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Re: (ITS#7472) syncrepl conflicting write resolution trouble
- To: openldap-its@OpenLDAP.org
- Subject: Re: (ITS#7472) syncrepl conflicting write resolution trouble
- From: firstname.lastname@example.org
- Date: Wed, 12 Dec 2012 05:00:40 GMT
- Auto-submitted: auto-generated (OpenLDAP-ITS)
> Full_Name: Emily Backes
> Version: 2.4.33+ITS#7427
> Submission from: (NULL) (126.96.36.199)
> We are seeing a condition under heavy conflicting-write load-- i.e. changes to
> the same DN from multiple nodes in a syncrepl MMR cluster at the same time--
> where the content of the entry is desynchronized between servers.
> There is a non-reproduced case with incomplete logs where servers traded entry
> versions, even with one CSN significantly (by one second) later than the other.
> I'll supply more info if that reappears.
> Additionally, we have a -d logged case of a conflicting write resulting in
> different changes applied on different servers while the same CSN gets applied
> to both, which seems truly bizarre.
> The expected case is that one server "wins" the conflict and its state is sent
> to all of the others, eventually.
Analyzing the logs shows this is an unresolvable conflict in plain
syncrepl/MMR. Please note that the Admin Guide already documents the fact that
consistency is not guaranteed in this mode. (Section 188.8.131.52.)
The solution, as documented, is to use mirrormode.
> All of these results are using back-hdb. More details soon, hopefully.
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/