Weak record locks in database query read processing

Abstract

A weak record locking scheme that, while enforcing serialization of record updates, permits a read to extract data from uncommitted updates. Specifically, records are locked in association with a process or thread performing a lock. When the records affected by a transaction are initially locked for reading or updating, they are locked at the process level. When a particular record is to be read or updated as part of a transaction, it is locked at the thread level. A read transaction that will accept uncommitted changes uses a weak lock to lock the record for reading. A weak lock may be made on a record so long as the record is not already locked for updating at the thread level. While a record is weakly locked for reading, it cannot be locked for updating at the thread level. A record may thus be weakly locked even though the record is locked for updating at the process level by the same process. Weak locking thus preserves serialization of updates, while reducing delays caused by locking conflicts.