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https://issues.apache.org/jira/browse/HDFS-14541?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Work on HDFS-14541 started by Lisheng Sun.
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> ShortCircuitReplica#unref cost about 6% cpu and 6% heap allocation because of
> the frequent thrown NoSuchElementException in our HBase benchmark
> ------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-14541
> URL: https://issues.apache.org/jira/browse/HDFS-14541
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Zheng Hu
> Assignee: Lisheng Sun
> Priority: Major
> Attachments: HDFS-14541.000.patch, after-QPS.png,
> after-cpu-flame-graph.svg, after-heap-flame-graph.svg,
> async-prof-pid-94152-alloc-2.svg, async-prof-pid-94152-cpu-1.svg,
> before-QPS.png, before-cpu-flame-graph.svg, before-heap-flame-graph.svg
>
>
> Our XiaoMi HBase team are evaluating the performence improvement of
> HBASE-21879, and we have few CPU flame graph & heap flame graph by using
> async-profiler, and find that there're some performence issues in DFSClient
> .
> See the attached two flame graphs, we can conclude that the try catch block
> in ShortCircuitCache#trimEvictionMaps has some serious perf problem , we
> should remove the try catch from DFSClient.
> {code}
> /**
> * Trim the eviction lists.
> */
> private void trimEvictionMaps() {
> long now = Time.monotonicNow();
> demoteOldEvictableMmaped(now);
> while (true) {
> long evictableSize = evictable.size();
> long evictableMmappedSize = evictableMmapped.size();
> if (evictableSize + evictableMmappedSize <= maxTotalSize) {
> return;
> }
> ShortCircuitReplica replica;
> try {
> if (evictableSize == 0) {
> replica = (ShortCircuitReplica)evictableMmapped.get(evictableMmapped
> .firstKey());
> } else {
> replica = (ShortCircuitReplica)evictable.get(evictable.firstKey());
> }
> } catch (NoSuchElementException e) {
> break;
> }
> if (LOG.isTraceEnabled()) {
> LOG.trace(this + ": trimEvictionMaps is purging " + replica +
> StringUtils.getStackTrace(Thread.currentThread()));
> }
> purge(replica);
> }
> }
> {code}
> Our Xiaomi HDFS Team member [~leosun08] will prepare patch for this issue.
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