Re: contextCSN values and MMR

[Quanah Gibson-Mount <quanah@zimbra.com>]

On Aug 11, 2013, at 7:41 AM, Michael StrÃder <michael@stroeder.com> wrote:

> Quanah Gibson-Mount wrote:
>> On Aug 10, 2013, at 12:01 PM, Quanah Gibson-Mount <quanah@zimbra.com> wrote:
>>> On Aug 10, 2013, at 11:08 AM, Michael StrÃder <michael@stroeder.com> wrote:
>>>> Christian Kratzer wrote:
>>>>> On Sat, 10 Aug 2013, Michael StrÃder wrote:
>>>>>> Are contextCSN values on all replicas really in sync if changes were correctly
>>>>>> replicated?
>>>>>> 
>>>>>> I've implemented a monitoring check used with normal MMR setup (OpenLDAP
>>>>>> 2.4.35, own build on Debian Squeeze) which also checks the contextCSN values
>>>>>> on all replicas compared by server-id.
>>>>>> 
>>>>>> Sometimes we observe, even in isolated tests, that contextCSN values for a
>>>>>> certain server-id differ for quite a while (up to hours) even though the
>>>>>> changes coming from that server were definitely replicated to all other
>>>>>> replicas. After a while the contextCSN values get suddenly updated.
>>>>>> Unfortunately this does not always happen.
>>>>>> 
>>>>>> Any hint is highly appreciated.
>>>>> 
>>>>> I have always suspected that this is due to the specific setting of:
>>>>> 
>>>>>     syncprov-checkpoint <ops> <minutes>
>>>>>            After a write operation has succeeded, write the contextCSN to
>>>>> the underlying database  if  <ops>  write
>>>>>            operations  or more than <minutes> time have passed since the
>>>>> last checkpoint. Checkpointing is disabled
>>>>>            by default.
>>>> 
>>>> Thanks for following-up.
>>>> 
>>>> AFAICS the above directive specifys when to write the contextCSN to the DB on
>>>> disk similar to checkpoint directives for DB backends. So in case of a server
>>>> crashing you have a quite recent contextCSN with the server-id of this
>>>> particular server.
>>>> 
>>>> But since all replicas are up and running and I query the contextCSN values
>>>> via LDAP I presume this is not relevant for my problem. Well, one never knows
>>>> though...
>>>> 
>>>> => will try to play with this (I don't need a high write rate on those systems).
>>> 
>>> I always set the syncprov checkpoint on all servers, replicas or masters.
>> 
>> Correction. I load slapo-syncprov on all replicated db backends. I don't set the checkpoint.
> 
> As said this is a MMR setup
> => slapo-syncprov is loaded on all replicated DB backends
> 
> Anythings else why contextCSN is not updated?
> 
> Ciao, Michael.

Doesn't happen to me with delta-syncrepl based MMR. 

--Quanah