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| -rw-r--r-- | doc/src/sgml/runtime.sgml | 59 |
1 files changed, 53 insertions, 6 deletions
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml index d74cf993d98..eabc67c646f 100644 --- a/doc/src/sgml/runtime.sgml +++ b/doc/src/sgml/runtime.sgml @@ -1,5 +1,5 @@ <!-- -$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.201 2003/08/31 17:32:19 petere Exp $ +$Header: /cvsroot/pgsql/doc/src/sgml/runtime.sgml,v 1.202 2003/09/05 02:54:09 momjian Exp $ --> <Chapter Id="runtime"> @@ -3081,14 +3081,61 @@ kernel.shmmax = 134217728 </para> <para> - Linux has poor default memory overcommit behavior. Rather than - failing if it can not reserve enough memory, it returns success, - but later fails when the memory can't be mapped and terminates - the application with <literal>kill -9</>. To prevent unpredictable - process termination, use: + Linux kernel version 2.4.* has poor default memory overcommit + behavior, which can result in the postmaster being killed by the + kernel due to memory demands by another process if the system + runs out of memory. + </para> + + <para> + The symptom of this occuring is a kernel message looking like + this (consult your system documentation and configuration on + where to look for such a message): +<programlisting> + Out of Memory: Killed process 12345 (postmaster). +</programlisting> + </para> + + <para> + To avoid this situation, run <productname>PostgreSQL</productname> + on a machine where you + can be sure that other processes will not run the machine out + of memory. If your kernel supports strict and/or paranoid modes + of overcommit handling, you can also relieve this problem by + altering the system's default behaviour. This can be determined + by examining the function <function>vm_enough_memory</> + in the file <filename>mm/mmap.c</>in the kernel source. + If this file reveals that strict and/or paranoid modes are + supported by your kernel, turn one of these modes on by using +<programlisting> +sysctl -w vm.overcommit_memory=2 +</programlisting> + for strict mode or <programlisting> sysctl -w vm.overcommit_memory=3 </programlisting> + for paranoid mode, or placing an equivalent entry in + <filename>/etc/sysctl.conf</>. + </para> + + <note> + <para> + Warning: using these settings in a kernel which does not support + these modes will almost certainly increase the danger of the + kernel killing the postmaster, rather than reducing it. + If in any doubt, consult a kernel expert or your kernel vendor. + </para> + </note> + + <para> + These modes are expected to be supported in all 2.6 and later + kernels. Some vendor 2.4 kernels may also support these modes. + However, it is known that some vendor documents suggest that + they support them while examination of the kernel source reveals + that they do not. + </para> + + <para> Note, you will need enough swap space to cover all your memory needs. </para> </listitem> |