Proposal: introduce more sensible sorting when a doc has multiple values for a
term
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Key: LUCENE-1372
URL: https://issues.apache.org/jira/browse/LUCENE-1372
Project: Lucene - Java
Issue Type: Improvement
Components: Search
Affects Versions: 2.3.2
Reporter: Paul Cowan
Priority: Minor
At the moment, FieldCacheImpl has somewhat disconcerting values when sorting on
a field for which multiple values exist for one document. For example, imagine
a field "fruit" which is added to a document multiple times, with the values as
follows:
doc 1: {"apple"}
doc 2: {"banana"}
doc 3: {"apple", "banana"}
doc 4: {"apple", "zebra"}
if one sorts on the field "fruit", the loop in
FieldCacheImpl.stringsIndexCache.createValue() (and similarly for the other
methods in the various FieldCacheImpl caches) does the following:
while (termDocs.next()) {
retArray[termDocs.doc()] = t;
}
which means that we look over the terms in their natural order and, on each
one, overwrite retArray[doc] with the value for each document with that term.
Effectively, this overwriting means that a string sort in this circumstance
will sort by the LAST term lexicographically, so the docs above will
effecitvely be sorted as if they had the single values ("apple", "banana",
"banana", "zebra") which is nonintuitive. To change this to sort on the first
time in the TermEnum seems relatively trivial and low-overhead; while it's not
perfect (it's not local-aware, for example) the behaviour seems much more
sensible to me. Interested to see what people think.
Patch to follow.
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