It is also extremely important that you backup and archive your index before opening it with Lucene 2.9, as it will make changes to the index that may not be readable by previous versions. Again, we strongly recommend a careful reading of the CHANGES.txt file included in every Lucene distribution, especially the sections on back-compatibility policy and on changes in runtime behavior. Careful study followed by proper planning and testing should prevent you from running into any surprises once the new Lucene 2.9-based application goes into production.
Upgrade to 2.9—Optional Actions Lucene 2.9 includes many new features that are not required for use of the new release. Nevertheless, 2.9 has numerous parts of the API marked as deprecated, since they are to be removed in the next release. To prepare for the next release and further improvements in this direction, it is strongly recommended that you replace any deprecated API during the upgrade process. Applications using any kind of numeric searches can improve their performance heavily by replacing custom solution with Lucene's Numeric Capabilities described earlier in this white paper. Last but not least, the new TokenStream API will replace the older API entirely in the next release. Custom TokenStream, TokenFilter, and Tokenizer implementations should be updated to the attribute-based API. Here, the source distribution contains basic test cases that can help you safely upgrade. Finally, to reiterate, you would do best to write new added test cases against their current Lucene version, and upgrade the test and your code once you have gained enough confidence in the stability of the upgrade.
What’s New in Lucene 2.9 A Lucid Imagination Technical White Paper • October 2009
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