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From Mark Miller <>
Subject Re: Proposal for changing the backwards-compatibility policy
Date Tue, 16 Jun 2009 16:56:51 GMT
I'm inclined to agree to a large extent. If we want to remove 
deprecations more often, why not release major versions more often?

The main ramification I see being that the index back compat period 
could be significantly shortened time wise with the current policy.

DM Smith wrote:
> Michael Busch wrote:
>> Probably everyone is thinking right now "Oh no! Not again!". I admit I
>> didn't fully read the incredibly long recent thread about
>> backwards-compatibility, so maybe what I'm about to propose has been
>> proposed already. In that case my apologies in advance.
> Perhaps you should go back and see why the thread died. The points I 
> made earlier, at the end of the thread, are still pertinent. I'll 
> highlight some of that again.
>> Rather than discussing our current backwards-compatibility policy
>> again, I'd like to make here a concrete proposal for changing the policy
>> after Lucene 3.0 is released.
>> I'll call X.Y -> X+1.0 a 'major release', X.Y -> X.Y+1 a
>> 'minor release' and X.Y.Z -> X.Y.Z+1 a 'bugfix release'. (we can later
>> use different names; just for convenience here...)
>> 1. The file format backwards-compatiblity policy will remain unchanged;
>>    i.e. Lucene X.Y supports reading all indexes written with Lucene
>>    X-1.Y. That means Lucene 4.0 will not have to be able to read 2.x
>>    indexes.
> I'll reiterate what this means to me. It is more than just file format 
> stability. An index must still be useful. An index is invalidated if 
> the analyzers, filters and/or token streams produce a different 
> result. If these change, the index is not really readable.
>> 2. Deprecated public and protected APIs can be removed if they have
>>    been released in at least one major or minor release. E.g. an 3.1
>>    API can be released as deprecated in 3.2 and removed in 3.3 or 4.0
>>    (if 4.0 comes after 3.2).
> To support #2, in view of #1, we need robust test cases that focus on 
> input and output of the invariants of analyzers, filters and token 
> streams. We may already have this.
> Regarding #1 and #2, I think that bug fixes should not be held back 
> when it changes these outputs.
> I'll reiterate here too. This will cause Linux distributions, such as 
> Debian, to number Lucene differently. This will cause confusion.
> The Debian policy is to bump the major revision number every time 
> there is an incompatible API change.
> This really is not necessary. We already have a sufficient mechanism 
> to do #2: just do a major release. But it requires frequent releases.
>> 3. No public or protected APIs are changed in a bugfix release; except
>>    if a severe bug can't be changed otherwise.
> Just as important as the signatures, the input/output relationships 
> should not change, except to fix an undebatable bug.
>> 4. Each release will have release notes with a new section
>>    "Incompatible changes", which lists, as the names says, all 
>> changes that
>>    break backwards compatibility. The list should also have information
>>    about how to convert to the new API. I think the eclipse releases
>>    have such a release notes section.
>> The big change here apparently is 2. Consider the current situation:
>> We can release e.g. the new TokenStream API with 2.9; then we can
>> remove it a month later in 3.0, while still complying with our current
>> backwards-compatibility policy. A transition period of one month is
>> very short for such an important API. On the other hand, a transition
>> period of presumably >2 years, until 4.0 is released, seems very long
>> to stick with a deprecated API that clutters the APIs and docs. With
>> the proposed change, we couldn't do that. Given our current release
>> schedule, the transition period would at least be 6-9 months, which
>> seems a very reasonable timeframe.
>> We should also not consider 2. as a must. I.e. we don't *have* to
>> deprecate after one major or minor release already. We could for a
>> very popular API like the TokenStream API send a mail to java-user,
>> asking if people need more transition time and be flexible.
>> I think this policy is much more dynamic and flexible, but should
>> still give our users enough confidence. It also removes the need to
>> do things just for the sake of the current policy rather than because
>> they make the most sense, like our somewhat goofy X.9 releases. :)
>> Just to make myself clear: I think we should definitely stick with our
>> 2.9 and 3.0 plans and change the policy afterwards.
>> My +1 to all 4 points above.
>> -Michael
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- Mark

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