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From Adrien Grand <jpou...@gmail.com>
Subject Re: Increase search performance
Date Wed, 31 Jan 2018 13:03:13 GMT
Hi Atul,


Le mar. 30 janv. 2018 à 16:24, Atul Bisaria <atul.bisaria@ericsson.com> a
écrit :

> 1.     Using ConstantScoreQuery so that scoring overhead is removed since
> scoring is not required in my search use case. I also use a custom Sort
> object which does not sort by score (see code below).
>

If you don't sort by score, then wrapping with a ConstantScoreQuery won't
help as Lucene will figure out scores are not needed anyway.


> 2.     Using query cache
>
>
>
> My understanding is that query cache would cache query results and hence
> lead to significant increase in performance. Is this understanding correct?
>

It depends what you mean by performance. If you are optimizing for
worst-case latency, then the query cache might make things worse due to the
fact that caching a query requires to visit all matches, while query
execution can sometimes just skip over non-interesting matches (eg. in
conjunctions).

However if you are looking at improving throughput, then usually the
default policy of the query cache of caching queries that look reused
usually helps.


> I am using Lucene version 5.4.1 where query cache seems to be enabled by
> default (https://issues.apache.org/jira/browse/LUCENE-6784), but I am not
> able to see any significant change in search performance.
>




> Here is the code I am testing with:
>
>
>
> DirectoryReader reader = DirectoryReader.open(directory);      //using
> MMapDirectory
>
> IndexSearcher searcher = new IndexSearcher(reader);
> //IndexReader and IndexSearcher are created only once
>
> searcher.setQueryCachingPolicy(QueryCachingPolicy.ALWAYS_CACHE);
>

Don't do that, this will always cache all filters, which usually makes
things slower for the reason mentioned above. I would rather advise that
you use an instance of UsageTrackingQueryCachingPolicy.

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