Update shared memory configuration information for Linux

In particular, the assertion that shmall is sufficiently sized by default
is slowly becoming untrue.

diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 97e2c9807e78c8dd947879a50d766e657cfd9bca..1eaab5110508fcdb4218e7bcb6284a56e79f547e 100644 (file)
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -1,4 +1,4 @@
-
+
 
 
  Server Setup and Operation
@@ -522,9 +522,10 @@ psql: could not connect to server: No such file or directory
     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 a BSD heritage. (On Windows,
+    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.)
@@ -535,6 +536,7 @@ psql: could not connect to server: No such file or directory
     Illegal system call error upon server start. In
     that case there is no alternative but to reconfigure your
     kernel.  PostgreSQL won't work without them.
+    This situation is rare, however, among modern operating systems.
    
 
    
@@ -546,8 +548,6 @@ psql: could not connect to server: No such file or directory
     parameters are named consistently across different systems; 
     linkend="sysvipc-parameters"> 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.
    
 
 
@@ -643,15 +643,15 @@ psql: could not connect to server: No such file or directory
     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 tens to hundreds of megabytes.
+    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.  (Caution: SHMALL
-    is measured in pages rather than bytes on many systems.)
+    are using shared memory segments.  Note that SHMALL
+    is measured in pages rather than bytes on many systems.
    
 
    
@@ -898,30 +898,41 @@ options        SEMMAP=256
       
        
         The default maximum segment size is 32 MB, which is only adequate
-        for small PostgreSQL installations.
-        However, the remaining
-        defaults are quite generously sized, and usually do not require
-        changes. The maximum shared memory segment size can be changed via the 
-        sysctl interface.  For example, to allow 128 MB, 
-        and explicitly set the maximum total shared memory size to 2097152 
-        pages (the default):
+        for very small PostgreSQL
+        installations.  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.
+       
+
+       
+        The shared memory size settings can be changed via the
+        sysctl interface.  For example, to allow 16 GB:
 
-$ sysctl -w kernel.shmmax=134217728
-$ sysctl -w kernel.shmall=2097152
+$ sysctl -w kernel.shmmax=17179869184
+$ sysctl -w kernel.shmall=4194304
 
-        In addition these settings can be preserved  between reboots in
-        the file /etc/sysctl.conf.
+        In addition these settings can be preserved between reboots in
+        the file /etc/sysctl.conf.  Doing that is
+        highly recommended.
        
 
        
-        Older distributions might not have the sysctl program,
+        Ancient distributions might not have the sysctl program,
         but equivalent changes can be made by manipulating the 
         /proc file system:
 
-$ echo 134217728 >/proc/sys/kernel/shmmax
-$ echo 2097152 >/proc/sys/kernel/shmall
+$ echo 17179869184 >/proc/sys/kernel/shmmax
+$ echo 4194304 >/proc/sys/kernel/shmall
 
        
+
+       
+        The remaining defaults are quite generously sized, and usually
+        do not require changes.
+