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.
+
PostgreSQL can sometimes exhaust various operating system+ resource limits, especially when multiple copies of the server are running
+ on the same system, or in very large installations. This section explains
+ the kernel resources used by
PostgreSQL and the steps you+ can take to resolve problems related to kernel resource consumption.
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 many of them don't have
- them turned on or sufficiently sized by default, especially as
- available RAM and the demands of database applications grow.
- (On Windows,
-
PostgreSQL provides its own replacement- implementation of these facilities, so most of this section
- can be disregarded.)
+ relevant for
PostgreSQL). Except on+
Windows, where PostgreSQL+ provides its own replacement implementation of these facilities, these
+ facilities are required in order to run
them, however, vary. Suggestions for some platforms are given below.
+
+ Prior to
PostgreSQL 9.3, the amount of System V shared+ memory required to start the server was much larger. If you are running
+ an older version of the server, please consult the documentation for
+ your server version.
+
+
<systemitem class="osname">System V</> <acronym>IPC</> Parameters
|
SHMMAX
Maximum size of shared memory segment (bytes)
- at least several megabytes (see text)
+ at least 1kB (more if running many copies of the server)
|
-
-
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
- likely that this limit has been exceeded. The size of the required
- shared memory segment varies depending on several
-
PostgreSQL configuration parameters, as shown in- . (Any error message you might
- get will include the exact size of the failed allocation request.)
- You can, as a temporary solution, lower some of those settings to
- avoid the failure. While it is possible to get
-
PostgreSQL to run with SHMMAX as small as- 2 MB, you need considerably more for acceptable performance. Desirable
- settings are in the hundreds of megabytes to a few gigabytes.
-
-
- Some systems also have a limit on the total amount of shared memory in
- the system (SHMALL). Make sure this is large enough
- for
PostgreSQL plus any other applications that- are using shared memory segments. Note that SHMALL
- is measured in pages rather than bytes on many systems.
+
PostgreSQL requires a few bytes of System V shared memory+ (typically 48 bytes, on 64-bit platforms) for each copy of the server.
+ On most modern operating systems, this amount can easily be allocated.
+ However, if you are running many copies of the server, or if other
+ applications are also using System V shared memory, it may be necessary
+ to increase SHMMAX, the maximum size in bytes of a shared
+ memory segment, or SHMALL, the total amount of System V shared
+ memory system-wide. Note that SHMALL is measured in pages
+ rather than bytes on many systems.
Less likely to cause problems is the minimum size for shared
memory segments (SHMMIN), which should be at most
- approximately
500 kB for
PostgreSQL (it is+ approximately
32 bytes for
PostgreSQL (it is usually just 1). The maximum number of segments system-wide
(SHMMNI) or per-process (SHMSEG) are unlikely
to cause a problem unless your system has them set to zero.
- The default settings are only suitable for small installations
- (for example, default SHMMAX is 32
- MB). Changes can be made via the sysctl or
+ The default settings can be changed using
+ the sysctl or
loader interfaces. The following
parameters can be set using sysctl:
- The default maximum segment size is 32 MB, which is only adequate
- for very small
PostgreSQL- installations. The default maximum total size is 2097152
+ The default maximum segment size is 32 MB, and the
+ default maximum total size is 2097152
pages. A page is almost always 4096 bytes except in unusual
kernel configurations with huge pages
- (use getconf PAGE_SIZE to verify). That
- makes a default limit of 8 GB, which is often enough, but not
- always.
+ (use getconf PAGE_SIZE to verify).
- The default maximum size of a shared memory segment is too low for
-
PostgreSQL. The relevant settings can be changed in+ The relevant settings can be changed in
/etc/system, for example:
set shmsys:shminfo_shmmax=0x2000000
In Solaris 10 and OpenSolaris, the default shared memory and
semaphore settings are good enough for most
PostgreSQL applications. Solaris now defaults
- to a
SHMMAX of one-quarter of system RAM. If- you need to increase this in order to set shared memory settings
- slightly higher, you should use a project setting associated
+ to a
SHMMAX of one-quarter of system RAM.+ To further adjust this setting, use a project setting associated
with the postgres user. For example, run the
following as root:
This command adds the user.postgres project and
- raises the shared memory maximum for the postgres
+ sets the shared memory maximum for the postgres
user to 8GB, and takes effect the next time that user logs
in, or when you restart
PostgreSQL (not reload). The above assumes that
PostgreSQL is run by
On
UnixWare 7, the maximum size for shared- memory segments is only 512 kB in the default configuration.
+ memory segments is 512 kB in the default configuration.
To display the current value of SHMMAX, run:
/etc/conf/bin/idtune -g SHMMAX
-
-
<productname>PostgreSQL</productname> Shared Memory Usage</></div>
<div class="diff rem">-</div>
<div class="diff rem">- <tgroup cols="2"></div>
<div class="diff rem">- <thead></div>
<div class="diff rem">- <row></div>
<div class="diff rem">- <entry>Usage</></div>
<div class="diff rem">- <entry>Approximate shared memory bytes required (as of 8.3)</></div>
<div class="diff rem">- </row></div>
<div class="diff rem">- </thead></div>
<div class="diff rem">-</div>
<div class="diff rem">- <tbody></div>
<div class="diff rem">- <row></div>
<div class="diff rem">- <entry>Connections</></div>
<div class="diff rem">- <entry>(1800 + 270 * <xref</div>
<div class="diff rem">- linkend="guc-max-locks-per-transaction">) * <xref</div>
<div class="diff rem">- linkend="guc-max-connections"></entry></div>
<div class="diff rem">- </row></div>
<div class="diff rem">-</div>
<div class="diff rem">- <row></div>
<div class="diff rem">- <entry>Autovacuum workers</></div>
<div class="diff rem">- <entry>(1800 + 270 * <xref</div>
<div class="diff rem">- linkend="guc-max-locks-per-transaction">) * <xref</div>
<div class="diff rem">- linkend="guc-autovacuum-max-workers"></entry></div>
<div class="diff rem">- </row></div>
<div class="diff rem">-</div>
<div class="diff rem">- <row></div>
<div class="diff rem">- <entry>Prepared transactions</></div>
<div class="diff rem">- <entry>(770 + 270 * <xref</div>
<div class="diff rem">- linkend="guc-max-locks-per-transaction">) * <xref linkend="guc-max-prepared-transactions"></entry></div>
<div class="diff rem">- </row></div>
<div class="diff rem">-</div>
<div class="diff rem">- <row></div>
<div class="diff rem">- <entry>Shared disk buffers</></div>
<div class="diff rem">- <entry>(<xref linkend="guc-block-size"> + 208) * <xref linkend="guc-shared-buffers"></entry></div>
<div class="diff rem">- </row></div>
<div class="diff rem">-</div>
<div class="diff rem">- <row></div>
<div class="diff rem">- <entry>WAL buffers</></div>
<div class="diff rem">- <entry>(<xref linkend="guc-wal-block-size"> + 8) * <xref linkend="guc-wal-buffers"></entry></div>
<div class="diff rem">- </row></div>
<div class="diff rem">-</div>
<div class="diff rem">- <row></div>
<div class="diff rem">- <entry>Fixed space requirements</></div>
<div class="diff rem">- <entry>770 kB</entry></div>
<div class="diff rem">- </row></div>
<div class="diff rem">- </tbody></div>
<div class="diff rem">- </tgroup></div>
<div class="diff rem">- </table></div>
<div class="diff rem">-</div>
<div class="diff ctx"> </sect2></div>
<div class="diff ctx"> </div>
<div class="diff ctx"> <sect2></div>
</div>
</div>
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