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Re: Configuring shared memory / memory mapped files

Hello Howard,

Thanks for the helpful information!
All about the  back-mdb sounds so good! Will the new back-mdb included
in the next release?
Is it recommended to use this backend in production environment?

Thanks for hard work on the great OpenLDAP!


2011/11/1 Howard Chu <hyc@symas.com>:
> Meike Stone wrote:
>> Hello,
>> time ago, we installed a Linux Guest with OpenLDAP (db size appox.
>> 650MByte / ) server in a ESXi environment.
>> Maybe because of a read/write ratio 100:1, the hard discs where heavy
>> used by writing bdb backends memory mapped files.
>> The CPU in that Linux system had iowait (top) between 80% and 100% and
>> the other VMs on the ESXi went slow down.
>> After changing to shared memory (shm_key), all problems with disc IO where
>> gone.
>> I read in the mailing list and on "OpenLDAP performance tuning" guide,
>> that it does not matter if using memory mapped files or shared memory
>> until the database is over 8GB. But why we had such problems?
>> Please note, the OpenLDAP was operating very fast with the memory
>> mapped files, because of using indexes and proper caching.
>> Now, I want install more than one OpenLDAP server on one Linux system
>> (now real Hardware).
>> Every OpenLDAP server will be bind on a separate IP and DNS host name.
>> So in this scenario it is hard to calculate the shared memory and
>> assign each LDAP server to the right shared memory region (key).
>> Therefore I want go back to memory mapped files. Are there any
>> recommendation for sizing the Linux system like:
>>  - type of file system (ext3, ext4, xfs, ..)
>>  - parameters of file system (syncing ->  commit=nrsec, data=*, ... )
>>  - swap using (swappiness, dirty_background_ratio)
>>  - ???
> Also, back-mdb (in git master) will behave much better in a VM deployment.
> (Actually, back-mdb behaves better than back-bdb/hdb in all environments.)
> --
>  -- Howard Chu
>  CTO, Symas Corp.           http://www.symas.com
>  Director, Highland Sun     http://highlandsun.com/hyc/
>  Chief Architect, OpenLDAP  http://www.openldap.org/project/