Re: contextCSN values and MMR

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

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).
>> 
>> Ciao, Michael.
> 
> I always set the syncprov checkpoint on all servers, replicas or masters. 
> 
> --Quanah

Correction. I load slapo-syncprov on all replicated db backends. I don't set the checkpoint.