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Re: Antw: Re: contextCSN values and MMR


On Mon, 12 Aug 2013, Michael StrÃder wrote:
Christian Kratzer wrote:
On Mon, 12 Aug 2013, Ulrich Windl wrote:
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.

Not sure though.

do you "query" by slapcat or by an LDAP search? For the former it's documented
that contextCSN is updated lazily. For the latter I'm not sure.

I have had the same use case Michael is getting at in the back of me
head for some time.  I would also like to verify replication status by
checking the contextCSN on all servers via an ldapsearch from a
monitoring script.

I would expect an ldapsearch of the contextCSN to deliver a current
and valid value that should be identical over all servers.

It seems this is not the case.  I will run a couple of tests to verify
this myself in my testbed of 2 mmr masters and 2 slaves.

Even worse my results with 3 MMR providers and 2 read-only consumer replicas
are sometimes not very pleasant regarding data consistency. At the moment this
test servers are running as VMs on ESX server. I will repeat my tests with
real hardware to make sure there's nothing wrong because of the virtual

I have a mixed hardware / virtualisation based environment available.  Will check the contextCSN over there and let you know.

Using delta-sync MMR does not make sense in my case because entries will be
completely added, modified or delete. (I have no influence on the client app
writing there.)

same here.  I also like the added bonus of giving the customer a stable and easy recovery roadmap of:

- stop slapd
- rm -f /var/lib/ldap/*
- start slapd

The customer has a relatively small dataset so replication is a matter seconds or at least under a couple of minutes.


Christian Kratzer                      CK Software GmbH
Email:   ck@cksoft.de                  Wildberger Weg 24/2
Phone:   +49 7032 893 997 - 0          D-71126 Gaeufelden
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Web:     http://www.cksoft.de/         Geschaeftsfuehrer: Christian Kratzer