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From Michael McCandless <luc...@mikemccandless.com>
Subject Re: Lucene's default settings & back compatibility
Date Thu, 21 May 2009 21:55:57 GMT
On Thu, May 21, 2009 at 5:44 PM, Robert Muir <rcmuir@gmail.com> wrote:
> and what if your analyzer needs a third-party library (or two)?

In such cases the back-compat of your analyzer is your responsibility,
right?

> i mean this isn't unique to analyzers, if something changes/bug is fixed in
> the guts of some query/scorer that affects scoring in the slightest then
> thats a potential issue too, right?
>
> for a big index burying a result deep is effectively the same as the
> stopword example...

If it's a bug fix, or a change in order-of-operations causing slightly
different floating point truncations, we are free to make those fixes
(even under the current back-compat policy)?  Ie, nothing is changing
for those cases.

But, say we found some improvement to how Lucene does scoring, and by
and large it improves relevance so we want to do it.  New users should
see this benefit.  Back-compat users, I think, should be able to set
actsAsVersion to get back to the old scoring model.

So yeah I think I agree it's not just changes that affect what gets
indexed, but also changes that affect how scores are computed, where
we need a way to specify a back-compat version on upgrading.

I think we can't get away with only policy changes here... I think we
need actsAsVersion to preserve back-compat.

Mike

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