Resolution: Won't Fix
Affects Version/s: 0.9.0
Fix Version/s: None
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.