Document how to prevent PostgreSQL itself from exhausting memory.

The existing documentation in Linux Memory Overcommit seemed to
assume that PostgreSQL itself could never be the problem, or at
least it didn't tell you what to do about it.

Per discussion with Craig Ringer and Kevin Grittner.

1 files changed, 16 insertions, 2 deletions

diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 36982b748a4..a47c998524d 100644
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -1203,8 +1203,9 @@ default:\
     optimal for <productname>PostgreSQL</productname>. Because of the
     way that the kernel implements memory overcommit, the kernel might
     terminate the <productname>PostgreSQL</productname> postmaster (the
-    master server process) if the memory demands of
-    another process cause the system to run out of virtual memory.
+    master server process) if the memory demands of either
+    <productname>PostgreSQL</productname> or another process cause the
+    system to run out of virtual memory.
    </para>
 
    <para>
@@ -1232,6 +1233,19 @@ Out of Memory: Killed process 12345 (postgres).
    </para>
 
    <para>
+    If <productname>PostgreSQL</productname> itself is the cause of the
+    system running out of memory, you can avoid the problem by changing
+    your configuration.  In some cases, it may help to lower memory-related
+    configuration parameters, particularly
+    <link linkend="guc-shared-buffers"><varname>shared_buffers</></link>
+    and <link linkend="guc-work-mem"><varname>work_mem</></link>.  In
+    other cases, the problem may be caused by allowing too many connections
+    to the database server itself.  In many cases, it may be better to reduce
+    <link linkend="guc-max-connections"><varname>max_connections</></link>
+    and instead make use of external connection-pooling software.
+   </para>
+
+   <para>
     On Linux 2.6 and later, it is possible to modify the
     kernel's behavior so that it will not <quote>overcommit</> memory.
     Although this setting will not prevent the <ulink