We describe an eficient server-based algorithm for garbage collecting object-oriented databases in a client/server environment. The algorithm is incremen-tal and runs concurrently with client transactions. Un-like previous algorithms, it does not hold any locks on data and does not require callbacks to clients. It is fault tolerant, but performs very little logging. The algorithm has been designed to be integrated into existing OODB systems, and therefore it works with standard implemen-tation techniques such as two-phase locking and write-ahead-logging. In addition, it supports client-server per-formance optimizations such as client caching and flexible management of client buffers. We describe an implemen-tation of the algorithm in the EXODUS storage manager and present results from an initial performance study. 1

The overall goal of the Emerald garbage collection scheme is to provide an efficient "on-thefly " garbage collection in a distributed object-based system that collects all garbage, and that is robust to partial failures. The first goal is to collect all garbage in the entire distributed system; we say that the collection is comprehensive in contrast to conservative collectors that only collect most garbage. Comprehensiveness is achieved by employing a system-wide mark-and-sweep collection based on concurrently running collectors, one on each node. The second goal of our collector is to be robust to partial failures. When facing node failures the collector will progress in the available parts of the system and, when necessary, wait for temporarily unavailable nodes to become available again. The scheme is being implemented on a network of VAXstations at DIKU. The full scheme employs two concurrent mark-and-sweep collectors on each node in the distributed system, one for comprehensivenes...

We describe an efficient server-based algorithm for garbage collecting object-oriented databases in a workstation/server environment. The algorithm is incremental and runs concurrently with client transactions, however, it does not hold any locks on data and does not require callbacks to clients. It is fault tolerant, but performs very little logging. The algorithm has been designed to be integrated into existing OODB systems, and therefore it works with standard implementation techniques such as two-phase locking and write-ahead-logging. In addition, it supports client-server performance optimizations such as client caching and flexible management of client buffers. We describe an implementation of the algorithm in the EXODUS storage manager and present results from an initial performance study of the implementation. These results demonstrate that the introduction of the garbage collector adds minimal overhead to client operations. 1 Introduction A primary strength of Object Oriented...

This paper addresses the problem of garbage collection in persistent object stores that are multilevel. The proposed approach is able to preserve referential integrity, while ensuring that security is not violated. In the paper, we first discuss some general principles that should underlie any approach to garbage collection in secure environments. Then, we present a secure garbage collection algorithm, based on the copying approach.