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https://issues.apache.org/jira/browse/LUCENE-3490?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13140810#comment-13140810
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Uwe Schindler commented on LUCENE-3490:
---------------------------------------
Just some comments:
The current impl is identical to how nio.Charset and nio.spi.CharsetProvider
works in JDK's NIO classes. This differs from TIKA, where no "*Provider" class
is used and all Parsers are listed in META-INF.
For nio.Charsets we generally have lots of different charset names and many of
them can be implemented by same classes with different parameters (e.g. there
is a single class for all ISO8859 charsets that just gets the table name as
ctor param).
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, we can remove the whole CodecProvider
interface and its implementations and instead use ServiceLoader<Codec> and
ServiceLoader<PostigsFormat> and list all codec classes in META-INF separately
(and not only the provider class). In that case the CodecLoader static helper
class would initialize the map name->Codec on init and will do lookup and list
of all codec names using that map. This would simplyfy the implementation, but
would remove the possibility to e.g. encode parameters into codec names (e.g.,
"pulsingLucene40" -> new PulsingPostingsFormat(new Lucene40PostingsFormat())
versus "pulsingPFOR" -> new PulsingPostingsFormat(new
PFORDeltaPostingsFormat()).
Any suggestions? If we want to simplify and remove CodecProvider, I can recode
this with minimal effort. In that case, the Chicken-And-Egg problem in
Lucene40Codec using PostingsFormat.forName() would also be solved [its the same
problem like the Java7-ICU-bug] :-)
> 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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