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Shed some light onto SysV IPC configuration.

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This commit is contained in:
Peter Eisentraut
2000-07-22 14:49:01 +00:00
parent 100dd889d6
commit ef2a6b8b83
2 changed files with 510 additions and 32 deletions
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462
doc/src/sgml/runtime.sgml
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@ -1,5 +1,5 @@
<!-- <!--
$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.16 2000/07/17 22:32:44 tgl Exp $ $Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.17 2000/07/22 14:49:00 petere Exp $
--> -->
<Chapter Id="runtime"> <Chapter Id="runtime">
@ -267,13 +267,13 @@ FATAL: StreamServerPort: bind() failed: Permission denied
<para> <para>
A message like A message like
<screen> <screen>
IpcMemoryCreate: shmget(5440001, 83918612, 01600) failed: Invalid argument IpcMemoryCreate: shmget(key=5440001, size=83918612, 01600) failed: Invalid argument
FATAL 1: ShmemCreate: cannot create region FATAL 1: ShmemCreate: cannot create region
</screen> </screen>
probably means that your kernel's limit on the size of shared probably means that your kernel's limit on the size of shared
memory areas is smaller than the buffer area that Postgres is memory areas is smaller than the buffer area that Postgres is
trying to create (83918612 bytes in this example). Or it could trying to create (83918612 bytes in this example). Or it could
mean that you don't have SysV-style shared memory support mean that you don't have System-V-style shared memory support
configured into your kernel at all. As a temporary workaround, configured into your kernel at all. As a temporary workaround,
you can try starting the postmaster with a smaller-than-normal you can try starting the postmaster with a smaller-than-normal
number of buffers (<option>-B</option> switch). You will number of buffers (<option>-B</option> switch). You will
@ -286,17 +286,22 @@ FATAL 1: ShmemCreate: cannot create region
<para> <para>
An error like An error like
<screen> <screen>
IpcSemaphoreCreate: semget(5440026, 16, 0600) failed: No space left on device IpcSemaphoreCreate: semget(key=5440026, num=16, 01600) failed: No space left on device
</screen> </screen>
does <emphasis>not</emphasis> mean that you've run out of disk does <emphasis>not</emphasis> mean that you've run out of disk
space; it means that your kernel's limit on the number of SysV space; it means that your kernel's limit on the number of System
semaphores is smaller than the number V semaphores is smaller than the number
<productname>Postgres</productname> wants to create. As above, <productname>Postgres</productname> wants to create. As above,
you may be able to work around the problem by starting the you may be able to work around the problem by starting the
postmaster with a reduced number of backend processes postmaster with a reduced number of backend processes
(<option>-N</option> switch), but you'll eventually want to (<option>-N</option> switch), but you'll eventually want to
increase the kernel limit. increase the kernel limit.
</para> </para>
<para>
Details about configuring System V IPC facilities are given in
<xref linkend="sysvipc">.
</para>
</sect2> </sect2>
<sect2 id="client-connection-problems"> <sect2 id="client-connection-problems">
@ -1073,6 +1078,445 @@ env PGOPTIONS='--geqo=off' psql
</sect1> </sect1>
<sect1 id="kernel-resources">
<title>Managing Kernel Resources</title>
<para>
A large <productname>Postgres</> installation can quickly hit
various operating system resource limits. (On some systems, the
factory defaults are so low that you don't even need a really
<quote>large</> installation.) If you have encountered this kind of
problem then keep reading.
</para>
<sect2 id="sysvipc">
<title>Shared Memory and Semaphores</title>
<para>
Shared memory and semaphores are collectively referred to as
<quote>System V IPC</> (together with message queues, which are
not relevant for <productname>Postgres</>). 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 port,
<productname>Postgres</> provides its own replacement
implementation of these facilities.)
</para>
<para>
The complete lack of these facilities is usually manifested by an
<errorname>Illegal system call</> error upon postmaster start. In
that case there's nothing left to do but to reconfigure your
kernel -- <productname>Postgres</> won't work without them.
</para>
<para>
When <productname>Postgres</> exceeds one of the various hard
limits of the IPC resources then the postmaster will refuse to
start up and should leave a marginally instructive error message
about which problem was encountered and what needs to be done
about it. The relevant kernel parameters have a relatively
consistent nomenclature across systems; <xref
linkend="sysvipc-parameters"> gives an overview. The methods to
set them, however, vary; suggestions for some platforms are given
below. Be aware, however, that you will have to reboot your
machine at best, or possibly recompile the kernel, to change these
settings.
</para>
<table id="sysvipc-parameters">
<title>System V IPC parameters</>
<tgroup cols="3">
<thead>
<row>
<entry>Name</>
<entry>Description</>
<entry>Reasonable values</>
</row>
</thead>
<tbody>
<row>
<entry><varname>SHMMAX</></>
<entry>Maximum size of shared memory segment (bytes)</>
<entry>512 kB + 8192 * buffers + extra ... infinity</entry>
</row>
<row>
<entry><varname>SHMMIN</></>
<entry>Minimum size of shared memory segment (bytes)</>
<entry>1 (at most 144)</>
</row>
<row>
<entry><varname>SHMSEG</></>
<entry>Maximum number of shared memory segments per process</>
<entry>Must be at least 3, but the default is much higher.</>
</row>
<row>
<entry><varname>SHMMNI</></>
<entry>Maximum number of shared memory segments system-wide</>
<entry>like <varname>SHMSEG</> + room for other applications</>
</row>
<row>
<entry><varname>SEMMNI</></>
<entry>Maximum number of semaphore identifiers (i.e., sets)</>
<entry>&gt;= ceil(max_connections % 16)</>
</row>
<row>
<entry><varname>SEMMNS</></>
<entry>Maximum number of semaphores system-wide</>
<entry>number of allowed connections, rounded up to multiple of 16</>
</row>
<row>
<entry><varname>SEMMSL</></>
<entry>Maximum number of semaphores per set</>
<entry>&gt;= 16</>
</row>
<row>
<entry><varname>SEMMAP</></>
<entry>Number of entries in semaphore map</>
<entry>see text</>
</row>
<row>
<entry><varname>SEMVMX</></>
<entry>Maximum value of semaphore</>
<entry>&gt;= 255 (The default is often 32767, don't change unless asked to.)</>
</row>
</tbody>
</tgroup>
</table>
<para>
The most important shared memory parameter is <varname>SHMMAX</>,
the maximum size, in bytes, that a shared memory segment can have.
If you get an error message from <function>shmget</> along the
lines of <errorname>Invalid argument</> then it is possible that
this limit has been exceeded. The size of the required shared
memory segments varies both with the number of requested buffers
(<option>-B</> option) and the number of allowed connections
(<option>-N</> option), although the former is the dominant item.
(You can therefore, as a temporary solution, lower these settings
to get rid of the failures.) As a rough approximation you can
estimate the required segment size as the number of buffers times
the block size (8192 kB by default) plus ample overhead (at least
half a megabyte). Any error message you might get will contain the
size of the failed allocation. (<productname>Postgres</> will
actually use three shared memory segments, but the size of the
other two is negligible for this consideration.)
</para>
<para>
Less likely to cause problems is the minimum size for shared
memory segments (<varname>SHMMIN</>), which must be at least 144
for <productname>Postgres</> (it's usually just 1), and the
maximum number of segments system-wide (<varname>SHMMNI</>, as
mentioned, 3 are needed) or per-process (<varname>SHMSEG</>,
ditto). Some systems also have a limit on the total amount of
shared memory in the system; see the platform-specific
instructions below.
</para>
<para>
<productname>Postgres</> uses one semaphore per allowed connection
(<option>-N</> option), in sets of 16. The maximum number of
semaphores in the system is set by <varname>SEMMNS</>, which
consequently must be at least as high as the connection setting.
The parameter <varname>SEMMNI</> determines the limit on the
number of semaphore sets that can exist on the system at one time.
Hence this parameter must be at least
<literal>ceil(max_connections % 16)</>. Lowering the number of
allowed connections is a temporary workaround for failures, which
are usually confusingly worded <quote><errorname>No space left on
device</></>, from the function <function>semget()</>.
</para>
<para>
In some cases it might also turn out to be necessary to increase
<varname>SEMMAP</> to be at least on the order of
<varname>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 gets lost (until reboot). Fragmentation
of the semaphore space could therefore over time lead to less
available semaphores than there should be.
</para>
<para>
The <varname>SEMMSL</> parameter, which determines how many
semaphores can be in a set, must be at least 16 for
<productname>Postgres</>.
</para>
<para>
Various settings related to <quote>semaphore undo</>, such as
<varname>SEMMNU</> and <varname>SEMUME</>, are not of relevance
with <productname>Postgres</>.
</para>
<para>
<variablelist>
<varlistentry>
<term>BSD/OS</>
<listitem>
<formalpara>
<title>Shared Memory</>
<para>
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 buffers supported by the
postmaster, increase <varname>SHMMAXPGS</> by 1024 for every
additional 4 MB of shared memory:
<programlisting>
/sys/sys/shm.h:69:#define SHMMAXPGS 1024 /* max hardware pages... */
</programlisting>
The default setting of 1024 is for a maximum of 4 MB of shared
memory.
</para>
</formalpara>
<para>
For those running 4.1 or later, just recompile the kernel and
reboot. For those running earlier releases, use
<application>bpatch</> to find the <varname>sysptsize</> value
for the current kernel. This is computed dynamically at
bootup.
<screen>
$ <userinput>bpatch -r sysptsize</>
<computeroutput>0x9 = 9</>
</screen>
Next, change <varname>SYSPTSIZE</> to a hard-coded value. Use
the bpatch value, plus add 1 for every additional 4 MB of
shared memory you desire.
<programlisting>
/sys/i386/i386/i386_param.c:28:#define SYSPTSIZE 0 /* dynamically... */
</programlisting>
<varname>sysptsize</> can not be changed by sysctl on the fly.
</para>
<formalpara>
<title>Semaphores</>
<para>
You may need to increase the number of semaphores. By
default, <productname>Postgres</> allocates 32 semaphores,
one for each backend connection. This is just over half the
default system total of 60.
</para>
</formalpara>
<para>
The defaults are in <filename>/sys/sys/sem.h</>:
<programlisting>
/* Configuration parameters */
#ifndef SEMMNI
#define SEMMNI 10 /* # of semaphore identifiers */
#endif
#ifndef SEMMNS
#define SEMMNS 60 /* # of semaphores in system */
#endif
#ifndef SEMUME
#define SEMUME 10 /* max # of undo entries per process */
#endif
#ifndef SEMMNU
#define SEMMNU 30 /* # of undo structures in system */
#endif
</programlisting>
Set the values you want in your kernel config file, e.g.:
<programlisting>
options "SEMMNI=40"
options "SEMMNS=240"
options "SEMUME=40"
options "SEMMNU=120"
</programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>FreeBSD</>
<listitem>
<para>
The options <varname>SYSVSHM</> and <varname>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 <varname>SHMMAXPGS</> (in pages). The following
shows an example on how to set the various parameters:
<programlisting>
options SYSVSHM
options SHMMAXPGS=4096
options SHMSEG=256
options SYSVSEM
options SEMMNI=256
options SEMMNS=512
options SEMMNU=256
options SEMMAP=256
</programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>HPUX</>
<listitem>
<para>
The default settings tend to suffice for normal installations.
On <productname>HPUX</> 10, the factory default for
<varname>SEMMNS</> is 128, which might be too low for larger
database sites.
</para>
<para>
IPC parameters can be set in the <application>System
Administration Manager</> (<acronym>SAM</>) under
<menuchoice><guimenu>Kernel
Configuration</><guimenuitem>Configurable Parameters</></>.
Hit <guibutton>Create A New Kernel</> when you're done.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Linux</>
<listitem>
<para>
System V IPC is enabled by default and sufficiently sized for
most uses. The relevant parameters are in
<filename>/usr/src/linux/include/asm-<replaceable>xxx</>/shmparam.h</>
and <filename>/usr/src/linux/include/linux/sem.h</>. Be sure
to do <command>make dep</> before rebuilding the kernel.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>SCO OpenServer</>
<listitem>
<para>
In the default configuration, only 512 kB of shared memory per
segment is allowed, which is about enough for <option>-B 24 -N
12</>. To increase the setting, first change the directory to
<filename>/etc/conf/cf.d</>. To display the current value of
<varname>SHMMAX</>, in bytes, run
<programlisting>
./configure -y SHMMAX
</programlisting>
To set a new value for <varname>SHMMAX</>, run:
<programlisting>
./configure SHMMAX=<replaceable>value</>
</programlisting>
where <replaceable>value</> is the new value you want to use
(in bytes). After setting <varname>SHMMAX</>, rebuild the kernel
<programlisting>
./link_unix
</programlisting>
and reboot.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Solaris</>
<listitem>
<para>
At least in version 2.6, the maximum size of a shared memory
segment is set too low for <productname>Postgres</>. The
relevant settings can be changed in <filename>/etc/system</>,
for example:
<programlisting>
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
</programlisting>
You need to reboot to make the changes effective.
</para>
<para>
See also <ulink
url="http://www.sunworld.com/swol-09-1997/swol-09-insidesolaris.html">http://www.sunworld.com/swol-09-1997/swol-09-insidesolaris.html</>
for information on shared memory under
<productname>Solaris</>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>UnixWare</>
<listitem>
<para>
On <productname>UnixWare</> 7, the maximum size for shared
memory segments is 512 kB in the default configuration. This
is enough for about <option>-B 24 -N 12</>. To display the
current value of <varname>SHMMAX</>, run
<programlisting>
/etc/conf/bin/idtune -g SHMMAX
</programlisting>
which displays the current, default, minimum, and maximum
values, in bytes. To set a new value for <varname>SHMMAX</>,
run:
<programlisting>
/etc/conf/bin/idtune SHMMAX <replaceable>value</>
</programlisting>
where <replaceable>value</> is the new value you want to use
(in bytes). After setting <varname>SHMMAX</>, rebuild the
kernel
<programlisting>
/etc/conf/bin/idbuild -B
</programlisting>
and reboot.
</para>
</listitem>
</varlistentry>
</variablelist>
<note>
<para>
If your platform is not listed here, please consider
contributing some information.
</para>
</note>
</para>
</sect2>
<!--
Other fun things to write about one day:
* number of processes per user and system-wide (soft/hard limit)
* open files/inodes per user and system-wide (soft/hard limit)
(Think about this both ways: Increasing it to allow Postgres to
open more files, and decreasing it to prevent Postgres from taking
up all file descriptors.)
* stack and data segment size, plain-old memory limit
-->
</sect1>
<sect1 id="locale"> <sect1 id="locale">
<title>Locale Support</title> <title>Locale Support</title>
@ -1142,8 +1586,9 @@ postmaster -B 1024 -S -D/usr/local/pgsql/data/ -o '-Fe'
and if locale is broken <command>perl -v</> will complain and if locale is broken <command>perl -v</> will complain
something like: something like:
<screen> <screen>
8:17[mira]:~/WWW/postgres>setenv LC_CTYPE not_exist <prompt>$</> <userinput>export LC_CTYPE='not_exist'</>
8:18[mira]:~/WWW/postgres>perl -v <prompt>$</> <userinput>perl -v</>
<computeroutput>
perl: warning: Setting locale failed. perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings: perl: warning: Please check that your locale settings:
LC_ALL = (unset), LC_ALL = (unset),
@ -1151,6 +1596,7 @@ LC_CTYPE = "not_exist",
LANG = (unset) LANG = (unset)
are supported and installed on your system. are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C"). perl: warning: Falling back to the standard locale ("C").
</computeroutput>
</screen> </screen>
</para> </para>
</listitem> </listitem>

80
src/backend/storage/ipc/ipc.c
View File

@ -8,7 +8,7 @@
* *
* *
* IDENTIFICATION * IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/ipc/ipc.c,v 1.48 2000/05/31 00:28:29 petere Exp $ * $Header: /cvsroot/pgsql/src/backend/storage/ipc/ipc.c,v 1.49 2000/07/22 14:49:01 petere Exp $
* *
* NOTES * NOTES
* *
@ -54,7 +54,6 @@ bool proc_exit_inprogress = false;
static int UsePrivateMemory = 0; static int UsePrivateMemory = 0;
static void IpcMemoryDetach(int status, char *shmaddr); static void IpcMemoryDetach(int status, char *shmaddr);
static void IpcConfigTip(void);
/* ---------------------------------------------------------------- /* ----------------------------------------------------------------
* exit() handling stuff * exit() handling stuff
@ -241,7 +240,9 @@ IPCPrivateSemaphoreKill(int status,
union semun semun; union semun semun;
semun.val = 0; /* unused */ semun.val = 0; /* unused */
semctl(semId, 0, IPC_RMID, semun); if (semctl(semId, 0, IPC_RMID, semun) == -1)
elog(NOTICE, "IPCPrivateSemaphoreKill: semctl(%d, 0, IPC_RMID, ...) failed: %s",
semId, strerror(errno));
} }
@ -261,8 +262,8 @@ IPCPrivateMemoryKill(int status,
{ {
if (shmctl(shmId, IPC_RMID, (struct shmid_ds *) NULL) < 0) if (shmctl(shmId, IPC_RMID, (struct shmid_ds *) NULL) < 0)
{ {
elog(NOTICE, "IPCPrivateMemoryKill: shmctl(%d, %d, 0) failed: %m", elog(NOTICE, "IPCPrivateMemoryKill: shmctl(id=%d, IPC_RMID, NULL) failed: %m",
shmId, IPC_RMID); shmId);
} }
} }
} }
@ -307,10 +308,19 @@ IpcSemaphoreCreate(IpcSemaphoreKey semKey,
if (semId < 0) if (semId < 0)
{ {
fprintf(stderr, "IpcSemaphoreCreate: semget(%d, %d, 0%o) failed: %s\n", fprintf(stderr, "IpcSemaphoreCreate: semget(key=%d, num=%d, 0%o) failed: %s\n",
semKey, semNum, (unsigned)(permission|IPC_CREAT), semKey, semNum, (unsigned)(permission|IPC_CREAT),
strerror(errno)); strerror(errno));
IpcConfigTip();
if (errno == ENOSPC)
fprintf(stderr,
"\nThis error does *not* mean that you have run out of disk space.\n\n"
"It occurs either because system limit for the maximum number of\n"
"semaphore sets (SEMMNI), or the system wide maximum number of\n"
"semaphores (SEMMNS), would be exceeded. You need to raise the\n"
"respective kernel parameter. Look into the PostgreSQL documentation\n"
"for details.\n\n");
return (-1); return (-1);
} }
for (i = 0; i < semNum; i++) for (i = 0; i < semNum; i++)
@ -319,10 +329,16 @@ IpcSemaphoreCreate(IpcSemaphoreKey semKey,
errStatus = semctl(semId, 0, SETALL, semun); errStatus = semctl(semId, 0, SETALL, semun);
if (errStatus == -1) if (errStatus == -1)
{ {
fprintf(stderr, "IpcSemaphoreCreate: semctl(id=%d) failed: %s\n", fprintf(stderr, "IpcSemaphoreCreate: semctl(id=%d, 0, SETALL, ...) failed: %s\n",
semId, strerror(errno)); semId, strerror(errno));
if (errno == ERANGE)
fprintf(stderr,
"You possibly need to raise your kernel's SEMVMX value to be at least\n"
"%d. Look into the PostgreSQL documentation for details.\n",
semStartValue);
semctl(semId, 0, IPC_RMID, semun); semctl(semId, 0, IPC_RMID, semun);
IpcConfigTip();
return (-1); return (-1);
} }
@ -516,9 +532,35 @@ IpcMemoryCreate(IpcMemoryKey memKey, uint32 size, int permission)
if (shmid < 0) if (shmid < 0)
{ {
fprintf(stderr, "IpcMemoryCreate: shmget(%d, %d, 0%o) failed: %s\n", fprintf(stderr, "IpcMemoryCreate: shmget(key=%d, size=%d, 0%o) failed: %s\n",
memKey, size, (unsigned)(IPC_CREAT|permission), strerror(errno)); (int)memKey, size, (unsigned)(IPC_CREAT|permission),
IpcConfigTip(); strerror(errno));
if (errno == EINVAL)
fprintf(stderr,
"\nThis error can be caused by one of three things:\n\n"
"1. The maximum size for shared memory segments on your system was\n"
" exceeded. You need to raise the SHMMAX parameter in your kernel\n"
" to be at least %d bytes.\n\n"
"2. The requested shared memory segment was too small for your system.\n"
" You need to lower the SHMMIN parameter in your kernel.\n\n"
"3. The requested shared memory segment already exists but is of the\n"
" wrong size. This is most likely the case if an old version of\n"
" PostgreSQL crashed and didn't clean up. The `ipcclean' utility\n"
" can be used to remedy this.\n\n"
"The PostgreSQL Administrator's Guide contains more information about\n"
"shared memory configuration.\n\n",
size);
else if (errno == ENOSPC)
fprintf(stderr,
"\nThis error does *not* mean that you have run out of disk space.\n\n"
"It occurs either if all available shared memory ids have been taken,\n"
"in which case you need to raise the SHMMNI parameter in your kernel,\n"
"or because the system's overall limit for shared memory has been\n"
"reached. The PostgreSQL Administrator's Guide contains more\n"
"information about shared memory configuration.\n\n");
return IpcMemCreationFailed; return IpcMemCreationFailed;
} }
@ -541,7 +583,7 @@ IpcMemoryIdGet(IpcMemoryKey memKey, uint32 size)
if (shmid < 0) if (shmid < 0)
{ {
fprintf(stderr, "IpcMemoryIdGet: shmget(%d, %d, 0) failed: %s\n", fprintf(stderr, "IpcMemoryIdGet: shmget(key=%d, size=%d, 0) failed: %s\n",
memKey, size, strerror(errno)); memKey, size, strerror(errno));
return IpcMemIdGetFailed; return IpcMemIdGetFailed;
} }
@ -558,7 +600,7 @@ static void
IpcMemoryDetach(int status, char *shmaddr) IpcMemoryDetach(int status, char *shmaddr)
{ {
if (shmdt(shmaddr) < 0) if (shmdt(shmaddr) < 0)
elog(NOTICE, "IpcMemoryDetach: shmdt(0x%p): %m", shmaddr); elog(NOTICE, "IpcMemoryDetach: shmdt(0x%p) failed: %m", shmaddr);
} }
/****************************************************************************/ /****************************************************************************/
@ -694,13 +736,3 @@ LockIsFree(int lockid)
#endif #endif
#endif /* HAS_TEST_AND_SET */ #endif /* HAS_TEST_AND_SET */
static void
IpcConfigTip(void)
{
fprintf(stderr, "This type of error is usually caused by an improper\n");
fprintf(stderr, "shared memory or System V IPC semaphore configuration.\n");
fprintf(stderr, "For more information, see the FAQ and platform-specific\n");
fprintf(stderr, "FAQ's in the source directory pgsql/doc or on our\n");
fprintf(stderr, "web site at http://www.postgresql.org.\n");
}