FSImageSerialization.java 文件源码

/**
 * Write an array of blocks as compactly as possible. This uses
 * delta-encoding for the generation stamp and size, following
 * the principle that genstamp increases relatively slowly,
 * and size is equal for all but the last block of a file.
 */
public static void writeCompactBlockArray(
    Block[] blocks, DataOutputStream out) throws IOException {
  WritableUtils.writeVInt(out, blocks.length);
  Block prev = null;
  for (Block b : blocks) {
    long szDelta = b.getNumBytes() -
        (prev != null ? prev.getNumBytes() : 0);
    long gsDelta = b.getGenerationStamp() -
        (prev != null ? prev.getGenerationStamp() : 0);
    out.writeLong(b.getBlockId()); // blockid is random
    WritableUtils.writeVLong(out, szDelta);
    WritableUtils.writeVLong(out, gsDelta);
    prev = b;
  }
}