ITEM: FP1959L

Use CAUTION with EXTSHM

Use of Extended Shared Memory (environment variable EXTSHM=ON)
should NOT be configured globally in /etc/environment, and
caution should be used setting it in a profile.

Processes that use shared memory segments in a conventional
manner will fail if they run with in an environment with
EXTSHM=ON.

Some examples of applications that can fail include:

1.) Oracle when using async I/O (aio) has failed with the
following error in the Oracle Alert Log:
error=2893 txt: IBM AIX RISC System/6000 Error: 14: Bad address

2.)Spectra Logic's Alexandria backup software used in conjunction
with Oracle can hang the system or cause a system dump.  If
crash occurs during a hot backup connected to an Oracle
database, significant database recovery can be required.

3.)IBM SP development has also issued a statement that EXTSHM
is not and will not be supported by SP switch support code
(ssp.css.2.2.0.0 or any future release).

4.)The IBM StorX SSA mapping tool seems to hang and never
complete the maps.

You probably can run a mixed set of processes, some using
extended shared memory, and some using conventional shared
memory segments.  But those using extended should have 
EXTSHM set in the shell environment for that process only, 
perhaps by setting EXTSHM=ON in a script that then launches
 the process that uses it.




Support Line: Use CAUTION with EXTSHM ITEM: FP1959L

Dated: May 1998 Category: N/A

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