Server Runtime Environment
This chapter discusses how to set up and run the database server
and the interactions with the operating system.
The PostgreSQL user accountpostgres user
As with any other server daemon that is connected to outside world,
it is advisable to run PostgreSQL under a
separate user account. This user account should only own the data
that is managed by the server, and should not be shared with other
daemons. (For example, using the user nobody is a bad
idea.) It is not advisable to install executables owned by
this user because compromised systems could then modify their own
binaries.
To add a Unix user account to your system, look for a command
useradd or adduser. The user
name postgres is often used but is by no
means required.
Creating a database clusterdatabase clusterdata areadatabase cluster
Before you can do anything, you must initialize a database storage
area on disk. We call this a database cluster.
(SQL uses the term catalog cluster instead.) A
database cluster is a collection of databases is accessible by a
single instance of a running database server. After initialization, a
database cluster will contain a database named
template1. As the name suggests, this will be used
as a template for subsequently created databases; it should not be
used for actual work.
In file system terms, a database cluster will be a single directory
under which all data will be stored. We call this the data
directory or data area. It is
completely up to you where you choose to store your data. There is no
default, although locations such as
/usr/local/pgsql/data or
/var/lib/pgsql/data are popular. To initialize a
database cluster, use the command initdb, which is
installed with PostgreSQL. The desired
file system location of your database system is indicated by the
option, for example
$> initdb -D /usr/local/pgsql/data
Note that you must execute this command while logged into the
PostgreSQL user account, which is
described in the previous section.
PGDATA
As an alternative to the option, you can set
the environment variable PGDATA.
initdb will attempt to create the directory you
specify if it does not already exist. It is likely that it will not
have the permission to do so (if you followed our advice and created
an unprivileged account). In that case you should create the
directory yourself (as root) and change the owner to be the
PostgreSQL user. Here is how this might
be done:
root# mkdir /usr/local/pgsql/data
root# chown postgres /usr/local/pgsql/data
root# su postgres
postgres$ initdb -D /usr/local/pgsql/datainitdb will refuse to run if the data directory
looks like it it has already been initialized.
Because the data directory contains all the data stored in the
database, it is essential that it be secured from unauthorized
access. initdb therefore revokes access
permissions from everyone but the
PostgreSQL user.
However, while the directory contents are secure, the default
pg_hba.conf authentication method of
trust allows any local user to connect to the
database and even become the database superuser. If you don't trust
other local users, we recommend you use initdb's
or option to assign a
password to the database superuser. After initdb,
modify pg_hba.conf to use md5> or
password> instead of trust> authentication
before> you start the server for the first time. (Other,
approaches include using ident authentication or
file system permissions to restrict connections. See for more information.
LC_COLLATE>>
One surprise you might encounter while running
initdb is a notice similar to this:
WARNING: Initializing database with en_US collation order.
This locale setting will prevent use of index optimization for
LIKE and regexp searches. If you are concerned about speed of
such queries, you may wish to set LC_COLLATE to "C" and
re-initdb. For more information see the Administrator's Guide.
This is intended to warn you that the currently selected locale will
cause indexes to be sorted in an order that prevents them from being
used for LIKE and regular-expression searches. If you need good
performance in such searches, you should set your current locale to
C> and re-run initdb. On most systems,
setting the current locale is done by changing the value of the
environment variable LC_ALL or
LANG. The sort order used within a particular
database cluster is set by initdb and cannot be
changed later, short of dumping all data, rerunning
initdb, and reloading the data. So it's important
to make this choice correctly the first time.
Starting the database serverpostmaster
Before anyone can access the database, you must start the database
server. The database server is called
postmaster. The postmaster must know where to
find the data it is supposed to use. This is done with the
option. Thus, the simplest way to start the
server is:
$ postmaster -D /usr/local/pgsql/data
which will leave the server running in the foreground. This must be
done while logged into the PostgreSQL user
account. Without , the server will try to use
the data directory in the environment variable PGDATA.
If neither of these succeed, it will fail.
To start the postmaster in the
background, use the usual shell syntax:
$ postmaster -D /usr/local/pgsql/data > logfile 2>&1 &
It is an important to store the server's stdout> and
stderr> output somewhere, as shown above. It will help
for auditing purposes and to diagnose problems. (See for a more thorough discussion of log
file handling.)
TCP/IP
The postmaster also takes a number of other command line options. For
more information, see the reference page and below. In particular, in order for the
server to accept TCP/IP connections (rather than just Unix domain
socket ones), you must specify the option.
pg_ctl
This shell syntax can get tedious quickly. Therefore the shell
script wrapper pg_ctl is provided to
simplify some tasks. For example:
pg_ctl start -l logfile
will start the server in the background and put the output into the
named log file. The option has the same meaning
here as in the postmaster. pg_ctl is also
capable of stopping the server.
Normally, you will want to start the database server when the
computer boots. Auto-start scripts are operating-system specific.
There are a few distributed with
PostgreSQL in the
/contrib/start-scripts> directory. This may require root
privileges.
Different systems have different conventions for starting up daemons
at boot time. Many systems have a file
/etc/rc.local or
/etc/rc.d/rc.local. Others use
rc.d> directories. Whatever you do, the server must be
run by the PostgreSQL user account
and not by root or any other user. Therefore you
probably should form your commands using su -c '...'
postgres. For example:
su -c 'pg_ctl start -D /usr/local/pgsql/data -l serverlog' postgres
Here are a few more operating system specific suggestions. (Always
replace these with the proper installation directory and the user
name.)
For FreeBSD, look at the file
contrib/start-scripts/freebsd in the
PostgreSQL source distribution.
FreeBSD>>
On OpenBSD, add the following lines
to the file /etc/rc.local:
OpenBSD>>
if [ -x /usr/local/pgsql/bin/pg_ctl -a -x /usr/local/pgsql/bin/postmaster ]; then
su - -c '/usr/local/pgsql/bin/pg_ctl start -l /var/postgresql/log -s' postgres
echo -n ' postgresql'
fi
On Linux systems either add
Linux>>
/usr/local/pgsql/bin/pg_ctl start -l logfile -D /usr/local/pgsql/data
to /etc/rc.d/rc.local or look at the file
contrib/start-scripts/linux in the
PostgreSQL source distribution.
On NetBSD, either use the
FreeBSD or
Linux start scripts, depending on
preference. NetBSD>>
On Solaris, create a file called
/etc/init.d/postgresql which should contain
the following line:
Solaris>>
su - postgres -c "/usr/local/pgsql/bin/pg_ctl start -l logfile -D /usr/local/pgsql/data"
Then, create a symbolic link to it in /etc/rc3.d> as
S99postgresql>.
While the postmaster is running, its
PID is in the file
postmaster.pid in the data directory. This is
used to prevent multiple postmasters running in the same data
directory, and can also be used for shutting down the postmaster.
Server Start-up Failures
There are several common reasons the postmaster might fail to
start. Check the postmaster's log file, or start it by hand
(without redirecting standard output or standard error) and see
what error messages appear. Some of the error messages are
self-explanatory, but some are not, as shown below:
FATAL: StreamServerPort: bind() failed: Address already in use
Is another postmaster already running on that port?
This usually means just what it suggests: you tried to start
another postmaster on the same port where one is already running.
However, if the kernel error message is not Address
already in use or some variant of that, there may
be a different problem. For example, trying to start a postmaster
on a reserved port number may draw something like:
$ postmaster -i -p 666
FATAL: StreamServerPort: bind() failed: Permission denied
Is another postmaster already running on that port?
A message like:
IpcMemoryCreate: shmget(key=5440001, size=83918612, 01600) failed: Invalid argument
FATAL 1: ShmemCreate: cannot create region
probably means your kernel's limit on the size of shared memory is
smaller than the buffer area PostgreSQL
is trying to create (83918612 bytes in this example). Or it could
mean that you don't have System-V-style shared memory support
configured into your kernel at all. As a temporary workaround, you
can try starting the postmaster with a smaller-than-normal number
of buffers ( switch). You will eventually want
to reconfigure your kernel to increase the allowed shared memory
size. You may see this message when trying to start multiple
postmasters on the same machine if their total space requested
exceeds the kernel limit.
An error like:
IpcSemaphoreCreate: semget(key=5440026, num=16, 01600) failed: No space left on device
does not mean you've run out of disk space. It
means your kernel's limit on the number of System V semaphores is
smaller than the number PostgreSQL wants
to create. As above, you may be able to work around the problem by
starting the postmaster with a reduced number of backend processes
( switch), but you'll eventually want to
increase the kernel limit.
If you get an illegal system call> error, it is likely
shared memory or semaphores are not supported in your kernel at
all. In that case your only option is to reconfigure the kernel to
enable these features.
Details about configuring System V>
IPC> facilities are given in .
Client Connection Problems
Although the error conditions possible on the client side are quite
varied and application-dependent, a few of them might be directly
related to how the server was started up. Conditions other than
those shown below should be documented with the respective client
application.
psql: could not connect to server: Connection refused
Is the server running on host server.joe.com and accepting
TCP/IP connections on port 5432?
This is the generic I couldn't find a server to talk
to failure. It looks like the above when TCP/IP
communication is attempted. A common mistake is to forget the
option to allow the postmaster to accept TCP/IP
connections.
Alternatively, you'll get this when attempting Unix-socket
communication to a local postmaster:
psql: could not connect to server: Connection refused
Is the server running locally and accepting
connections on Unix domain socket "/tmp/.s.PGSQL.5432"?
The last line is useful in verifying that the client is trying to
connect to the right place. If there is in fact no postmaster
running there, the kernel error message will typically be either
Connection refused or
No such file or directory, as
illustrated. (It is important to realize that
Connection refused in this context
does not mean that the postmaster got your
connection request and rejected it -- that case will produce a
different message, as shown in .) Other error messages
such as Connection timed out may
indicate more fundamental problems, like lack of network
connectivity.
Run-time configurationconfigurationserver
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
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.
SIGHUP
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 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.
Planner and Optimizer TuningCPU_INDEX_TUPLE_COST (floating point)
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.
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.
index scanENABLE_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.
sequential scanENABLE_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.
genetic query optimizationGEQOgenetic query optimizationGEQO (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.
GEQO_EFFORT (integer)GEQO_GENERATIONS (integer)GEQO_POOL_SIZE (integer)GEQO_RANDOM_SEED (integer)GEQO_SELECTION_BIAS (floating point)
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.
KSQO (boolean)
The Key Set Query Optimizer
(KSQO) causes the query planner to convert
queries whose WHERE> clause contains many OR'ed AND
clauses (such as WHERE (a=1 AND b=2) OR (a=2 AND b=3)
...) into a union query. This method can be faster
than the default implementation, but it doesn't necessarily give
exactly the same results, since UNION> implicitly
adds a SELECT DISTINCT> clause to eliminate identical
output rows. KSQO is commonly used when
working with products like Microsoft
Access, which tend to generate queries of this
form.
The KSQO algorithm used to be absolutely
essential for queries with many OR'ed AND clauses, but in
PostgreSQL 7.0 and later the standard
planner handles these queries fairly successfully; hence the
default is off.
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.
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.
Logging and DebuggingSERVER_MIN_MESSAGES (string)
This controls how much detail is written to the server logs. The
default is NOTICE>. Valid values are DEBUG5>,
DEBUG4>, DEBUG3>, DEBUG2>,
DEBUG1>, INFO>, NOTICE>,
WARNING>, ERROR>, LOG>,
FATAL>, and PANIC>. Later values send less
detail to the logs. LOG> has a different precedence
here than in CLIENT_MIN_MESSAGES>.
CLIENT_MIN_MESSAGES (string)
This controls how much detail is written to the client. The
default is NOTICE>. Valid values are
DEBUG5>, DEBUG4>, DEBUG3>,
DEBUG2>, DEBUG1>, LOG>,
NOTICE>, WARNING>, and ERROR>.
Later values send less information to the user. LOG>
has a different precedence here than in
SERVER_MIN_MESSAGES>.
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 (see the configure option
--enable-cassert). Note that
DEBUG_ASSERTIONS defaults to on if
PostgreSQL has been built this way.
DEBUG_PRINT_QUERY (boolean)DEBUG_PRINT_PARSE (boolean)DEBUG_PRINT_REWRITTEN (boolean)DEBUG_PRINT_PLAN (boolean)DEBUG_PRETTY_PRINT (boolean)
These flags enable various debugging output to be sent to the
server log. For each executed query, prints either the query text,
the resulting parse tree, the query rewriter output, or the execution
plan. indents these displays
to produce a more readable but much longer output format.
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_PID (boolean)
Prefixes each server log message with the process ID of the
backend process. This is useful to sort out which messages
pertain to which connection. The default is off.
LOG_TIMESTAMP (boolean)
Prefixes each server log message with a time stamp. The default
is off.
SHOW_QUERY_STATS (boolean)SHOW_PARSER_STATS (boolean)SHOW_PLANNER_STATS (boolean)SHOW_EXECUTOR_STATS (boolean)
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.
STATS_COMMAND_STRING (boolean)STATS_BLOCK_LEVEL (boolean)STATS_ROW_LEVEL (boolean)
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.
To use syslog>, the build of
PostgreSQL must be configured with
the option.
SYSLOG_FACILITY (string)
This option determines the syslogfacility 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.
General operationAUSTRALIAN_TIMEZONES (bool)Australian time zones>>
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)timeout>authentication>
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.
deadlocktimeouttimeoutdeadlockDEADLOCK_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.
transaction isolation levelDEFAULT_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.
Consult the PostgreSQL User's Guide and
the command SET TRANSACTION for more
information.
DYNAMIC_LIBRARY_PATH (string)dynamic_library_path>>
dynamic loading>>
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 $libdir, the
compiled-in PostgreSQL package
library directory is substituted. This where the modules
provided by the PostgreSQL
distribution are installed. (Use pg_config
--pkglibdir to print the name of this directory.) For
example:
dynamic_library_path = '/usr/local/lib/postgresql:/home/my_project/lib:$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.
fsyncFSYNC (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
fsync>s is considerably less in
PostgreSQL> version 7.1 and later. If you
previously suppressed fsync>s 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.
KRB_SERVER_KEYFILE (string)
Sets the location of the Kerberos server key file. See
for details.
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 off (do not encrypt the password), but
this choice may change in a future release.
PORT (integer)port>>
The TCP port the server listens on; 5432 by default. This
option can only be set at server start.
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 postmaster silently. If this option is set, the postmaster
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 512 kilobytes. Note that
for a complex query, several sorts and/or hashes 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.
SQL_INHERITANCE (bool)inheritance>>
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 User's
Guide for more information about inheritance.
SSLSSL (boolean)
Enables SSL> connections. Please read
before using this. The default
is off.
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.
TRANSFORM_NULL_EQUALS (boolean)IS NULL>>
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
NULLs, 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 NULL (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, 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.
Refer to the User's Guide for related
information.
UNIX_SOCKET_DIRECTORY (string)
Specifies the directory of the Unix-domain socket on which the
postmaster 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
postmaster.) In combination with the option
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
) and 0700
(only user). (Note that actually for a Unix 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 .
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>).
WAL
See also for details on WAL
tuning.
CHECKPOINT_SEGMENTS (integer)
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 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 non-zero, turn on WAL-related debugging output on standard
error.
WAL_FILES (integer)
Number of log files that are created in advance at checkpoint
time. This option can only be set at server start or in the
postgresql.conf file.
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.
Short options
For convenience there are also single letter option switches
available for many parameters. They are described in the following
table.
For historical reasons, options marked * must be
passed to the individual backend process via the
postmaster option, for example,
$ postmaster -o '-S 1024 -s'
or via PGOPTIONS from the client side, as explained
above.
Managing Kernel Resources
A large PostgreSQL> installation can quickly exhaust
various operating system resource limits. (On some systems, the
factory defaults are so low that you don't even need a really
large> installation.) If you have encountered this kind of
problem, keep reading.
Shared Memory and Semaphoresshared memorysemaphores
Shared memory and semaphores are collectively referred to as
System V>
IPC> (together with message queues, which are not
relevant for PostgreSQL>). Almost all modern
operating systems provide these features, but not all of them have
them turned on or sufficiently sized by default, especially systems
with BSD heritage. (For the QNX> and
BeOS> ports, PostgreSQL>
provides its own replacement implementation of these facilities.)
The complete lack of these facilities is usually manifested by an
Illegal system call> error upon postmaster start. In
that case there's nothing left to do but to reconfigure your
kernel -- PostgreSQL> won't work without them.
When PostgreSQL> exceeds one of the various hard
IPC> limits, the postmaster will refuse to start and
should leave an instructive error message describing the problem
encountered and what to do about it. (See also .) The relevant kernel
parameters are named consistently across different systems; gives an overview. The methods to set
them, however, vary. Suggestions for some platforms are given below.
Be warned that it is often necessary to reboot your machine, and
possibly even recompile the kernel, to change these settings.
System V> IPC> parameters>
Name>
Description>
Reasonable values>
SHMMAX>>
Maximum size of shared memory segment (bytes)>
250kB + 8.2kB * shared_buffers> + 14.2kB * max_connections> or infinitySHMMIN>>
Minimum size of shared memory segment (bytes)>
1>
SHMALL>>
Total amount of shared memory available (bytes or pages)>
if bytes, same as SHMMAX; if pages, ceil(SHMMAX/PAGE_SIZE)>
SHMSEG>>
Maximum number of shared memory segments per process>
only 1 segment is needed, but the default is much higher>
SHMMNI>>
Maximum number of shared memory segments system-wide>
like SHMSEG> plus room for other applications>
SEMMNI>>
Maximum number of semaphore identifiers (i.e., sets)>
>= ceil(max_connections / 16)>
SEMMNS>>
Maximum number of semaphores system-wide>
ceil(max_connections / 16) * 17 + room for other applications>
SEMMSL>>
Maximum number of semaphores per set>
>= 17>
SEMMAP>>
Number of entries in semaphore map>
see text>
SEMVMX>>
Maximum value of semaphore>
>= 255 (The default is often 32767, don't change unless asked to.)>
SHMMAX The most important
shared memory parameter is SHMMAX>, the maximum size, in
bytes, of a shared memory segment. If you get an error message from
shmget> like Invalid argument>, it is
possible that this limit has been exceeded. The size of the required
shared memory segment varies both with the number of requested
buffers (
Less likely to cause problems is the minimum size for shared
memory segments (SHMMIN>), which should be at most
approximately 256 kB for PostgreSQL> (it is
usually just 1). The maximum number of segments system-wide
(SHMMNI>) or per-process (SHMSEG>) should
not cause a problem unless your system has them set to zero. Some
systems also have a limit on the total amount of shared memory in
the system; see the platform-specific instructions below.
PostgreSQL> uses one semaphore per allowed connection
(
In some cases it might also be necessary to increase
SEMMAP> to be at least on the order of
SEMMNS>. This parameter defines the size of the semaphore
resource map, in which each contiguous block of available semaphores
needs an entry. When a semaphore set is freed it is either added to
an existing entry that is adjacent to the freed block or it is
registered under a new map entry. If the map is full, the freed
semaphores get lost (until reboot). Fragmentation of the semaphore
space could over time lead to fewer available semaphores than there
should be.
The SEMMSL> parameter, which determines how many
semaphores can be in a set, must be at least 17 for
PostgreSQL>.
Various other settings related to semaphore undo>, such as
SEMMNU> and SEMUME>, are not of concern
for PostgreSQL>.
BSD/OS>BSD/OS>>
Shared Memory>
By default, only 4 MB of shared memory is supported. Keep in
mind that shared memory is not pageable; it is locked in RAM.
To increase the number of shared buffers supported by the
postmaster, add the following to your kernel configuration
file. A SHMALL> value of 1024 represents 4MB of
shared memory. The following increases the maximum shared
memory area to 32 MB:
options "SHMALL=8192"
options "SHMMAX=\(SHMALL*PAGE_SIZE\)"
For those running 4.1 or later, just make the above changes,
recompile the kernel, and reboot. For those running earlier
releases, use bpatch> to find the
sysptsize> value in the current kernel. This is
computed dynamically at boot time.
$ bpatch -r sysptsize>
0x9 = 9>
Next, add SYSPTSIZE> as a hard-coded value in the
kernel configuration file. Increase the value you found using
bpatch>. Add 1 for every additional 4 MB of
shared memory you desire.
options "SYSPTSIZE=16"
sysptsize> cannot be changed by sysctl.
Semaphores>
You may need to increase the number of semaphores. By default,
PostgreSQL> allocates 34 semaphores, which is
over half the default system total of 60.
Set the values you want in your kernel configuration file, e.g.:
options "SEMMNI=40"
options "SEMMNS=240"
options "SEMUME=40"
options "SEMMNU=120"
FreeBSD>NetBSD>OpenBSD>FreeBSD>>
NetBSD>>
OpenBSD>>
The options SYSVSHM> and SYSVSEM> need
to be enabled when the kernel is compiled. (They are by
default.) The maximum size of shared memory is determined by
the option SHMMAXPGS> (in pages). The following
shows an example of how to set the various parameters:
options SYSVSHM
options SHMMAXPGS=4096
options SHMSEG=256
options SYSVSEM
options SEMMNI=256
options SEMMNS=512
options SEMMNU=256
options SEMMAP=256
(On NetBSD> and OpenBSD> the key word is actually
option singular.)
You may also want to use the sysctl> setting to
lock shared memory into RAM and prevent it from being paged out
to swap.
HP-UX>HP-UX>>
The default settings tend to suffice for normal installations.
On HP-UX> 10, the factory default for
SEMMNS> is 128, which might be too low for larger
database sites.
IPC> parameters can be set in the System
Administration Manager> (SAM>) under
Kernel
Configuration>Configurable Parameters>>. Hit
Create A New Kernel> when you're done.
Linux>Linux>>
The default shared memory limit (both
SHMMAX and SHMALL) is 32
MB in 2.2 kernels, but it can be changed in the
proc file system (without reboot). For
example, to allow 128 MB:
$echo 134217728 >/proc/sys/kernel/shmall$echo 134217728 >/proc/sys/kernel/shmmax
You could put these commands into a script run at boot-time.
Alternatively, you can use
sysctl8, if available, to
control these parameters. Look for a file called
/etc/sysctl.conf and add lines like the
following to it:
kernel.shmall = 134217728
kernel.shmmax = 134217728
This file is usually processed at boot time, but
sysctl can also be called
explicitly later.
Other parameters are sufficiently sized for any application. If
you want to see for yourself look in
/usr/src/linux/include/asm-xxx>/shmpara
m.h> and /usr/src/linux/include/linux/sem.h>.
SCO OpenServer>SCO OpenServer>>
In the default configuration, only 512 kB of shared memory per
segment is allowed, which is about enough for Solaris>Solaris>>
At least in version 2.6, the default maximum size of a shared
memory segments is too low for PostgreSQL>. The
relevant settings can be changed in /etc/system>,
for example:
set shmsys:shminfo_shmmax=0x2000000
set shmsys:shminfo_shmmin=1
set shmsys:shminfo_shmmni=256
set shmsys:shminfo_shmseg=256
set semsys:seminfo_semmap=256
set semsys:seminfo_semmni=512
set semsys:seminfo_semmns=512
set semsys:seminfo_semmsl=32
You need to reboot for the changes to take effect.
See also >
for information on shared memory under
Solaris>.
UnixWare>UnixWare>>
On UnixWare> 7, the maximum size for shared
memory segments is 512 kB in the default configuration. This
is enough for about Resource Limits
Unix-like operating systems enforce various kinds of resource limits
that might interfere with the operation of your
PostgreSQL server. Of particular
importance are limits on the number of processes per user, the
number of open files per process, and the amount of memory available
to each process. Each of these have a hard and a
soft limit. The soft limit is what actually counts
but it can be changed by the user up to the hard limit. The hard
limit can only be changed by the root user. The system call
setrlimit is responsible for setting these
parameters. The shell's built-in command ulimit
(Bourne shells) or limit (csh>) is
used to control the resource limits from the command line. On
BSD-derived systems the file /etc/login.conf
controls the various resource limits set during login. See
login.conf5 for details. The relevant
parameters are maxproc,
openfiles, and datasize. For
example:
default:\
...
:datasize-cur=256M:\
:maxproc-cur=256:\
:openfiles-cur=256:\
...
(-cur is the soft limit. Append
-max to set the hard limit.)
Kernels can also have system-wide limits on some resources.
On Linux/proc/sys/fs/file-max determines the
maximum number of open files that the kernel will support. It can
be changed by writing a different number into the file or by
adding an assignment in /etc/sysctl.conf.
The maximum limit of files per process is fixed at the time the
kernel is compiled; see
/usr/src/linux/Documentation/proc.txt for
more information.
The PostgreSQL server uses one process
per connection so you should provide for at least as many processes
as allowed connections, in addition to what you need for the rest
of your system. This is usually not a problem but if you run
several servers on one machine things might get tight.
The factory default limit on open files is often set to
socially friendly values that allow many users to
coexist on a machine without using an inappropriate fraction of
the system resources. If you run many servers on a machine this
is perhaps what you want, but on dedicated servers you may want to
raise this limit.
On the other side of the coin, some systems allow individual
processes to open large numbers of files; if more than a few
processes do so then the system-wide limit can easily be exceeded.
If you find this happening, and don't want to alter the system-wide
limit, you can set PostgreSQL's
max_files_per_process configuration parameter to
limit the consumption of open files.
Shutting down the server
There are several ways to shut down the database server. You control
the type of shutdown by sending different signals to the server
process.
SIGTERM
After receiving SIGTERM, the postmaster
disallows new connections, but lets existing backends end their
work normally. It shuts down only after all of the backends
terminate normally. This is Smart
Shutdown.
SIGINT
The postmaster disallows new connections and sends all existing
backends SIGTERM, which will cause them
to abort their current transactions and exit promptly. It then
waits for the backends to exit and finally shuts down. This is
Fast Shutdown.
SIGQUIT This is Immediate Shutdown, which
will cause the postmaster to send a
SIGQUIT to all backends and exit
immediately (without properly shutting itself down). The backends
likewise exit immediately upon receiving
SIGQUIT. This will lead to recovery (by
replaying the WAL log) upon next start-up. This is recommended
only in emergencies.
It is best not to use SIGKILL to shut down
the postmaster. This will prevent the postmaster from releasing
shared memory and semaphores, which may then have to be done by
manually.
The PID> of the postmaster process can be found using the
ps program, or from the file
postmaster.pid in the data directory. So for
example, to do a fast shutdown:
$ kill -INT `head -1 /usr/local/pgsql/data/postmaster.pid`
The program pg_ctl is a shell script
that provides a more convenient interface for shutting down the
postmaster.
Secure TCP/IP Connections with SSLSSLPostgreSQL> has native support for using
SSL> connections to encrypt client/server communications
for increased security. This requires
OpenSSL be installed on both client and
server systems and support enabled at build time (see ).
With SSL support compiled in, the PostgreSQL> server
can be started with the argument
The server will listen for both standard and SSL connections on the
same TCP/IP port, and will negotiate with any connecting client on
whether to use SSL. See about
how to force the server to only use of SSL for certain connections.
For details on how to create your server private key and certificate,
refer to the OpenSSL> documentation. A simple
self-signed certificate can be used to get started for testing, but a
certificate signed by a CA> (either one of the global
CAs> or a local one) should be used in production so the
client can verify the server's identity. To create a quick
self-signed certificate, use the following
OpenSSL command:
openssl req -new -text -out cert.req
Fill out the information that openssl> asks for. Make sure
that you enter the local host name as Common Name; the challenge
password can be left blank. The script will generate a key that is
passphrase protected; it will not accept a pass phrase that is less
than four characters long. To remove the passphrase (as you must if
you want automatic start-up of the server), run the commands
openssl rsa -in privkey.pem -out cert.pem
Enter the old passphrase to unlock the existing key. Now do
openssl req -x509 -in cert.req -text -key cert.pem -out cert.cert
cp cert.pem $PGDATA/server.key
cp cert.cert $PGDATA/server.crt
to turn the certificate into a self-signed certificate and to copy the
key and certificate to where the server will look for them.
Secure TCP/IP Connections with SSH tunnelssshAcknowledgement
Idea taken from an email by Gene Selkov, Jr.
(selkovjr@mcs.anl.gov>) written on 1999-09-08 in response
to a question from Eric Marsden.
One can use ssh to encrypt the network
connection between clients and a
PostgreSQL server. Done properly, this
should lead to an adequately secure network connection.
First make sure that an ssh server is
running properly on the same machine as
PostgreSQL and that you can log in using
ssh as some user. Then you can establish a secure
tunnel with a command like this from the client machine:
$ ssh -L 3333:foo.com:5432 joe@foo.com
The first number in the argument, 3333, is the
port number of your end of the tunnel; it can be chosen freely. The
second number, 5432, is the remote end of the tunnel -- the port
number your server is using. The name or the address in between
the port numbers is the host with the database server you are going
to connect to. In order to connect to the database server using
this tunnel, you connect to port 3333 on the local machine:
psql -h localhost -p 3333 template1
To the database server it will then look as though you are really
user joe@foo.com and it will use whatever
authentication procedure was set up for this user. In order for the
tunnel setup to succeed you must be allowed to connect via
ssh as joe@foo.com, just
as if you had attempted to use ssh to set up a
terminal session.
Several other products exist that can provide secure tunnels using
a procedure similar in concept to the one just described.