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From "Trejkaz (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-893) Increase buffer sizes used during searching
Date Wed, 25 Feb 2009 06:07:01 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-893?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12676521#action_12676521
] 

Trejkaz commented on LUCENE-893:
--------------------------------

Someone else on my team did some benchmarks for a query which was slow for us.

We have a tree of items (one item per document), and given N items, we walk the path from
the root to the item until finding an item with certain properties (expected average queries
per item is around 3.)  All the queries are against the same field (our unique ID field.)

Timings of this process for 60,000 items:

Buffer size	Time
1024	1015s
2048	540s
4096	335s
8196	281s
16384	278s
32768	284s
65536	322s



> Increase buffer sizes used during searching
> -------------------------------------------
>
>                 Key: LUCENE-893
>                 URL: https://issues.apache.org/jira/browse/LUCENE-893
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Search
>    Affects Versions: 2.1
>            Reporter: Michael McCandless
>
> Spinoff of LUCENE-888.
> In LUCENE-888 we increased buffer sizes that impact indexing and found
> substantial (10-18%) overall performance gains.
> It's very likely that we can also gain some performance for searching
> by increasing the read buffers in BufferedIndexInput used by
> searching.
> We need to test performance impact to verify and then pick a good
> overall default buffer size, also being careful not to add too much
> overall HEAP RAM usage because a potentially very large number of
> BufferedIndexInput instances are created during searching
> (# segments X # index files per segment).

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