Hoss Man created LUCENE-5125:
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Summary: Codec classes/packages that do not provide file format
back compat need to be more explicit about this in javadocs
Key: LUCENE-5125
URL: https://issues.apache.org/jira/browse/LUCENE-5125
Project: Lucene - Core
Issue Type: Improvement
Reporter: Hoss Man
rmuir noted in LUCENE-5121...
bq. Currently (as documented), we don't provide index back compat for
experimental codecs in lucene-codecs.jar.
...but except for a solr wiki page and solrconfig.xml comment, it's extremely
non-obvious that any of these codec classes don't provide index backcompat.
* the codec module overview.html page describes the module as "Collection of
useful codec, postings format and terms dictionary implementations" -- with no
indication that by using these "useful" implementations, the user gives up
index backcompat.
* the package.html files in the individual packages of the codec module
(appending, blockterms, bbloom, diskdv, etc...) also say nothing about index
backcompat
* the individual classes in these codecs are mostly labeled with
{{@lucene.experimental}} but in the resulting javadoc that merely says that
"WARNING: This _API_ is experimental and might change in incompatible ways in
the next release". Lots of classes in Lucene have this warning on them about
their API (including the abstract codec apis themselves in lucene-core:
DocValuesFormat, PostingsFormat, etc...) and that annotation (as far back as i
can remember) has always only refered to the java API of the labeled class --
never to whether using that class ment you were giving up on index format back
compat.
Given how much effort and work is put into ensuring good index backcompat for
default codec, we should be extremely explicit when/if alternative codecs do
not support backcompat, so we don't frustrate/confuse users and leave them with
the impression that they can never count on index backcompat just because they
may not realize they were using an "unsupported" format option because of a
blog post they read or advice they got on the mailing list about how to make
something faster or use less ram.
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