Track-aligned extents (traxtents) utilize disk-specific knowledge to match access patterns to the strengths of modern disks. By allocating and accessing related data on disk track boundaries, a system can avoid most rotational latency and track crossing overheads. Avoiding these overheads can increase disk access efficiency by up to 50 % for mid-sized requests (100-500 KB). This paper describes traxtents, algorithms for detecting track boundaries, and some uses of traxtents in file systems and video servers. For large-file workloads, a version of FreeBSD's FFS implementation that exploits traxtents reduces application run times by up to 20 % compared to the original version. A video server using traxtent-based requests can support 56 % more concurrent streams at the same startup latency and buffer space. For LFS, 44 % lower overall write cost for track-sized segments can be achieved.

THOR is a persistent object store that provides a powerful programming model. THOR ensures that persistent objects are accessed only by calling their methods and it supports atomic transactions. The result is a system that allows applications to share objects safely across both space and time. The paper

This paper describes a new garbage collection scheme for large persistent object stores that makes efficient use of the disk and main memory. The heap is divided into partitions that are collected independently using information about inter-partition references. We present efficient techniques to maintain this information stably using auxiliary data structures in memory and the log. The result is a scheme that truly preserves the localized and scalable nature of partitioned collection. Remembering

Current commercial databases allow application programmers to trade off consistency for performance. However, existing definitions of weak consistency levels are either imprecise or they disallow efficient implementation techniques such as optimism. Ruling out these techniques is especially unfortunate because commercial databases support optimistic mechanisms. Furthermore, optimism is likely to be the implementation technique of choice in the geographically distributed and mobile systems of the future. This thesis presents the first implementation-independent specifications of existing ANSI isolation levels and a number of levels that are widely used in commercial systems, e.g., Cursor Stability, Snapshot Isolation. It also specifies a variety of guarantees for predicate-based operations in an implementation-independent manner. Two new levels are defined that provide useful consistency guarantees to application writers; one is the weakest level that ensures consistent reads, while the other captures some useful consistency properties provided by pessimistic implementations. We

This paper describes a newscheme for guaranteeing that transactions in a client/server system observe consistent state while they are running. The scheme is presented in conjunction with an optimistic concurrency control algorithm, but could also be used to prevent read-only transactions from conflicting with read/write transactions in a multi-version system. The scheme is lazy about the consistency it provides for running transactions and also in the way it generates the consistency information. The paper presents results of simulation experiments showing that the cost of the scheme is negligible. The scheme

Distributed persistent object systems provide a convenient environment for applications that need to manage complex long-lived data. Since Java has no persistence model built into it, the tremendous growth in the popularity of Java has generated a lot of interest in systems that add persistence to Java. This thesis presents the design, implementation and performance evaluation of a Java Persistent Store called JPS. JPS is an efficient distributed persistent Java system built on top of the Thor object-oriented database. JPS provides

Current client-server object database management systems employ either a page server or an object server architecture. Both of these architectures have their respective strengths, but they also have key drawbacks for important system and workload configurations. We propose a new hybrid server architecture which combines the best features of both page server and object server architectures while avoiding their problems. The new architecture incorporates new or adapted versions of data transfer, recovery, and cache consistency algorithms; in this paper we focus only on the data transfer and recovery issues. The data transfer mechanism allows the hybrid server to dynamically behave as both page and object server. The performance comparison of the hybrid server with object and page servers indicates that the performance of the hybrid server is more robust than the others.

SNAP is a novel high-performance snapshot system for object storage systems. The goal is to provide a snapshot service that is efficient enough to permit ”back-in-time” read-only activities to run against application-specified snapshots. Such activities are often impossible to run against rapidly evolving current state because of interference or because the required activity is determined in retrospect. A key innovation in SNAP is that it provides snapshots that are transactionally consistent, yet non-disruptive. Unlike earlier systems, we use novel in-memory data structures to ensure that frequent snapshots do not block applications from accessing the storage system, and do not cause unnecessary disk operations. SNAP takes a novel approach to dealing with snapshot meta-data using a new technique that supports both incremental meta-data creation and efficient meta-data reconstruction. We have implemented a SNAP prototype and analyzed its performance. Preliminary results show that providing snapshots for back-in-time activities has low impact on system performance even when snapshots are frequent. 1

This paper describes TimeLine, an efficient archive service for a distributed storage system. TimeLine allows users to take snapshots on demand. The archive is stored online so that it is easily accessible to users. It enables "time travel" in which a user runs a computation on an earlier system state. Archiving is challenging...

Applications of the future will need to support large numbers of clients and will require scalable storage systems that allow state to be shared reliably. Recent research in distributed file systems provides technology that increases the scalability of storage systems. But file systems only support sharing with weak consistency guarantees and can not support applications that require transactional consistency. The challenge is how to provide scalable storage systems that support transactional applications. We are developing technology for scalable transactional storage systems. Our approach combines scalable caching and coherence techniques developed in serverless file systems and DSM systems, with recovery techniques developed in traditional databases. This position paper describes the design rationale for split caching, a new scalable memory management technique for network-based transactional object storage systems, and fragment reconstruction, a new coherence protocol that supports...