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https://issues.apache.org/jira/browse/SOLR-2338?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12992735#comment-12992735
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Robert Muir commented on SOLR-2338:
-----------------------------------
{quote}
...but even if we don't do that, i suppose it's also conceivable that someone
might have their own Similarity implementation that is expensive to instantiate
(ie: maintains some big in memory data structures?) and might want to be able
to declare one instance and then refer to it by name in many different
fieldType declarations.
{quote}
I don't think this is really a use case we need to support: the purpose of
Similarity today is to do term weighting, not to be a huge data-structure
holder.
While I know Mike's original patch went this way with LUCENE-2392 (e.g. norms),
I'm not sure i like it being in Similarity in the future either.
Otherwise concepts like lazy-loading norms and all this other stuff get pushed
onto the sim, which is an awkward place (imagine if you have many fields).
So, I think we shouldn't really design for abuses of the API. If there are
other use cases for "named similarity" that have to do with term weighting, I'm
interested.
> improved per-field similarity integration into schema.xml
> ---------------------------------------------------------
>
> Key: SOLR-2338
> URL: https://issues.apache.org/jira/browse/SOLR-2338
> Project: Solr
> Issue Type: Improvement
> Components: Schema and Analysis
> Affects Versions: 4.0
> Reporter: Robert Muir
>
> Currently since LUCENE-2236, we can enable Similarity per-field, but in
> schema.xml there is only a 'global' factory
> for the SimilarityProvider.
> In my opinion this is too low-level because to customize Similarity on a
> per-field basis, you have to set your own
> CustomSimilarityProvider with <similarity class=.../> and manage the
> per-field mapping yourself in java code.
> Instead I think it would be better if you just specify the Similarity in the
> FieldType, like after <analyzer>.
> As far as the example, one idea from LUCENE-1360 was to make a "short_text"
> or "metadata_text" used by the
> various metadata fields in the example that has better norm quantization for
> its shortness...
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