  Transactional Memory (TM) is an approach to concurrency control that aims to
make writing parallel programs both effective and simple. The approach is
started in non-distributed multiprocessor systems, but is gaining popularity in
distributed systems to synchronize tasks at large scales. Efficiency and
scalability are often the key issues in TM research, so performance benchmarks
are an important part of it. However, while standard TM benchmarks like the
STAMP suite and STMBench7 are available and widely accepted, they do not
translate well into distributed systems. Hence, the set of benchmarks usable
with distributed TM systems is very limited, and must be padded with
microbenchmarks, whose simplicity and artificial nature often makes them
uninformative or misleading. Therefore, this paper introduces Helenos, a
realistic, complex, and comprehensive distributed TM benchmark based on the
problem of the Facebook inbox, an application of the Cassandra distributed
store.
