[HDFS-13978] Review of DiskBalancer

• Type: Improvement
• Status: Patch Available
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 3.2.0
• Component/s: datanode, hdfs
• Flags: Patch
• Assignee: David Mollitor
• Reporter: David Mollitor
• Created: 09/Oct/18 14:25
• Updated: 15/Oct/18 14:57

Description

• Use ArrayList instead of LinkedList. Especially because this code here uses the List#get() method, which is very slow for the LinkedList since it has to traverse every node to get to the offset: O(N^2)

    ExtendedBlock getNextBlock(List<FsVolumeSpi.BlockIterator> poolIters,
                               DiskBalancerWorkItem item) {
      Preconditions.checkNotNull(poolIters);
      int currentCount = 0;
      ExtendedBlock block = null;
      while (block == null && currentCount < poolIters.size()) {
        currentCount++;
        int index = poolIndex++ % poolIters.size();
        FsVolumeSpi.BlockIterator currentPoolIter = poolIters.get(index);
        block = getBlockToCopy(currentPoolIter, item);
      }

• Do not "log and throw" errors. This is an anti-pattern and should be avoided. Log or throw, but don't do both. Removed some logging
• Improved other logging statements
• Improved the hashcode method of one of the inner classes. It was instantiating a List and performing iteration for every call. Replace with Eclipse-generated hashcode method.
• Fixed compiler warnings for deprecated code or code that was not parameterized
• Fix check style issue