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From "Robert Muir (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-3490) Restructure codec hierarchy
Date Tue, 01 Nov 2011 02:24:32 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-3490?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13140858#comment-13140858
] 

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

{quote}
If we decide for Codecs, that the part that can read an index is always implemented by only
one class (PulsingPostingsFormat is currently the only problematic one) with a default ctor,
{quote}

+1

In my opinion (i added nocommit already), its fine for Pulsing(PostingsFormat wrapped) to
be abstract. But we should have Pulsing40 or something that is a concrete implementation.

All codecs/postings formats should be able to be instantiated with a no-arg ctor for reading.
If they took parameters for writing, they should also store these in the index so that the
index documents what its format is... this is really important. Currently we do this with
all parameters, we just need to fix pulsing. If someone wants to make PulsingHuperCodec we
allow them to do this, they just make a concrete one and they are done. I think we need only
provide Pulsing40 out of box and just leave the abstract wrapper API available for anyone
to use themselves.

Thanks for doing all this work Uwe... its a really good step forward... if you feel like doing
the simplification I am all for it :)

                
> 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
>
>         Attachments: LUCENE-3490_SPI.patch
>
>
> 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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