Re: Troubleshooting synchronization

[Howard Chu <hyc@symas.com>]

Torsten Schlabach (Tascel eG) wrote:
> Hi Howard!
> 
>>> MirrorMode relies on an external frontend to direct all updates to a single
>>> provider. There is no difference within the OpenLDAP code between MirrorMode
>>> and MultiMaster; the difference is entirely external, based on your deployment.
> 
> So when you say: "We recommend not to use MMR", you're not saying don't
> use code section X of openldap but use code section Y, but you're
> basically saying: Do not send different updates to different providers
> at the same time, right?

Yes.

> In other words: If I would configure MMR between say 3 nodes but I would
> make sure that only one of them will receive updates at a time while on
> the other two there will only be read operations, then I have MirrorMode?
> 
> Is that right?

Yes.

>>> for new updates; in refreshAndPersist mode it will keep an LDAP session open
>>> and receive updates as they occur.
> 
> Could I query a provider to show me the current open sessions held by
> the consumers?

You can get a look at open sessions from cn=monitor but I don't think the
syncrepl sessions are highlighted in any particular way. What are you
expecting this to tell you?

> When is refreshOnly and when is refreshAndPersist recommended?

We don't make any particular recommendation. Some sites want "instantaneous"
replication; for them refreshAndPersist is the obvious choice. Other sites
only need coarse synchronization, or don't want to have long-lived LDAP
sessions open all the time. So they choose refreshOnly. On my G1 phone my
slapd is configured in refreshOnly syncing my home addressbook (with a 12 hour
refresh interval) because I just don't make changes often enough for it to matter.

> I was always confused in the documentation, as it says: sncrepl is
> entirely a client side technology and then it says you have the option
> to either pull or push updates. Now this becomes a bit clearer to me.
> Thanks for that.

-- 
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/