Atomic Objects for Real-Time Distributed Systems with Mixed Time Constraints

Two types of applications are considered: Hard Real-Time (HRT) and Soft Real-Time (SRT). HRT applications need to meet their deadlines under all circumstances; deadlines of SRT applications may occasionally be missed. Both applications are constructed from objects. HRT and SRT applications coexist on the same set of processors and share objects to allow a consistent exchange of data via transactions. Several concurrency control algorithms exist to assure consistent transaction results in distributed database systems. The addition of versions to objects can diminish the execution time of read-only transactions and increases the number of permitted inter-leavings of concurrently executing transactions. Imposing two diierent orderings, one for read-only transactions and one for all other transactions, the wait-time of read-only transactions is considerably reduced. Small delays increase the probability that SRT deadlines are met or a design is reached in which all HRT requirements are met. The interleaving of HRT-and SRT-transactions is severely reduced when SRT-transactions are not allowed to perturb HRT-transactions. The here deened transfer-serializability criterion permits the interleaving of HRT-and SRT-transactions.