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From "Patrick Johnstone" <pjohnst...@dejavunet.net>
Subject Order of fields returned by Document.getFields()
Date Tue, 16 Dec 2008 15:00:25 GMT

I'm using Lucene via Solr and recently upgraded from an early Summer nightly
build to the released version of Solr 1.3 (which seems to use something in
the neighborhood of Lucene 2.3).  I'm posting this here because I believe
that my issue is with Lucene, not Solr.

After the upgrade, I noticed that the order of fields being returned for
documents had changed.  Previously, the order of fields being returned was
the same as the order in which they were added to the document (which is
what's stated in the FAQ and other places I came across but not specifically
spelled out in the Javadoc).
Now, the fields always seem to come back in lexicographic order by field
name.

I believe (but am by no means sure) that this is being caused by the
following bit of code in DocFieldProcessorPerThread.java:

    // If we are writing vectors then we must visit
    // fields in sorted order so they are written in
    // sorted order.  TODO: we actually only need to
    // sort the subset of fields that have vectors
    // enabled; we could save [small amount of] CPU
    // here.
    quickSort(fields, 0, fieldCount-1);

    for(int i=0;i<fieldCount;i++)
      fields[i].consumer.processFields(fields[i].fields,
fields[i].fieldCount);

This code seems to sort the fields of the document into order before
processing them.  If this is true, then the original field order is lost and
can't ever be recovered.  (None of the fields in our index use TermVectors.)

My questions are:  Is my reading of this behavior correct?  ...and...
if so:  Is there some other way to get the original order back?

The application that I'm building took some advantage of the fact that the
fields were returned in the orignial order (becuase the order had some
meaning) and it may be difficult for me to work around this change.

Patrick Johnstone
DejaVu Networks
pjohnstone@dejavunet.net


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