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From "Robert Muir (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-3490) Restructure codec hierarchy
Date Sun, 30 Oct 2011 15:54:32 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-3490?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13139650#comment-13139650
] 

Robert Muir commented on LUCENE-3490:
-------------------------------------

Another thing, I would like to remove CodecProvider completely. 

I think Uwe has a good idea in LUCENE-2915.

The idea would be that we use this for index reading, when we read the 
codec name from the segments file, we use the ServiceLoader mechanism
to map that back to a Codec. Parameters should be no problem, when *reading*
all codecs should be able to use a no-arg ctor and any necessary parameters
should really be written into the index (otherwise the index does not document
how it should be read!)

For writing, I think IndexWriter would just optionally take Codec, what is to
be used for writing new segments.
                
> 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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