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https://issues.apache.org/jira/browse/LUCENE-753?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12550376
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Brian Pinkerton commented on LUCENE-753:
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BTW, I think the performance win with Yonik's patch for some workloads could be
far greater than what the simple benchmark illustrates. Sure, pread might be
marginally faster. But the real win is avoiding synchronized access to the
file.
I did some IO tracing a while back on one particular workload that is
characterized by:
* a small number of large compound indexes
* short average execution time, particularly compared to disk response time
* a 99+% FS cache hit rate
* cache misses that tend to cluster on rare queries
In this workload where each query hits each compound index, the locking in
FSIndexInput means that a single rare query clobbers the response time for all
queries. The requests to read cached data are serialized (fairly, even) with
those that hit the disk. While we can't get rid of the rare queries, we can
allow the common ones to proceed against cached data right away.
> Use NIO positional read to avoid synchronization in FSIndexInput
> ----------------------------------------------------------------
>
> Key: LUCENE-753
> URL: https://issues.apache.org/jira/browse/LUCENE-753
> Project: Lucene - Java
> Issue Type: New Feature
> Components: Store
> Reporter: Yonik Seeley
> Attachments: FileReadTest.java, FileReadTest.java,
> FSIndexInput.patch, FSIndexInput.patch
>
>
> As suggested by Doug, we could use NIO pread to avoid synchronization on the
> underlying file.
> This could mitigate any MT performance drop caused by reducing the number of
> files in the index format.
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