Method and apparatus of enforcing uniqueness of a key value for a row in a data table

摘要

In a database table with rows each having respective key values, the locking of a key value to enforce key-value uniqueness is accomplished by (a) mapping the key value into a set of hash values to produce a resulting hash value, and (b) locking all key values (i.e., preventing writing of key values in new rows and preventing updates creating new key values in existing rows) that map into the resulting hash value. This provides a compromise between the high-granularity and high-cost solution of indexing, and the low-cost but very low-granularity solution of table-level locking. One useful application of this technique lies in the enforcement of uniqueness of multi-column keys in the table without incurring the cost of indexing all possible combinations of column values that might comprise key values.