@Override
  public String toString() {
    StringBuilder sb = new StringBuilder(1024);
    for (int i = 0; i < buckets.length; ++i) {
      Bucket b = buckets[i];
      if (i > 0) sb.append(", ");
      sb.append("bucket.").append(i).append(": size=").append(b.getItemAllocationSize());
      sb.append(", freeCount=").append(b.freeCount()).append(", used=").append(b.usedCount());
    }
    return sb.toString();
  }
Rebuild the allocator's data structures from a persisted map.
@param availableSpace capacity of cache
@param map            A map stores the block key and BucketEntry(block's meta data like offset,
                      length)
@param realCacheSize  cached data size statistics for bucket cache
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketAllocator.java