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From "Josh Elser (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-3079) improve system iterator performance by collapsing call stack
Date Tue, 02 Sep 2014 18:16:21 GMT


Josh Elser commented on ACCUMULO-3079:

I just stumbled on trying to figure out exactly what the SynchronizedIterator does (to document
it) and noticed that you also made changes here to try to alleviate the extra iterator in
the stack. I'm wondering if it makes sense to keep that synchronized filter in the stack during
normal cases anyways? Most times, I don't think Iterators really lend themselves well to doing
multi-threaded operations anyways. I see in ACCUMULO-533 when you added the SynchronizedIterator,
you didn't see any performance impact. I'm wondering if it would make sense to add an option
to the client API that allows configuration of the SynchronizedIterator (or the filter as
your patch changes it to be). Thoughts?

> improve system iterator performance by collapsing call stack
> ------------------------------------------------------------
>                 Key: ACCUMULO-3079
>                 URL:
>             Project: Accumulo
>          Issue Type: Improvement
>            Reporter: Adam Fuchs
>            Assignee: Adam Fuchs
>             Fix For: 1.6.1, 1.7.0
>         Attachments: iterator_performance_20140822_1.patch, iterator_performance_test_harness.tar.gz
> System iterators are at the core of the tightest loops in Accumulo, handling every key/value
pair that traverses through a scan or a compaction. In many cases, iterators are the current
performance bottleneck for Accumulo. Every bit that we can improve performance in the iterators
translates into better performance for Accumulo.
> There are several strategies that can be applied to the current code base to improve
performance, including:
>  # Inlining calls that are hard for the JVM to inline at runtime
>  # Moving checks for null outside of tight loops when they are invariants within the
>  # Eliminating "no-op" iterators at iterator tree construction time
>  # Making frequently used and assigned-once objects final (like iterator sources)

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