Deadlock-freedom of large transactions in object management systems

摘要

Different sorts of large transactions can be found in object management systems, i.e. databases for engineering design systems. Examples are design transactions, tool executions and operations on complex objects. Such transactions should not run into deadlocks because their rollback is very expensive.We propose a solution which is based on two-phase locking with pseudo-preclaiming, a variant of preclaiming, in which locks are acquired concurrently with the running transaction. One main problem is to find a deadlock-free lock acquistion strategy which has the “immediate granting property”; this means that locks which are requested on unlocked objects are granted immediately. We show the queue protocol has this property.Finally, we show how deadlocks can be prevented, or made, at least, less probable, if further locks are requested after the preclaiming operation or if navigation is required to determine the set of objects used by a transaction.