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From Doron Cohen <>
Subject Re: Proposal about Version API "relaxation"
Date Mon, 19 Apr 2010 08:28:01 GMT
Late joining... could we agree on an "intention" to provide an index
migration tool when/if format back comp. has to be broken? It is not clear
to me that this was agreed... So here is a suggestion for a revised index
format backwards compatibility policy:

Starting release 4.0, Lucene has a limited file formats back-compatibility
between major versions, falling into one of the three possible levels:
(Level 1) When possible, Version X is would be able to read indexes
generated by any X-1 version after and including version X-1.0. (Level 2) If
version X cannot read indexes of version X-1, the release of version X would
be accompanied by a tool for migrating indexes from X-1 to X, unless (Level
3) the nature of the specific change does not allow for the development of
such a migration tool. For the exact level of file back compatibility of a
release see the specific release notes.

Not sure if the "unless" part (no. 3) would ever materialize, but I think it
provides a required freedom.


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