1. A method, implemented by a packet processing node in a packet-switched network, for performing a data lookup on a hash table, said method comprising: receiving a packet containing a flow identifier; generating a full search key from the flow identifier; determining a corresponding hash bucket in said hash table based on the full search key; creating a compressed search key from signature bits extracted from predetermined bit locations in the full search key; predicting a hash entry index for a target hash entry in the hash bucket by comparing the compressed search key to signature patterns that are mapped one-to-one to hash entries in the hash bucket, wherein the target hash entry comprises a hash key and associated data; and performing said data lookup by comparing the full search key to the hash key in the target hash entry.