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From "Andrzej Bialecki (JIRA)" <>
Subject [jira] Commented: (NUTCH-455) dedup on tokenized fields is faulty
Date Fri, 06 Feb 2009 13:52:04 GMT


Andrzej Bialecki  commented on NUTCH-455:

Since LUCENE-252 is still unresolved, and it's not clear which of the proposed solutions should
be selected, I'm postponing this issue.

> dedup on tokenized fields is faulty
> -----------------------------------
>                 Key: NUTCH-455
>                 URL:
>             Project: Nutch
>          Issue Type: Bug
>          Components: searcher
>    Affects Versions: 0.9.0
>            Reporter: Enis Soztutar
>             Fix For: 1.1
>         Attachments: IndexSearcherCacheWarm.patch
> (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,
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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