Lars Hofhansl created HBASE-10320:
-------------------------------------
Summary: Avoid ArrayList.iterator() in tight loops
Key: HBASE-10320
URL: https://issues.apache.org/jira/browse/HBASE-10320
Project: HBase
Issue Type: Bug
Components: Performance
Reporter: Lars Hofhansl
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 than:
{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.
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