Lucene now has an in-memory terms dictionary…

Lucene now has an in-memory terms dictionary, thanks to Google Summer of Code by Mike McCandless.

From the post:

Last year, Han Jiang’s Google Summer of Code project was a big success: he created a new (now, default) postings format for substantially faster searches, along with smaller indices.

This summer, Han was at it again, with a new Google Summer of Code project with Lucene: he created a new terms dictionary holding all terms and their metadata in memory as an FST.

In fact, he created two new terms dictionary implementations. The first, FSTTermsWriter/Reader, hold all terms and metadata in a single in-memory FST, while the second, FSTOrdTermsWriter/Reader, does the same but also supports retrieving the ordinal for a term (TermsEnum.ord()) and looking up a term given its ordinal (TermsEnum.seekExact(long ord)). The second one also uses this ord internally so that the FST is more compact, while all metadata is stored outside of the FST, referenced by ord.

Lucene continues to improve, rapidly!

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