HBase BucketAllocatorException 异常剖析

近日，观察到HBase集群出现如下WARN日志：

2020-04-18 16:17:03,081 WARN [regionserver/xxx-BucketCacheWriter-1] bucket.BucketCache:Failed allocation for 604acc82edd349ca906939af14464bcb_175674734; org.apache.hadoop.hbase.io.hfile.bucket.BucketAllocatorException: Allocation too big size=1114202; adjust BucketCache sizes hbase.bucketcache.bucket.sizes to accomodate if size seems reasonable and you want it cached.

大概意思是说：由于block块太大（size=1114202）导致BucketAllocator无法为其分配空间，如果想要被缓存并且觉得这样做合理，可以调整参数hbase.bucketcache.bucket.sizes。

默认情况下，HBase BucketCache 能够缓存block的大值为512KB，即hbase.bucketcache.bucket.sizes=5120,9216,17408,33792,41984,50176,58368,66560,99328,132096,197632,263168,394240,525312，默认14种size标签。如果想要缓存更大的block块，我们可以调整参数为 hbase.bucketcache.bucket.sizes=5120,9216,17408,33792,41984,50176,58368,66560,99328,132096,197632,263168,394240,525312,1049600,2098176，此时大容许2MB的block。

下面我们简单看一下对应源代码，涉及相关类为： /hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketAllocator.java BucketAllocator主要实现对bucket的组织管理，为block分配内存空间。

/**
   * Allocate a block with specified size. Return the offset
   * @param blockSize size of block
   * @throws BucketAllocatorException
   * @throws CacheFullException
   * @return the offset in the IOEngine
   */
  public synchronized long allocateBlock(int blockSize) throws CacheFullException,
      BucketAllocatorException {
    assert blockSize > 0;
    BucketSizeInfo bsi = roundUpToBucketSizeInfo(blockSize);
    if (bsi == null) {
      throw new BucketAllocatorException("Allocation too big size=" + blockSize +
        "; adjust BucketCache sizes " + BlockCacheFactory.BUCKET_CACHE_BUCKETS_KEY +
        " to accomodate if size seems reasonable and you want it cached.");
    }
    long offset = bsi.allocateBlock();

    // Ask caller to free up space and try again!
    if (offset < 0)
      throw new CacheFullException(blockSize, bsi.sizeIndex());
    usedSize += bucketSizes[bsi.sizeIndex()];
    return offset;
  }