Ioana Stanoi

Using broadcast primitives in replicated databases

We explore the use of different variants of broadcast protocols for managing replicated databases. Starting with the simplest broadcast primitive, the reliable broadcast protocol, we show how it can be used to ensure correct transaction execution. The protocol is simple, and has several advantages, including prevention of deadlocks. However, it requires a two-phase commitment protocol for ensuring correctness. We then develop a second protocol that uses causal broadcast and avoids the overhead of two-phase commit by exploiting the causal delivery properties of the broadcast primitives to implicitly collect the relevant information used in two-phase commit. Finally, we present a protocol that employs atomic broadcast and completely eliminates the need for acknowledgements during transaction commitment.

Data warehousing alternatives for mobile environments

With rapid advancement in technology, mobile devices are increasingly becomino the norm. These devices are charP acterized by their need to operate even when they are disconnected from the fixed non-mobile world. Since existing software technology is tuned to applications that operate in a fully connected world, this requirement of disconnected 6peration creates a need to adapt existing software technology to a partially disconnected world. Databases and filesystems have already been adapted to operate in a partially disconnected environment. However, little work has been done in the context of data warehousing in such an environment. We believe that there is a real need for adapting existing data warehousing technology for the mobile world. In this position paper, we show how techniques for hierarchical data warehouse management can be applied to data warehouses in a mobile environment. The techniques can be extended for other mobile applications. We present a variety of alternatives for systems in which some of the sources of data as well as the data warehouse itself is mobile.

Using broadcast primitives in replicated databases (abstract)

Recently there has been increasing interest in the development of broadcast protocols for disseminating information in distributed systems. Several protocols with varying properties have been proposed and implemented. One of the commonly cited applications is the management of replicated data. Most prior attempts concentrated on using atomic broadcast for file-like applications where single operations need to be executed on multiple copies of a file. We, on the other hand, explore the use of the simpler variants of broadcast protocols for managing replicated databases where the unit of activity is a transaction consisting of multiple operationa that need to be executed atomically as a unit. We assume a filly replicated database with tw~phaee locking. Reliable broadcod is a simple communication primitive that is easy to implement and guarantees eventual delivery. We make use of this guarantee to remove the need for explicit acknowledgement after every remote interaction. We adapt the read-one write-all protocol to a reliable broadcastbaaed system aa follows. A read operation is executed locally by acquiring a read lock. A write operation is executed by reliably broadcasting it to all database sites. On delivery, a site either acquires a write lock or the write operation is delayed until the lock can be granted. The transaction proceeds to execnte the next operation without waiting for afl write lrrcke to be granted, including at the initiator. When the initiating site decides to commit a transaction, it reliably broadcasts a commit requeet to all the sites. On delivery, a site checks if the transaction has any pending write operations. In this case, the acknowledgment for the commit is negative, otherwise positive. A transaction commits if all acknowledgements are positive, otherwise it aborts. This protocol avoids global deadlocks and read-only transactions are never aborted. We next examined the advantage of using causal broadcast for replicated databases. If we use a causal broadcast primitive instead of a reliable broadcast primitive in the above protocol, the modified protocol remains correct. The use of the different broadcast primitives offers some interest-

Modeling and Maintaining Multi-View Data Warehouses

Data warehouses are designed mostly as centralized systems, andt he majority of update maintenance algorithms are tailored for this specific model. Maintenance methods have been proposed either under the assumption of a single view data warehouse, a multi-view centralized model, or a multi-view distributed system with strict synchronization restrictions. We argue that extending this model to a multi-view distributedon e, is a practical generalization of the data warehouse system, andt he basis for a growing number of applications basedon the idea of cooperative views. In this paper we develop a general framework for modeling the maintenance of multi-views in a distributed, decentralized data warehouse, together with an efficient incremental algorithm for view maintenance. To our knowledge, there is no other proposal for a method that incorporates individually and asynchronously updates to different views that are related to each other through derivation dependencies.

View Derivation Graph with Edge Fitting for Adaptive Data Warehousing

In this paper we propose adaptive data warehouse maintenance, based on the optimistic partial replication of base source data that has already been used in deriving view tuples. Our method reduces local computation at the view as well as communication with the outside sources, and lowers the execution load on the base sources, which leads to a more up-to-date state of the data warehouse view.