
postmaster is to listen for
connections from client applications. Defaults to listening on
all configured addresses (including localhost).
Maximum distance between automatic WAL checkpoints, in log file
segments (each segment is normally 16 megabytes).
This option can only be set at server start or in the
postgresql.conf file.
CHECKPOINT_TIMEOUT (integer)
Maximum time between automatic WAL checkpoints, in seconds.
This option can only be set at server start or in the
postgresql.conf file.
COMMIT_DELAY (integer)
Time delay between writing a commit record to the WAL buffer and
flushing the buffer out to disk, in microseconds. A nonzero
delay allows multiple transactions to be committed with only one
fsync system call, if system load is high
enough additional transactions may become ready to commit within
the given interval. But the delay is just wasted if no other
transactions become ready to commit. Therefore, the delay is
only performed if at least COMMIT_SIBLINGS other transactions
are active at the instant that a backend process has written its commit
record.
COMMIT_SIBLINGS (integer)
Minimum number of concurrent open transactions to require before
performing the COMMIT_DELAY delay. A larger value
makes it more probable that at least one other transaction will
become ready to commit during the delay interval.
WAL_BUFFERS (integer)
Number of disk-page buffers in shared memory for WAL logging.
This option can only be set at server start.
WAL_DEBUG (integer)
If nonzero, turn on WAL-related debugging output on standard
error.
WAL_SYNC_METHOD (string)
Method used for forcing WAL updates out to disk. Possible
values are
FSYNC (call fsync() at each commit),
FDATASYNC (call fdatasync() at each commit),
OPEN_SYNC (write WAL files with open() option O_SYNC), or
OPEN_DATASYNC (write WAL files with open() option O_DSYNC).
Not all of these choices are available on all platforms.
This option can only be set at server start or in the
postgresql.conf file.
