Re: understanding replication

On Mon, 1 Mar 2010, Alan Batie wrote:

> I'm a little puzzled by the openldap replication docs; in particular
> rid, entryuuid, entrycsn, contextcsn fields that I see referenced a lot.
[...]
> Basically, I'd like to understand the replication process at a slightly
> higher level than http://www.openldap.org/doc/admin24/syncrepl.html
> describes not quite completely enough...

In addition to the Admin Guide, I suggest reading RFC4533 and the other 
material in the doc/ directory of the distribution. Also, even if you're 
not particularly adept at C, you may wish to read the comments in 
syncprov.c source file. The terms you're asking about are the names that 
OpenLDAP uses in its implementation; hopefully with the RFC in hand it 
will become clear how the concepts map to the names, and you can always 
ask if anything is still unclear.

> I'm guessing the rid is a random chosen id number for the secondary
> server (consumer?) that is used to compare the master db (entryuuid?)
> for context? information that indicates sync state?

rid is chosen by administrator (i.e. manually configured). I honestly 
forget what it's used for nowadays...I vaguely remember "nothing" and/or 
"it's only important for multimaster." I'm certain this is in the archives 
of openldap-software and/or openldap-devel, but I'll leave the search to 
you.

> The specific task at hand is trying to understand what I'm seeing in the
> logs, having setup a master, loaded the db, configured replication,
> setup a fresh secondary mirror and turned on replication there.  I let
> it run over the weekend, and see debug logs of what I assume is polling
> on the secondary, but 'slapcat | grep -c "dn:"' returns (and has been
> for a while) a suspiciously round number of "500" (there are around
> 38,000 records in the master), though I don't see any such limit
> anywhere in the configs.

My take on this would be that, if you turned up debugging and/or created a 
packet capture, you will find LDAP_SIZELIMIT_EXCEEDED returned by the 
provider in response to the consumer search request. As for not seeing the 
limit, please read slapd.conf(5) man page thoroughly.

> master config:
>
> overlay syncprov
> syncprov-checkpoint 100 10
> syncprov-sessionlog 100

That take above would be more precise if you gave the unabridged provider 
config...