[HBASE-22504] Optimize the MultiByteBuff#get(ByteBuffer, offset, len) - ASF JIRA

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Details

Type: Sub-task
Status: Closed
Priority: Major
Resolution: Fixed
Affects Version/s: None
Fix Version/s: 3.0.0-alpha-1, 2.3.0
Component/s: BucketCache
Labels:
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Hadoop Flags:

Reviewed

Description

In ~~HBASE-22483~~, we saw that the BucketCacheWriter thread was quite busy [^BucketCacheWriter-is-busy.png], the flame graph also indicated that the ByteBufferArray#internalTransfer cost ~6% CPU (see async-prof-pid-25042-cpu-1.svg). because we used the hbase.ipc.server.allocator.buffer.size=64KB, each HFileBlock will be backend by a MultiByteBuff: one 64KB offheap ByteBuffer and one small heap ByteBuffer.

The path is depending on the MultiByteBuff#get(ByteBuffer, offset, len) now:

RAMQueueEntry#writeToCache
    |--> ByteBufferIOEngine#write
        |--> ByteBufferArray#internalTransfer
            |--> ByteBufferArray$WRITER
                |--> MultiByteBuff#get(ByteBuffer, offset, len)

While the MultiByteBuff#get impl is simple and crude now, can optimze this implementation:

  @Override
  public void get(ByteBuffer out, int sourceOffset,
      int length) {
    checkRefCount();
      // Not used from real read path actually. So not going with
      // optimization
    for (int i = 0; i < length; ++i) {
      out.put(this.get(sourceOffset + i));
    }
  }