static DatanodeInfo chooseDatanode(
final NameNode namenode,
final String path,
final HttpOpParam.Op op,
final long openOffset,
final long blocksize,
Configuration conf)
throws IOException {
final BlockManager bm = namenode.getNamesystem().getBlockManager();
if (op == PutOpParam.Op.CREATE) {
// choose a datanode near to client
final DatanodeDescriptor clientNode =
bm.getDatanodeManager().getDatanodeByHost(getRemoteAddress());
if (clientNode != null) {
final DatanodeDescriptor[] datanodes =
bm.getBlockPlacementPolicy().chooseTarget(path, 1, clientNode, null, blocksize);
if (datanodes.length > 0) {
return datanodes[0];
}
}
} else if (op == GetOpParam.Op.OPEN
|| op == GetOpParam.Op.GETFILECHECKSUM
|| op == PostOpParam.Op.APPEND) {
// choose a datanode containing a replica
final NamenodeProtocols np = namenode.getRpcServer();
final HdfsFileStatus status = np.getFileInfo(path);
if (status == null) {
throw new FileNotFoundException("File " + path + " not found.");
}
final long len = status.getLen();
if (op == GetOpParam.Op.OPEN) {
if (openOffset < 0L || (openOffset >= len && len > 0)) {
throw new IOException(
"Offset="
+ openOffset
+ " out of the range [0, "
+ len
+ "); "
+ op
+ ", path="
+ path);
}
}
if (len > 0) {
final long offset = op == GetOpParam.Op.OPEN ? openOffset : len - 1;
final LocatedBlocks locations = np.getBlockLocations(path, offset, 1);
final int count = locations.locatedBlockCount();
if (count > 0) {
return JspHelper.bestNode(locations.get(0).getLocations(), false, conf);
}
}
}
return (DatanodeDescriptor)
bm.getDatanodeManager().getNetworkTopology().chooseRandom(NodeBase.ROOT);
}
