[jira] [Created] (HDFS-16639) LightWeightHashSet.resize possibly quadratic behavior could affect performance

["BugFinder (Jira)" <ji...@apache.org>]

BugFinder created HDFS-16639:
--------------------------------

             Summary: LightWeightHashSet.resize possibly quadratic behavior could affect performance
                 Key: HDFS-16639
                 URL: https://issues.apache.org/jira/browse/HDFS-16639
             Project: Hadoop HDFS
          Issue Type: Test
          Components: hdfs
    Affects Versions: 3.0.0
            Reporter: BugFinder


Hi,

We have been performance profiling with our in-house tools a few versions of HDFS (including 3.0.0) and we have noticed some places for possible optimizations. According to what we have seen, the method 

org.apache.hadoop.hdfs.util.LightWeightHashSet.resize

has a possibly quadratic behavior (linear at the least) which might be impactful depending on which data is being stored in the instance (e.g. too many blocks to be removed like [here|https://issues.apache.org/jira/browse/HDFS-16574]). Albeit this behavior might be reasonable or even not noticeable in some cases, when under wide locks as in

FSNamesystem.reportBadBlocks *// Holding the write lock*
  BlockManager.findAndMarkBlockAsCorrupt
    BlockManager.markBlockAsCorrupt
     BlockManager.addToInvalidates
        InvalidateBlocks.add
          LightWeightHashSet.add
            LightWeightHashSet.expandIfNecessary
              LightWeightHashSet.resize

 

There are several call trees that seem to end in resize and have locks. Not all of these are bad or better said, not all of these are problematic in every workload. We do not have a proposal for a solution yet, as we are doing exploratory work with our in-house tools. We believe this issue is present not only in 3.0.0 but also in more recent versions. 



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