An open and safe nested transaction model: concurrency and recovery

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 bu€er 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 2000 Elsevier Science Inc. All rights reserved.