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https://issues.apache.org/jira/browse/HBASE-10320?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Lars Hofhansl resolved HBASE-10320.
-----------------------------------
Resolution: Fixed
Hadoop Flags: Reviewed
Committed to all branches. Thanks for the reviews, and especially to [~eclark]
for the benchmarking.
> Avoid ArrayList.iterator() ExplicitColumnTracker
> ------------------------------------------------
>
> Key: HBASE-10320
> URL: https://issues.apache.org/jira/browse/HBASE-10320
> Project: HBase
> Issue Type: Bug
> Components: Performance
> Reporter: Lars Hofhansl
> Assignee: Lars Hofhansl
> Fix For: 0.98.0, 0.96.2, 0.99.0, 0.94.17
>
> Attachments: 10320-0.94-v2.txt, 10320-0.94-v3.txt, 10320-0.94-v4.txt,
> 10320-0.94.txt, 10320-trunk-v4.txt
>
>
> I noticed that in a profiler (sampler) run ScanQueryMatcher.setRow(...)
> showed up at all.
> In turns out that the expensive part is iterating over the columns in
> ExcplicitColumnTracker.reset(). I did some microbenchmarks and found that
> {code}
> private ArrayList<X> l;
> ...
> for (int i=0; i<l.size(); i++) {
> X = l.get(i);
> ...
> }
> {code}
> Is twice as fast as:
> {code}
> private ArrayList<X> l;
> ...
> for (X : l) {
> ...
> }
> {code}
> The indexed version asymptotically approaches the iterator version, but even
> at 1m entries it is still faster.
> In my tight loop scans this provides for a 5% performance improvement overall
> when the ExcplicitColumnTracker is used.
> Edit:
> {code}
> private X[] l;
> ...
> for (int i=0; i<l.length; i++) {
> X = l[i];
> ...
> }
> {code}
> Is even better. Apparently the JVM can even save the boundary check in each
> iteration.
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