10 research outputs found
Rethinking serializable multiversion concurrency control
Multi-versioned database systems have the potential to significantly increase
the amount of concurrency in transaction processing because they can avoid
read-write conflicts. Unfortunately, the increase in concurrency usually comes
at the cost of transaction serializability. If a database user requests full
serializability, modern multi-versioned systems significantly constrain
read-write concurrency among conflicting transactions and employ expensive
synchronization patterns in their design. In main-memory multi-core settings,
these additional constraints are so burdensome that multi-versioned systems are
often significantly outperformed by single-version systems.
We propose Bohm, a new concurrency control protocol for main-memory
multi-versioned database systems. Bohm guarantees serializable execution while
ensuring that reads never block writes. In addition, Bohm does not require
reads to perform any book-keeping whatsoever, thereby avoiding the overhead of
tracking reads via contended writes to shared memory. This leads to excellent
scalability and performance in multi-core settings. Bohm has all the above
characteristics without performing validation based concurrency control.
Instead, it is pessimistic, and is therefore not prone to excessive aborts in
the presence of contention. An experimental evaluation shows that Bohm performs
well in both high contention and low contention settings, and is able to
dramatically outperform state-of-the-art multi-versioned systems despite
maintaining the full set of serializability guarantees
Crux: Locality-Preserving Distributed Services
Distributed systems achieve scalability by distributing load across many
machines, but wide-area deployments can introduce worst-case response latencies
proportional to the network's diameter. Crux is a general framework to build
locality-preserving distributed systems, by transforming an existing scalable
distributed algorithm A into a new locality-preserving algorithm ALP, which
guarantees for any two clients u and v interacting via ALP that their
interactions exhibit worst-case response latencies proportional to the network
latency between u and v. Crux builds on compact-routing theory, but generalizes
these techniques beyond routing applications. Crux provides weak and strong
consistency flavors, and shows latency improvements for localized interactions
in both cases, specifically up to several orders of magnitude for
weakly-consistent Crux (from roughly 900ms to 1ms). We deployed on PlanetLab
locality-preserving versions of a Memcached distributed cache, a Bamboo
distributed hash table, and a Redis publish/subscribe. Our results indicate
that Crux is effective and applicable to a variety of existing distributed
algorithms.Comment: 11 figure
Design Principles for Scaling Multi-core OLTP Under High Contention
ABSTRACT Although significant recent progress has been made in improving the multi-core scalability of high throughput transactional database systems, modern systems still fail to achieve scalable throughput for workloads involving frequent access to highly contended data. Most of this inability to achieve high throughput is explained by the fundamental constraints involved in guaranteeing ACID -the addition of cores results in more concurrent transactions accessing the same contended data for which access must be serialized in order to guarantee isolation. Thus, linear scalability for contended workloads is impossible. However, there exist flaws in many modern architectures that exacerbate their poor scalability, and result in throughput that is much worse than fundamentally required by the workload. In this paper we identify two prevalent design principles that limit the multi-core scalability of many (but not all) transactional database systems on contended workloads: the multi-purpose nature of execution threads in these systems, and the lack of advanced planning of data access. We demonstrate the deleterious results of these design principles by implementing a prototype system, OR-THRUS, that is motivated by the principles of separation of database component functionality and advanced planning of transactions. We find that these two principles alone result in significantly improved scalability on high-contention workloads, and an order of magnitude increase in throughput for a non-trivial subset of these contended workloads