dedup on tokenized fields is faulty
-----------------------------------
Key: NUTCH-455
URL: https://issues.apache.org/jira/browse/NUTCH-455
Project: Nutch
Issue Type: Bug
Components: searcher
Affects Versions: 0.9.0
Reporter: Enis Soztutar
Fix For: 0.9.0
(From LUCENE-252)
nutch uses several index servers, and the search results from these servers are
merged using a dedup field for for deleting duplicates. The values from this
field is cached by Lucene's FieldCachImpl. The default is the site field, which
is indexed and tokenized. However for a Tokenized Field (for example "url" in
nutch), FieldCacheImpl returns an array of Terms rather that array of field
values, so dedup'ing becomes faulty. Current FieldCache implementation does not
respect tokenized fields , and as described above caches only terms.
So in the situation that we are searching using "url" as the dedup field, when
a Hit is constructed in IndexSearcher, the dedupValue becomes a token of the
url (such as "www" or "com") rather that the whole url. This prevents using
tokenized fields in the dedup field.
I have written a patch for lucene and attached it in
http://issues.apache.org/jira/browse/LUCENE-252, this patch fixes the
aforementioned issue about tokenized field caching. However building such a
cache for about 1.5M documents takes 20+ secs. The code in
IndexSearcher.translateHits() starts with
if (dedupField != null)
dedupValues = FieldCache.DEFAULT.getStrings(reader, dedupField);
and for the first call of search in IndexSearcher, cache is built.
Long story short, i have written a patch against IndexSearcher, which in
constructor warms-up the caches of wanted fields(configurable). I think we
should vote for LUCENE-252, and then commit the above patch with the last
version of lucene.
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