Efficient Commit/Abort Procedures in the RelaX Distributed Transaction Layer

Abstract

Transactions are especially valuable in distributed systems, since they isolate the programmer from the effects of both concurrency and failures. In implementing transactions at the system level, flexibility has to be introduced into the transaction concept. Especially, the premature release of objects has to be dealt with. To assure recoverability nevertheless, resulting dependencies between transactions are stored by the system in a distributed data structure called recovery graph. By partially replicating the recovery graph at the different sites, the complexity of the commit procedure is reduced and a chase procedure used to abort transactions can be derived which avoids infinite chasing. The information transfer needed for replication is almost for free because it can be piggybacked on messages sent anyway. The new commit/abort procedures will be used in the RelaX project (Reliable Distributed Applications Support on Unix), which carries on work done at GMD in the PROFEMO project on distributed transaction mechanisms.