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From "Adam Fuchs (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-3079) improve system iterator performance by collapsing call stack
Date Tue, 02 Sep 2014 18:44:21 GMT


Adam Fuchs commented on ACCUMULO-3079:

[~elserj] In this patch I moved the synchronization to the filter, so the functionality is
still there. Along the way, I did play around with removing the SyncronizedIterator altogether
in the case where no client iterators are present. I didn't take specific performance measurements
isolating that change, so I'm not sure if it's more than the order of 1% referenced in ACCUMULO-533.
However, it does shorten the stack, which seems to be related to the funkiness around ACCUMULO-3067.
I could subjectively say that the performance difference between not having the Synchronized
iterator at all and moving its functionality into the VisibilityFilter was small enough to
be hidden in the testing noise, but I don't have evidence to objectively state that.

> 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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