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From DM Smith <>
Subject Re: Back Compatibility
Date Wed, 23 Jan 2008 23:24:26 GMT
Top posting because this is a response to the thread as a whole.

It appears that this thread has identified some different reasons for  
"needing" to break compatibility:
1) A current behavior is now deemed bad or wrong. Examples: the silent  
truncation of large documents or an analyzer that works incorrectly.
2) Performance tuning such as seen in Token, allowing reuse.
3) Support of a new language feature, e.g. generics, that make the  
code "better".
4) A new feature requires a change to the existing API.

Perhaps there were others? Maybe specifics are in Jira.

It seems to me that the Lucene developers have done an excellent job  
at figuring out how to maintain compatibility. This is a testament to  
how well grounded the design of the API actually is, from early on and  
even now. And changes seem to be well thought out, well designed and  
carefully implemented.

I think that when it really gets down to it, the Lucene API will stay  
very stable because of this.

On a side note, the cLucene project seems to be languishing (still  
trying to get to 2.0) and any stability of the API is a good thing for  
it. And perhaps for the other "ports" as well.

Again many thanks for all your hard work,
	DM Smith, a thankful "parasite" :)

On Jan 23, 2008, at 5:16 PM, Michael McCandless wrote:

> chris Hostetter wrote:
>> : I do like the idea of a static/system property to match legacy
>> : behavior.  For example, the bugs around how StandardTokenizer
>> : mislabels tokens (eg LUCENE-1100), this would be the perfect  
>> solution.
>> : Clearly those are silly bugs that should be fixed, quickly, with  
>> this
>> : back-compatible mode to keep the bug in place.
>> :
>> : We might want to, instead, have ctors for many classes take a  
>> required
>> : arg which states the version of Lucene you are using?  So if you  
>> are
>> : writing a new app you would pass in the current version.  Then, on
>> : dropping in a future Lucene JAR, we could use that arg to enforce  
>> the
>> : right backwards compatibility.  This would save users from having  
>> to
>> : realize they are hitting one of these situations and then know to  
>> go
>> : set the right static/property to retain the buggy behavior.
>> I'm not sure that this would be better though ... when i write my  
>> code, i
>> pass "2.3" to all these constructors (or factory methods) and then  
>> later i
>> want to upgrade to 2.3 to get all the new performance goodness ... i
>> shouldn't have to change all those constructor calls to get all the  
>> 2.4
>> goodness, i should be able to leave my code as is -- but if i do  
>> that,
>> then i might not get all the 2.4 goodness, (like improved
>> tokenization, or more precise segment merging) because some of that
>> goodness violates previous assumptions that some code might have  
>> had ...
>> my code doesn't have those assumptions, i know nothing about them,  
>> i'll
>> take whatever behavior the Lucene Developers recommend (unless i see
>> evidence that it breaks something, in which case i'll happily set a
>> system property or something that the release notes say will force  
>> the
>> old behavior.
>> The basic principle being: by default, give users the behavior that  
>> is
>> generally viewed as "correct" -- but give them the option to force
>> "uncorrect" legacy behavior.
> OK, I agree: the vast majority of users upgrading would in fact want  
> all of the changes in the new release.  And then the rare user who  
> is affected by that bug fix to StandardTokenizer would have to set  
> the compatibility mode.  So it makes sense for you to get all  
> changes on upgrading (and NOT specify the legacy version in all  
> ctors).
>> : Also, backporting is extremely costly over time.  I'd much rather  
>> keep
>> : compatibility for longer on our forward releases, than spend our
>> : scarce resources moving changes back.
>> +1
>> : So to summarize ... I think we should have (keep) a high  
>> tolerance for
>> : cruft to maintain API compatibility.  I think our current approach
>> : (try hard to keep compatibility during "minor" releases, then
>> : deprecate, then remove APIs on a major release; do major releases  
>> only
>> : when truly required) is a good one.
>> i'm with you for the most part, it's just the defintion of "when  
>> truly
>> required" that tends to hang people up ... there's a chicken vs egg
>> problem of deciding wether the code should drive what the next  
>> release
>> number is: "i've added a bitch'n feature but it requires adding a  
>> method
>> to an interface, therefor the next release must be called 4.0" ...  
>> vs the
>> mindset that "we just had a 3.0 release, it's too soon for another  
>> major
>> release, the next release should be called 3.1, so we need to hold  
>> off on
>> commiting non backwards compatible changes for a while."
>> I'm in the first camp: version numbers should be descriptive,  
>> information
>> carrying, labels for releases -- but the version number of a release
>> should be dicated by the code contained in that release.  (if that  
>> means
>> the next version after 3.0.0 is 4.0.0, then so be it.)
> Well, I am weary of doing major releases too often.  Though I do  
> agree that the version number should be a "fastmatch" for reading  
> through CHANGES.txt.
> Say we do this, and zoom forward 2 years when we're up to 6.0, then  
> poor users stuck on 1.9 will dread upgrading, but probably shouldn't.
> One of the amazing things about Lucene, to me, is how many really  
> major changes we have been able to make while not in fact breaking  
> backwards compatibility (too much).  Being very careful not to make  
> things public, intentionally not committing to things like exactly  
> when does a flush or commit or merge actually happen, marking new  
> APIs as experimental and freely subject to change, using abstract  
> classes not interfaces, are all wonderful tools that Lucene employs  
> (and should continue to do so), to enable sizable changes in the  
> future while keeping backwards compatibility.
> Allowing for future backwards compatibility is one of the most  
> important things we all do when we make changes to Lucene!
> Mike
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