Kannan Muthukkaruppan created HBASE-6066:
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Summary: some low hanging read path improvement ideas
Key: HBASE-6066
URL: https://issues.apache.org/jira/browse/HBASE-6066
Project: HBase
Issue Type: Bug
Reporter: Kannan Muthukkaruppan
I was runnign some single threaded scan performance tests for a table
with small sized rows that is fully cached. Some observations...
Several wasteful iterations over and/or building of temporary lists.
1) One such is the following:
{code}
boolean moreRows = s.next(values, HRegion.METRIC_NEXTSIZE);
if (!values.isEmpty()) {
for (KeyValue kv : values) { ------> #### wasteful in most
cases
currentScanResultSize += kv.heapSize();
}
results.add(new Result(values));
{code}
By default the "maxScannerResultSize" is Long.MAX_VALUE. In those cases,
avoid the unnecessary iteration to compute currentScanResultSize.
2) An example of a wasteful temporary array, is "results" in
RegionScanner.next().
{code}
results.clear();
boolean returnResult = nextInternal(limit, metric);
outResults.addAll(results);
{code}
results then gets copied over to outResults via an addAll().
Not sure why we can directly collect the results in outResults.
3) Another almost similar exmaple of a wasteful array is "results" in
StoreScanner.next(), which eventually also copies its results
into "outResults".
4) Reduce overhead of "size metric" maintained in StoreScanner.next().
{code}
if (metric != null) {
HRegion.incrNumericMetric(this.metricNamePrefix + metric,
copyKv.getLength());
}
results.add(copyKv);
{code}
A single call to next() might fetch a lot of KVs. We can first add up the size
of those KVs in a local variable and then in a finally clause increment the
metric one shot, rather than updating AtomicLongs for each KV.
5) RegionScanner.next() calls a helper RegionScanner.next() on the same object.
Both are synchronized methods. Synchronized methods calling nested synchronized
methods on the same object are probably adding some small overhead. The inner
next() calls isFilterDone() which is a also a synchronized method. We should
factor the code to avoid these nested synchronized methods.
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