An open and safe nested transaction model: concurrency and recovery

Abstract

In this paper, we present an open and safe nested transaction model. We discuss the concurrency control and recovery algorithms for our model. Our nested transaction model uses the notion of a recovery point subtransaction in the nested transaction tree. It incorporates a prewrite operation before each write operation to increase the potential concurrency. Our transaction model is termed``open and safe'' as prewrites allow early reads (before writes are performed on disk) without cascading aborts. The systems restart and buer management operations are also modeled as nested transactions to exploit possible concurrency during restart. The concurrency control algorithm proposed for database operations is also used to control concurrent recovery operations. We have given a snapshot of complete transaction processing, data structures involved and, building the restart state in case of crash recovery. Ó

Scheduling Distributed Real-Time Nested Transactions

“…The main types of nested transaction models are (1) closed nested transaction [12] and (2) open nested transaction [17]. In the closed nested transaction model [1,12,9,5], a subtransaction's effect cannot be seen outside its parent's view.…”

“…In the closed nested transaction model [1,12,9,5], a subtransaction's effect cannot be seen outside its parent's view. In this model, originally introduced by Moss [12], a commitment of a subtransaction is conditional upon the commitments of its parent, while in the open nested transaction model [17], the subtransactions can execute and commit independently. The leaf level locks are released early only if the semantics of the operations is known.…”