System method and computer program product for dynamically sizing hash

Abstract

The present invention is a system, method, and computer program product for dynamically sizing a hash table when the average number of records per bucket in the hash table exceeds a maximum average number of records per bucket. In one embodiment, the hash table employs a modulo hashing function. In a second embodiment, the number of buckets is grown by a multiple of the previous number of buckets and records are re-hashed using a lazy re-hashing modulo algorithm that re-hashes records in a hash bucket only when those records are searched. In the second embodiment, when a hash table is re-sized, each new bucket is provided with a logical back pointer, or index, to a pre-existing bucket that potentially contains records that belong in the new bucket. When a search is directed at a new bucket, the logical back pointer, or index, directs the search to a pre-existing bucket. When a search of a pre-existing bucket finds a data record that belongs in a new bucket, the record is moved to the new bucket. When there are no more records in a pre-existing bucket that belong in a new bucket, the logical back pointer from the new bucket to the pre-existing bucket is removed. Preferably, the logical back pointer is stored in the bucket where a regular pointer would normally be stored so that no extra space is needed.