//search key2root first
Integer idocID = new Integer(docID);
PageNumber subRoot = (PageNumber) id2root.get(idocID);
if (subRoot == null) {
Key tmpKey = new IntKey(docID);
indexBTree.acquire(kContext, READ_MODE);
byte[] bRoot = null;
try {
bRoot = (byte[]) indexBTree.lookup(tmpKey, kContext);
} finally {