Quarterly Technical Report, January 2002
- New replication protocol: We continued to work on optimizing and evaluating
the replication architecture. We discovered and corrected several performance issues
with the engine itself and designed a significant latency optimization to Safe messages
in the Spread Toolkit that improved the performance of the replication system as a whole.
A complete replicated database solution for the PostgreSQL database was produced and
formed the basic version upon which we ran experiments.
We have completed a full set of experiments on
local and wide area networks. The experiments were conducted over a local cluster
in our lab, the CAIRN wide area network, and at the Emulab facility hosted by the
University of Utah. We were able to accurately emulate the physical topology of the
CAIRN network on the Emulab machines. The Emulab machines have processing and
disk IO resources comperable to those of our local cluster and we were able to get
excellent results for the replication engine that showed the efficiency of
the replication architecture and the practical capibility for wide area database
- Wackamole: We have developed and released a second version of Wackamole, a software
tool that allows N-Way Fail Over for IP Addresses in a cluster.
Wackamole now supports four platforms, Linux, FreeBSD, Solaris 8, and Mac OSX. This release
also focused on making Wackamole more robust and fixing deployment issues we received
from users. Based on email queries and downloads Wackamole has started to make
an impact as a different model for IP failover for clusters and to be used in practice.
- Archipelago: We have developed a third generation version of the Archipelago
system. This version completely reimplements the system with a modular design that
allows pluggable protocols and services such as routing, transport, and security.
This will allow us to use Archipelago as a flexible platform for experimentation
with specialized routing protocols and the cost-benefit framework. It also allows us
to use it in non-wireless, or hybrid wired-wireless environments.
The Archipelago system allows us to
investigate efficient ways to form an extended ad-hoc network of laptops,
handhelds, and other wireless capable devices, and bridge it to the Internet.
Archipelago constructs a multi-hop dynamic network using the wireless devices of participating users. The current system is fully operational, capable of
supporting up to about fifty participants using handhelds (Windows CE) and
desktops or laptops (Windows and Linux), and up to 10 hops in network diameter.
From Total Order to Database Replication
Technical Report CNDS-2001-6, November 2001.
and Ciprian Tutu.
This paper presents in detail an efficient and
provably correct algorithm for database replication over
partitionable networks. Our algorithm avoids the need for end-to-end
acknowledgments for each action while supporting network partitions and
merges and allowing dynamic instantiation of new replicas.
One round of end-to-end acknowledgments is required only upon a
membership change event such as a network partition. New actions may
be introduced to the system at any point, not only while in a
primary component. We show how performance can be further improved
for applications that allow relaxation of consistency requirements.
We provide experimental results that demonstrate the superiority of
Global Flow Control for Wide Area Overlay Networks: A Cost-Benefit Approach
Accepted to the Fifth IEEE Conference on Open Architectures and Network Programming June 2002.
This paper presents a flow control for multi-sender multi-group
multicast and unicast in wide area overlay networks.
The protocol is analytically grounded and achieves real world goals,
such as simplicity, fairness and minimal resource usage.
Flows are regulated based on the "opportunity" costs of
network resources used and the benefit provided by the flow.
In contrast to existing window-based flow
control schemes, we avoid end-to-end per sender or per group
feedback by looking only at
the state of the virtual links between participating nodes. This produces
control traffic proportional only to the number of overlay network
links and independent of the number of groups, senders or receivers.
We show the effectiveness of the resulting protocol
through simulations and validate the simulations with live Internet experiments.
On November 5, 2001 we released version 1.2.0 of Wackamole, an NxWay fail-over for
IP addresses in a cluster. Version 1.2.0 supports the Linux, FreeBSD, Solaris 8, and Mac OSX operating
systems. Wackmole is available at www.backhand.org/wackamole.
Plans for Next Quarter:
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