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From Andreas Sewe <andreas.s...@codetrails.com>
Subject Re: 5.x to 6.x migration: replacement for Lucene50Codec
Date Thu, 30 Mar 2017 09:41:34 GMT
Hi Uwe,

>>> I should have mentioned that I for compatibility reasons still need to
>>> be able to read/write indexes created with the old version, i.e., with
>>> the 5.0 codec.
> 
> The old codecs are read-only! As said before, you can only specify the codec for IndexWriter.
That means new segemnts to already existing indexes will automatically use the new codec.
Old segments already in your index will stay with the old codec, until they are merged away,
in which case they are implicitly upgraded.

Just to be clear: If lucene-backwards-codecs.jar 6.1 is on the classpath
(and gives me access to Lucene50Codec), can I specify the Lucene50Codec
in the IndexWriter's IndexWriterConfig and thus get Lucene 6.1 to write
an index compatible with Lucene 5.0?

> As the Lucene 5 codec is read only, it is impossible to create a new index (or modify
an existing index) in a way that it will still be readable with Lucene 5. As soon as you touch
an index with the new codec, it will be mixed codec versions and cannot be read with old version.
But Lucene 6 will happily handle the mixed codec index - it is designed for that use case
(default-codec indexes will behave the same way). 😊

That's a cool feature and may work well for my use case. The only thing
I worry about is how ServiceLoader-based Codec discovery will work in an
OSGi environment (specially, an Eclipse plug-in).

Best wishes,

Andreas

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