444 research outputs found
Model Checking Paxos in Spin
We present a formal model of a distributed consensus algorithm in the
executable specification language Promela extended with a new type of guards,
called counting guards, needed to implement transitions that depend on majority
voting. Our formalization exploits abstractions that follow from reduction
theorems applied to the specific case-study. We apply the model checker Spin to
automatically validate finite instances of the model and to extract
preconditions on the size of quorums used in the election phases of the
protocol.Comment: In Proceedings GandALF 2014, arXiv:1408.556
MDCC: Multi-Data Center Consistency
Replicating data across multiple data centers not only allows moving the data
closer to the user and, thus, reduces latency for applications, but also
increases the availability in the event of a data center failure. Therefore, it
is not surprising that companies like Google, Yahoo, and Netflix already
replicate user data across geographically different regions.
However, replication across data centers is expensive. Inter-data center
network delays are in the hundreds of milliseconds and vary significantly.
Synchronous wide-area replication is therefore considered to be unfeasible with
strong consistency and current solutions either settle for asynchronous
replication which implies the risk of losing data in the event of failures,
restrict consistency to small partitions, or give up consistency entirely. With
MDCC (Multi-Data Center Consistency), we describe the first optimistic commit
protocol, that does not require a master or partitioning, and is strongly
consistent at a cost similar to eventually consistent protocols. MDCC can
commit transactions in a single round-trip across data centers in the normal
operational case. We further propose a new programming model which empowers the
application developer to handle longer and unpredictable latencies caused by
inter-data center communication. Our evaluation using the TPC-W benchmark with
MDCC deployed across 5 geographically diverse data centers shows that MDCC is
able to achieve throughput and latency similar to eventually consistent quorum
protocols and that MDCC is able to sustain a data center outage without a
significant impact on response times while guaranteeing strong consistency
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