Abstract. Recently a new generation of P2P systems, offering distributed hash table (DHT) functionality, have been proposed. These systems greatly improve the scalability and exact-match accuracy of P2P systems, but offer only the exact-match query facility. This paper outlines a research agenda for building complex query facilities on top of these DHT-based P2P systems. We describe the issues involved and outline our research plan and current status. 1

Berkeley DB is an Open Source embedded database system with a number of key advantages over comparable systems. It is simple to use, supports concurrent access by multiple users, and provides industrial-strength transaction support, including surviving system and disk crashes. This paper Berkeley DB describes the design and technical features of Berkeley DB, the distribution, and its license.

The dbm database library [1] introduced disk-based extensible hashing to UNIX. The library consists of functions to use a simple database consisting of key/value pairs. A number of work-alikes have been developed, offering additional features [5] and free source code [14,25]. Recently, a new package was developed that also offers improved performance [19]. None of these implementations, however, provide fault-tolerant behaviour. In many applications, a single high-level operation may cause many database items to be updated, created, or deleted. If the application crashes while processing the operation, the database could be left in an inconsistent state. Current versions of dbm do not handle this problem. Existing dbm implementations do not support concurrent access, even though the use of lightweight processes in a UNIX environment is growing. To address these deficiencies, tdbm was developed. Tdbm is a transaction processing database with a dbmlike interface. It provides nested atomic transactions, volatile and persistent databases, and support for very large objects and distributed operation. This paper describes the design and implementation of tdbm and examines its performance. 1.

An organization’s data is often its most valuable asset, but today’s file systems provide few facilities to ensure its safety. Databases, on the other hand, have long provided transactions. Transactions are useful because they provide atomicity, consistency, isolation, and durability (ACID). Many applications could make use of these semantics, but databases have a wide variety of non-standard interfaces. For example, applications like mail servers currently perform elaborate error handling to ensure atomicity and consistency, because it is easier than using a DBMS. A transaction-oriented programming model eliminates complex error-handling code, because failed operations can simply be aborted without side effects. We have designed a file system that exports ACID transactions to user-level applications, while preserving the ubiquitous and convenient POSIX interface. In our prototype ACID file system, called Amino, updated applications can protect arbitrary sequences of system calls within a transaction. Unmodified applications operate without any changes, but each system call is transaction protected. We also built a recoverable memory library with support for nested transactions to allow applications to keep their in-memory data structures consistent with the file system. Our performance evaluation shows that ACID semantics can be added to applications with acceptable overheads. When Amino adds atomicity, consistency, and isolation functionality to an application, it performs close to Ext3. Amino achieves durability up to 46% faster than Ext3, thanks to improved locality.

Today, software errors are the leading cause of outages in fault tolerant systems. System availability can be improved despite software errors by fast error detection and recovery techniques that minimize total downtime after an outage. This dissertation analyzes software errors in three commercial systems and describes the implementation and evaluation of several techniques for early error detection and fast recovery in a database management system (DBMS). The software error study examines errors reported by customers in three IBM systems programs: the MVS operating system and the IMS DBMS and DB2 DBMS. The study classifies errors by the type of coding mistake and the circumstances in the customer's environment that caused the error to arise. It observes a higher availability impact from addressing errors, such as uninitialized pointers, than software errors as a whole. It also details the frequencies and types of addressing errors and characterizes the damage they do. The error detec...

Optimistically replicated systems provide highly available data even when communication between data replicas is unreliable or unavailable. The high availability comes at the cost of allowing inconsistent accesses, since users can read and write old copies of data. Session guarantees [12] have been used to reduce such inconsistencies. They preserve most of the availability benefits of optimistic systems. We generalize session guarantees to apply to persistent as well as distributed entities. We implement these guarantees, called view consistency, on Ficus an optimistically replicated file system. Our implementation enforces consistency on a per-file basis and does not require changes to individual applications. View consistency is enforced by clients accessing the data and thus requires minimal changes to the replicated data servers. We show that view consistency allows access to available and high performing data replicas and can be implemented efficiently. Experimental results show that the consistency overhead for clients ranges from 1 % to 8 % of application runtime for the benchmarks studied in the prototype system. The benefits of the system are an improvement in access times due to better replica selection and improved consistency guarantees over a purely optimistic system. 1.

Storage management costs continue to increase despite the decrease in hardware costs. We propose a system to reduce storage maintenance costs by reducing the amount of data backed up and reclaiming disk space using various methods (e.g., transparently compress old files). Our system also provides a rich set of policies. This allows administrators and users to select the appropriate methods for reclaiming space. Our performance evaluation shows that the overheads under normal use are negligible. We report space savings on modern systems ranging from 25% to 76%, which result in extending storage lifetimes by 72%.

Email is one of the most important of the Internet services. As a very large, fast growing, Internet Service Provider, EarthLink requires a robust and powerful email architecture that will support rapid expansion. This paper describes such an architecture, its motivations, its future, and the di culties in implementing a service on this scale. 1

this paper, we present a description of NileFT and the status of its implementation.

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