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https://issues.apache.org/jira/browse/SOLR-5354?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13811463#comment-13811463
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Robert Muir commented on SOLR-5354:
-----------------------------------
{quote}
Maybe solr needs its own SortField too then?
{quote}
OK I see it, I think solr should fix its own apis here? It could add
FieldType[] to SortSpec or something like that.
> Distributed sort is broken with CUSTOM FieldType
> ------------------------------------------------
>
> Key: SOLR-5354
> URL: https://issues.apache.org/jira/browse/SOLR-5354
> Project: Solr
> Issue Type: Bug
> Components: SearchComponents - other
> Affects Versions: 4.4, 4.5, 5.0
> Reporter: Jessica Cheng
> Assignee: Steve Rowe
> Labels: custom, query, sort
> Attachments: SOLR-5354.patch
>
>
> We added a custom field type to allow an indexed binary field type that
> supports search (exact match), prefix search, and sort as unsigned bytes
> lexicographical compare. For sort, BytesRef's UTF8SortedAsUnicodeComparator
> accomplishes what we want, and even though the name of the comparator
> mentions UTF8, it doesn't actually assume so and just does byte-level
> operation, so it's good. However, when we do this across different nodes, we
> run into an issue where in QueryComponent.doFieldSortValues:
> // Must do the same conversion when sorting by a
> // String field in Lucene, which returns the terms
> // data as BytesRef:
> if (val instanceof BytesRef) {
> UnicodeUtil.UTF8toUTF16((BytesRef)val, spare);
> field.setStringValue(spare.toString());
> val = ft.toObject(field);
> }
> UnicodeUtil.UTF8toUTF16 is called on our byte array,which isn't actually
> UTF8. I did a hack where I specified our own field comparator to be
> ByteBuffer based to get around that instanceof check, but then the field
> value gets transformed into BYTEARR in JavaBinCodec, and when it's
> unmarshalled, it gets turned into byte[]. Then, in QueryComponent.mergeIds, a
> ShardFieldSortedHitQueue is constructed with ShardDoc.getCachedComparator,
> which decides to give me comparatorNatural in the else of the TODO for
> CUSTOM, which barfs because byte[] are not Comparable...
> From Chris Hostetter:
> I'm not very familiar with the distributed sorting code, but based on your
> comments, and a quick skim of the functions you pointed to, it definitely
> seems like there are two problems here for people trying to implement
> custom sorting in custom FieldTypes...
> 1) QueryComponent.doFieldSortValues - this definitely seems like it should
> be based on the FieldType, not an "instanceof BytesRef" check (oddly: the
> comment event suggestsion that it should be using the FieldType's
> indexedToReadable() method -- but it doesn't do that. If it did, then
> this part of hte logic should work for you as long as your custom
> FieldType implemented indexedToReadable in a sane way.
> 2) QueryComponent.mergeIds - that TODO definitely looks like a gap that
> needs filled. I'm guessing the sanest thing to do in the CUSTOM case
> would be to ask the FieldComparatorSource (which should be coming from the
> SortField that the custom FieldType produced) to create a FieldComparator
> (via newComparator - the numHits & sortPos could be anything) and then
> wrap that up in a Comparator facade that delegates to
> FieldComparator.compareValues
> That way a custom FieldType could be in complete control of the sort
> comparisons (even when merging ids).
> ...But as i said: i may be missing something, i'm not super familia with
> that code. Please try it out and let us know if thta works -- either way
> please open a Jira pointing out the problems trying to implement
> distributed sorting in a custom FieldType.
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