International Business Machines Corporation
PREVENTING DBMS DEADLOCK BY ELIMINATING SHARED LOCKING

Abstract:

A DBMS receives a database-access request that includes an instruction to non-destructively read a database table row. The DBMS assigns the request a TSN identifier and creates a TSN image that identifies all TSNs assigned to transactions that are not yet committed. The DBMS traverses a linked list of log entries that identifies a chronological history of transactions performed on the same row. The DBMS infers that the table row currently contains data stored by the most recently logged transaction that is not contained in the TSN image and that has thus been committed. The DBMS then continues to process statements of the transaction based on the assumption that the row contains the inferred value. The DBMS performs this procedure without acquiring a shared lock on the data page or on the index leaf page that points to the table row.