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Re: (ITS#8100) Empty accesslog causes issues with delta-syncrepl MMR configurations

quanah@symas.com wrote:
> --On Thursday, April 09, 2015 5:42 AM +0000 quanah@openldap.org wrote:
> 
>> Full_Name: Quanah Gibson-Mount
>> Version: 2.4.39
>> OS: Linux 2.6
>> URL: ftp://ftp.openldap.org/incoming/
>> Submission from: (NULL) (50.25.188.166)
>>
>>
>> When one has an MMR setup using delta-syncrepl, and the masters get into a
>> situation where one is out of sync, or adding a new MMR node to an
>> existing cluster, things will be broken until the new/reloaded node has a
>> write op that goes to the accesslog DB.  In an existing cluster, where a
>> node is being reloaded, it causes all nodes to go into an endless looping
>> fallback sync until that write occurs.
> 
> One possible fix for this, would be to refuse to delete the final entry in
> the accesslog during the purge phase.  That way, the accesslog would never
> be empty.  I'm not sure how difficult this would be to implement, code wise.

A patch which skips deleting the final entry, and creates an initial dummy log 
entry if needed, is available in 
https://github.com/quanah/openldap-scratch/tree/its8100 for testing.

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