There is now code in Domino which, when enabled, will instruct Domino to
pre-allocate shared memory at startup, thus preventing the possibility of the
server "crashing" with an error of the type "Error attaching to shared memory"
or "Error on mapping memory" during extended Domino server operation. This is
due to the fact that at Domino startup, we will immediately allocate/map in our
maximum amount of useable shared memory and never again create any more shared
memory, thus preventing the possibility of a later process allocating shared
memory that other processes cannot map into their address space. The downside
of this is that we will always automatically use up this amount of virtual
memory for shared memory and thus will be capped on available local memory
based on the addressable memory available to Domino on the operating system.
For example, with this code enabled, on Windows we will pre-allocate 1.5 GB of
shared memory (default setting for Constrained Shared memory, changeable via
ConstrainedSHMSizeMB NOTES.INI setting) and with an addressable memory of 2 GB
(default value for Windows to match default setting of OS, changeable via
MEM_AddressableMemSizeMB NOTES.INI setting and OS configuration) that only
leaves 512mb for local memory. The upside is that running out of memory either
in shared or local will not crash the server (or should not), whereas the
inability to map shared memory always will.
This new code is off by default and must be enabled by setting
MEM_EnablePreAlloc=1 in NOTES.INI.
In order for this new code to work, we had to enable the sub-allocation of
shared memory when pre-allocation is turned on (can be manually enabled if
desired and do not wish to pre-allocate by setting MEM_EnableSubAlloc=1 in
NOTES.INI; Sub-allocation is only on by default on AIX). With sub-allocation,
we create shared memory as large "segments" and then sub-allocate our memory
pools out of them. For example, on Windows the size for a "segment" is ~200MB
(default setting for sub-allocate Shared Memory segment size, changeable via
MEM_SHMSubAllocSize (in bytes) NOTES.INI setting) and we will then create our
memory allocations out of it based on our shared dpool size of 4MB (default
setting on Windows, changeable via SHARED_DPOOLSIZE (in bytes) NOTES.INI
setting). This does limit the maximum single allocation size to the size of a
"segment" - in this case ~200MB - but internally Domino makes no memory
requests of this size, nor should any API program; an allocation request over
this size will fail.
There are also some changes/additions to our memory variables which are set
the NOTES.INI file:
1. As stated previously, the variable "MEM_EnableSubAlloc=1" will enable
sub-allocation of shared memory.
2. As stated previously, the variable "MEM_SHMSubAllocSize=VALUE" can be
to override our default setting for the size of a sub-allocated "segment" of
shared memory (where VALUE is in bytes, and the default varies by platform).
3. As stated previously, the variable "MEM_EnablePreAlloc=1" will enable
pre-allocation of shared memory and will also enable sub-allocation as well.
(Setting this variable enables ConstrainedSHM and MEM_AddressableMem as
4. The variable "ConstrainedSHM=1" will now enable the constraining of
memory only - it will not directly inhibit "addressable" memory as before but
will enable MEM_AddressableMem.
5. The variable "ConstrainedSHMSizeMB=VALUE" can still be used to override
default setting for constrained shared memory (where VALUE is in megabytes, and
the default varies by platform).
6. The variable "MEM_AddressableMem=1" will enable code to limit the amount
memory we see as "addressable". Without this set there is still a default limit
in place of 4GB and with the setting enabled more realistic values are used.
7. The variable "MEM_AddressableMemSizeMB=VALUE" can be used to override our
default setting for the amount of memory Domino will see as "addressable"
memory (where VALUE is in megabytes, and the default varies by platform).
8. There is now a variable on UNIX to enable using "mmap" for shared memory
"MEM_EnableMmap=1". This is on by default on Solaris only and is not presently
supported on any other platform (minimal testing has been done on Linux
9. There is now a variable to specify the location for where Domino will
"mmap" shared memory files - "MEM_Mmap_Location=FOO" where FOO is the absolute
path to the new location. This variable is only valid for platforms running
with "mmap" shared memory.
None, although you can specify this setting in the NOTES.INI Settings tab of
the Configuration Settings document in the Domino Directory.
MEM_EnableSubAlloc=0 / 1
Lotus Notes/Domino 7.0
Lotus Notes/Domino x.x.x