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From "Ning Li (JIRA)" <>
Subject [jira] Commented: (LUCENE-1035) Optional Buffer Pool to Improve Search Performance
Date Mon, 29 Oct 2007 23:41:51 GMT


Ning Li commented on LUCENE-1035:

> The question is whether such situations are common enough to warrant adding this to the


> A way around that might be to layer it on top of FSDirectory and add it to contrib.

I'd be happy to do that. I'll also include the following in the javadoc which hopefully is
a fair assessment:

"When will a buffer pool help:
  - When an index is significantly larger than the file system cache, the hit ratio of a buffer
pool is probably low which means insignificant performance improvement.
  - When an index is about the size of the file system cache or smaller, a buffer pool with
good enough hit ratio will help if the IO system calls are the bottleneck. An example is if
you have many "AND" queries which causes a lot large skips."

> Optional Buffer Pool to Improve Search Performance
> --------------------------------------------------
>                 Key: LUCENE-1035
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Store
>            Reporter: Ning Li
>         Attachments: LUCENE-1035.patch
> Index in RAMDirectory provides better performance over that in FSDirectory.
> But many indexes cannot fit in memory or applications cannot afford to
> spend that much memory on index. On the other hand, because of locality,
> a reasonably sized buffer pool may provide good improvement over FSDirectory.
> This issue aims at providing such an optional buffer pool layer. In cases
> where it fits, i.e. a reasonable hit ratio can be achieved, it should provide
> a good improvement over FSDirectory.

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