Distributed Garbage Collection by Timeouts and Backward Inquiry

We present a practical and e cient garbage collection mechanism for large scale distributed systems The mechanism collects all garbage including distributed cyclic garbage without global synchronization or back ward links The primary method used for local and remote garbage collection is timeouts each object has a time to live and clients which have a link to an ob ject must refresh the target object within the time to live to guarantee that the link will remain valid For cyclic garbage collection objects suspected to be garbage are detected by last referenceable timestamp propaga tion and cyclic garbage is reclaimed by backward inquiry back tracing Since without additional overhead the information about backward references can be obtained during the refreshing process and since messages neces sary for cyclic garbage collection are bundled with the messages used for the refreshing communication com putation and storage overhead is minimized This mech anism has been implemented and evaluated on Prospero directory service and the performance results show that it works well for large scale distributed systems