Restructure codec hierarchy
---------------------------
Key: LUCENE-3490
URL: https://issues.apache.org/jira/browse/LUCENE-3490
Project: Lucene - Java
Issue Type: Improvement
Reporter: Robert Muir
Fix For: 4.0
Spinoff of LUCENE-2621. (Hoping we can do some of the renaming etc here in a
rote way to make progress).
Currently Codec.java only represents a portion of the index, but there are
other parts of the index
(stored fields, term vectors, fieldinfos, ...) that we want under codec
control. There is also some
inconsistency about what a Codec is currently, for example Memory and Pulsing
are really just
PostingsFormats, you might just apply them to a specific field. On the other
hand, PreFlex actually
is a Codec: it represents the Lucene 3.x index format (just not all parts yet).
I imagine we would
like SimpleText to be the same way.
So, I propose restructuring the classes so that we have something like:
* CodecProvider <-- codec name to Class resolution only
* Codec <-- represents the index format (PostingsFormat + FieldsFormat + ...)
* PostingsFormat: this is what Codec controls today, and Codec will return one
of these for a field.
* FieldsFormat: Stored Fields + Term Vectors + FieldInfos?
I think for PreFlex, it doesnt make sense to expose its PostingsFormat as a
'public' class, because preflex
can never be per-field so there is no use in allowing you to configure PreFlex
for a specific field.
Similarly, I think we should do the same thing for SimpleText. Nobody needs
SimpleText for production, it should
just be a Codec where we try to make as much of the index as plain text and
simple as possible for debugging/learning/etc.
So we don't need to expose its PostingsFormat. On the other hand, I don't think
we need Pulsing or Memory codecs,
because its pretty silly to make your entire index use one of their
PostingsFormats. To parallel with analysis:
PostingsFormat is like Tokenizer and Codec is like Analyzer, and we don't need
Analyzers to "show off" every Tokenizer.
Later, once we abstract FieldInfos reading/writing out of o.a.l.index into
codec control, we can also then
move the baked in PerFieldCodecWrapper out (it would basically be
PerFieldPostingsFormat). Privately it would
write the ids to the file like it does today. all 3.x hairy backwards code
would move to PreflexCodec. SimpleTextCodec
would get a plain text fieldinfos impl, etc.
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