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https://issues.apache.org/jira/browse/LUCENE-5940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14130307#comment-14130307
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Tim Smith commented on LUCENE-5940:
-----------------------------------
i would not consider old indexes not containing support for new features an
issue.
if you want to use new options/features/structures, you need to reindex, no
problem here.
you don't have to convince me that supporting back compat sucks. i agree, but
lucene is used by a lot of people for a lot of disparate use cases. removing
support for back compat will drive people away since it removes seamless
upgrade paths.
think what would have happened if microsoft release 64-bit windows with no
support for running old 32-bit programs.
people still want to run old dos programs on windows (go figure, but they
want/need it)
it hurts adoption of new versions if you don't provide the back compat. this
just leaves a bunch of people running ancient versions of lucene because they
don't have any good upgrade path other than complete reindexing.
if there is a bug in "feature x", a possible solution is to just remove
"feature x", but this is gonna piss off everyone who relies on it, regardless
of how much you may personally hate "feature x"
the main thing i see as a challenge that you mention here is that you want (or
new features may require) refactoring the codec api.
this is an engineering challenge and would just require some thought out design
to decide what "final api refactors" should be needed to support flexibility,
addition of new features, and growth without requiring mucking with old codecs
in the future.
right now, the IndexWriter and codecs are pretty muddled together in some
cases. cleaning up these interfaces and making the codecs self contained should
be a goal for any refactors to allow future innovation/addition of features.
as a lucene user, if back compat is yanked and not provided in 5.0 for all 4.x
indexes, i will be extremely resistant to upgrade. I would be more inclined to
fork the latest 4.x and ditch 5.0. 5.0 would have to offer something REALLY
compelling to get me to adopt it.
> change index backwards compatibility policy.
> --------------------------------------------
>
> Key: LUCENE-5940
> URL: https://issues.apache.org/jira/browse/LUCENE-5940
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Robert Muir
>
> Currently, our index backwards compatibility is unmanageable. The length of
> time in which we must support old indexes is simply too long.
> The index back compat works like this: everyone wants it, but there are
> frequently bugs, and when push comes to shove, its not a very sexy thing to
> work on/fix, so its hard to get any help.
> Currently our back compat "promise" is just a broken promise, because we
> cannot actually guarantee it for these reasons.
> I propose we scale back the length of time for which we must support old
> indexes.
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