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https://issues.apache.org/jira/browse/LUCENE-5702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14202739#comment-14202739
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David Smiley commented on LUCENE-5702:
--------------------------------------
bq. Maybe you could extend an existing FieldComparator to pull a
NumericDocValues instance differently (or IntValues/LongValues/... on 4.x) like
SortedNumericSortField does?
I considered that but FieldComparator.LongComparator's constructor is package
private, so that's a deal-breaker. In trunk (and 5x?) it's public.
In addition, to handle a more generic case, it's problematic because there's a
FieldCache/DV lookup *and* a Bits docsWithField lookup (and this logic is
annoyingly repeated several times). See the snippet below. In my case, I'm
sorting indirectly by looking up values in another document and so I need to
map the current doc id to a target id. I certainly don't want that to happen
twice for the same document (both the FieldCache/DV lookup *and* the
docsWithField call). The following logic could be extracted into a method that
a subclass could override, like hypothetical method getValue(doc):
{code:java}
long v2 = currentReaderValues.get(doc);
// Test for v2 == 0 to save Bits.get method call for
// the common case (doc has value and value is non-zero):
if (docsWithField != null && v2 == 0 && !docsWithField.get(doc)) {
v2 = missingValue;
}
{code}
Two examples of a FieldComparator instances in Lucene that could benefit from
some re-usable base classes are ExpressionComparator and ValueSourceComparator.
There are probably others.
> Per-segment comparator API
> --------------------------
>
> Key: LUCENE-5702
> URL: https://issues.apache.org/jira/browse/LUCENE-5702
> Project: Lucene - Core
> Issue Type: New Feature
> Reporter: Adrien Grand
> Assignee: Adrien Grand
> Priority: Minor
> Fix For: Trunk
>
> Attachments: LUCENE-5702.patch
>
>
> As a next step of LUCENE-5527, it would be nice to have per-segment
> comparators, and maybe even change the default behavior of our top*
> comparators so that they merge top hits in the end.
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