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From Li Li <>
Subject Re: combine results from multiple queries & sort
Date Wed, 14 Mar 2012 10:44:33 GMT
it's a very common problem. many of our users(including programmers that
familiar with sql) have the same question.

comparing with sql, all queries in lucene are based on inverted index.
fortunately, when searching, we can providing a Filter.

from source codes of function searchWithFilter
we can see searching is similar to boolean and queries.

I think you can use TermsFilter.
it just iterator through the terms(your ids) and use BitSet to do filter.
if the documents contains any of the words, it's set to 1, otherwise is 0.

I think this implementation is fast enough, it use tii/tis to locate words,
and for each words, it iterate through it's postings by frq file. postings
may be cached by lucene.

If it can't meet your performance needs. you can implement your own
Collector and using your own cache policy(maybe load all this fields into
memory by a hashmap  your ids->document id)
when a query is "id in(1,3,5,)", you construct a Collector. when it
collects docs, you filter unwanted documents

On Wed, Mar 14, 2012 at 4:01 PM, Jamie <> wrote:

> Greetings!
> First off, I realize Lucene is a search engine and therefore does not
> possess many of the features of a database. That being said, I have
> encountered a particular use case where I need to lookup potentially
> thousands of records in a Lucene index based upon an ID (a String field in
> the index). This data also needs be sorted based upon any chosen field in
> the index. In pseudo code, this is how its currently done:
> String[] ids = { "123aeeff", "34eacc", ...}
> results.clear();
> StringBuffer lookupQuery = new StringBuffer()
> for (int i=0; i<ids.size();i++) {
>       lookupQuery.append(ids.get(i))
>       lookupQuery.append(" ")
>        if ((i+1) % 1024 == 0) {
>            search(lookupQuery.toString())
>             lookupQuery = new StringBuffer()
>       }
>  }
> if (lookupQuery.length()>0) {
>        search(lookupQuery.toString())
> }
> As you can see, in a loop, Lucene queries are constructed into a maximum
> of 1024 terms, for example, consisting of IDS "123aeeff 34eacc ..". After
> each query in the loop is constructed, a search is executed and then the
> results are combined into a single linkedlist (this is done in the search
> function). This works well aside from two outstanding questions:
> 1. Is executing separate search queries, the best way to lookup
>   thousands of records in an index? Is there a more efficient way to
>   lookup thousands of records based upon ID?
> 2. The results are unsorted after they are combined into a single
>   linkedlist. What is the best way to sort the combined results based
>   upon any chosen field in the lucene index? Is there a way to do that
>   would leverage Lucene's inbuilt sort abilities?
> Many thanks for your consideration
> Jamie

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