93,349 research outputs found
From Cooperative Scans to Predictive Buffer Management
In analytical applications, database systems often need to sustain workloads
with multiple concurrent scans hitting the same table. The Cooperative Scans
(CScans) framework, which introduces an Active Buffer Manager (ABM) component
into the database architecture, has been the most effective and elaborate
response to this problem, and was initially developed in the X100 research
prototype. We now report on the the experiences of integrating Cooperative
Scans into its industrial-strength successor, the Vectorwise database product.
During this implementation we invented a simpler optimization of concurrent
scan buffer management, called Predictive Buffer Management (PBM). PBM is based
on the observation that in a workload with long-running scans, the buffer
manager has quite a bit of information on the workload in the immediate future,
such that an approximation of the ideal OPT algorithm becomes feasible. In the
evaluation on both synthetic benchmarks as well as a TPC-H throughput run we
compare the benefits of naive buffer management (LRU) versus CScans, PBM and
OPT; showing that PBM achieves benefits close to Cooperative Scans, while
incurring much lower architectural impact.Comment: VLDB201
Boosting Multi-Core Reachability Performance with Shared Hash Tables
This paper focuses on data structures for multi-core reachability, which is a
key component in model checking algorithms and other verification methods. A
cornerstone of an efficient solution is the storage of visited states. In
related work, static partitioning of the state space was combined with
thread-local storage and resulted in reasonable speedups, but left open whether
improvements are possible. In this paper, we present a scaling solution for
shared state storage which is based on a lockless hash table implementation.
The solution is specifically designed for the cache architecture of modern
CPUs. Because model checking algorithms impose loose requirements on the hash
table operations, their design can be streamlined substantially compared to
related work on lockless hash tables. Still, an implementation of the hash
table presented here has dozens of sensitive performance parameters (bucket
size, cache line size, data layout, probing sequence, etc.). We analyzed their
impact and compared the resulting speedups with related tools. Our
implementation outperforms two state-of-the-art multi-core model checkers (SPIN
and DiVinE) by a substantial margin, while placing fewer constraints on the
load balancing and search algorithms.Comment: preliminary repor
An Empirical Study of Speculative Concurrency in Ethereum Smart Contracts
We use historical data to estimate the potential benefit of speculative techniques for executing Ethereum smart contracts in parallel. We replay transaction traces of sampled blocks from the Ethereum blockchain over time, using a simple speculative execution engine. In this engine, miners attempt to execute all transactions in a block in parallel, rolling back those that cause data conflicts. Aborted transactions are then executed sequentially. Validators execute the same schedule as miners.
We find that our speculative technique yields estimated speed-ups starting at about 8-fold in 2016, declining to about 2-fold at the end of 2017, where speed-up is measured using either gas costs or instruction counts. We also observe that a small set of contracts are responsible for many data conflicts resulting from speculative concurrent execution
Distributed Management of Massive Data: an Efficient Fine-Grain Data Access Scheme
This paper addresses the problem of efficiently storing and accessing massive
data blocks in a large-scale distributed environment, while providing efficient
fine-grain access to data subsets. This issue is crucial in the context of
applications in the field of databases, data mining and multimedia. We propose
a data sharing service based on distributed, RAM-based storage of data, while
leveraging a DHT-based, natively parallel metadata management scheme. As
opposed to the most commonly used grid storage infrastructures that provide
mechanisms for explicit data localization and transfer, we provide a
transparent access model, where data are accessed through global identifiers.
Our proposal has been validated through a prototype implementation whose
preliminary evaluation provides promising results
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