8,676 research outputs found
Stochastic Database Cracking: Towards Robust Adaptive Indexing in Main-Memory Column-Stores
Modern business applications and scientific databases call for inherently
dynamic data storage environments. Such environments are characterized by two
challenging features: (a) they have little idle system time to devote on
physical design; and (b) there is little, if any, a priori workload knowledge,
while the query and data workload keeps changing dynamically. In such
environments, traditional approaches to index building and maintenance cannot
apply. Database cracking has been proposed as a solution that allows on-the-fly
physical data reorganization, as a collateral effect of query processing.
Cracking aims to continuously and automatically adapt indexes to the workload
at hand, without human intervention. Indexes are built incrementally,
adaptively, and on demand. Nevertheless, as we show, existing adaptive indexing
methods fail to deliver workload-robustness; they perform much better with
random workloads than with others. This frailty derives from the inelasticity
with which these approaches interpret each query as a hint on how data should
be stored. Current cracking schemes blindly reorganize the data within each
query's range, even if that results into successive expensive operations with
minimal indexing benefit. In this paper, we introduce stochastic cracking, a
significantly more resilient approach to adaptive indexing. Stochastic cracking
also uses each query as a hint on how to reorganize data, but not blindly so;
it gains resilience and avoids performance bottlenecks by deliberately applying
certain arbitrary choices in its decision-making. Thereby, we bring adaptive
indexing forward to a mature formulation that confers the workload-robustness
previous approaches lacked. Our extensive experimental study verifies that
stochastic cracking maintains the desired properties of original database
cracking while at the same time it performs well with diverse realistic
workloads.Comment: VLDB201
What Makes a Place? Building Bespoke Place Dependent Object Detectors for Robotics
This paper is about enabling robots to improve their perceptual performance
through repeated use in their operating environment, creating local expert
detectors fitted to the places through which a robot moves. We leverage the
concept of 'experiences' in visual perception for robotics, accounting for bias
in the data a robot sees by fitting object detector models to a particular
place. The key question we seek to answer in this paper is simply: how do we
define a place? We build bespoke pedestrian detector models for autonomous
driving, highlighting the necessary trade off between generalisation and model
capacity as we vary the extent of the place we fit to. We demonstrate a
sizeable performance gain over a current state-of-the-art detector when using
computationally lightweight bespoke place-fitted detector models.Comment: IROS 201
Prototype of Fault Adaptive Embedded Software for Large-Scale Real-Time Systems
This paper describes a comprehensive prototype of large-scale fault adaptive
embedded software developed for the proposed Fermilab BTeV high energy physics
experiment. Lightweight self-optimizing agents embedded within Level 1 of the
prototype are responsible for proactive and reactive monitoring and mitigation
based on specified layers of competence. The agents are self-protecting,
detecting cascading failures using a distributed approach. Adaptive,
reconfigurable, and mobile objects for reliablility are designed to be
self-configuring to adapt automatically to dynamically changing environments.
These objects provide a self-healing layer with the ability to discover,
diagnose, and react to discontinuities in real-time processing. A generic
modeling environment was developed to facilitate design and implementation of
hardware resource specifications, application data flow, and failure mitigation
strategies. Level 1 of the planned BTeV trigger system alone will consist of
2500 DSPs, so the number of components and intractable fault scenarios involved
make it impossible to design an `expert system' that applies traditional
centralized mitigative strategies based on rules capturing every possible
system state. Instead, a distributed reactive approach is implemented using the
tools and methodologies developed by the Real-Time Embedded Systems group.Comment: 2nd Workshop on Engineering of Autonomic Systems (EASe), in the 12th
Annual IEEE International Conference and Workshop on the Engineering of
Computer Based Systems (ECBS), Washington, DC, April, 200
A fine-grain time-sharing Time Warp system
Although Parallel Discrete Event Simulation (PDES) platforms relying on the Time Warp (optimistic) synchronization
protocol already allow for exploiting parallelism, several techniques have been proposed to
further favor performance. Among them we can mention optimized approaches for state restore, as well as
techniques for load balancing or (dynamically) controlling the speculation degree, the latter being specifically
targeted at reducing the incidence of causality errors leading to waste of computation. However, in
state of the art Time Warp systems, events’ processing is not preemptable, which may prevent the possibility
to promptly react to the injection of higher priority (say lower timestamp) events. Delaying the processing
of these events may, in turn, give rise to higher incidence of incorrect speculation. In this article we present
the design and realization of a fine-grain time-sharing Time Warp system, to be run on multi-core Linux
machines, which makes systematic use of event preemption in order to dynamically reassign the CPU to
higher priority events/tasks. Our proposal is based on a truly dual mode execution, application vs platform,
which includes a timer-interrupt based support for bringing control back to platform mode for possible CPU
reassignment according to very fine grain periods. The latter facility is offered by an ad-hoc timer-interrupt
management module for Linux, which we release, together with the overall time-sharing support, within the
open source ROOT-Sim platform. An experimental assessment based on the classical PHOLD benchmark and
two real world models is presented, which shows how our proposal effectively leads to the reduction of the
incidence of causality errors, as compared to traditional Time Warp, especially when running with higher
degrees of parallelism
Attentional Encoder Network for Targeted Sentiment Classification
Targeted sentiment classification aims at determining the sentimental
tendency towards specific targets. Most of the previous approaches model
context and target words with RNN and attention. However, RNNs are difficult to
parallelize and truncated backpropagation through time brings difficulty in
remembering long-term patterns. To address this issue, this paper proposes an
Attentional Encoder Network (AEN) which eschews recurrence and employs
attention based encoders for the modeling between context and target. We raise
the label unreliability issue and introduce label smoothing regularization. We
also apply pre-trained BERT to this task and obtain new state-of-the-art
results. Experiments and analysis demonstrate the effectiveness and lightweight
of our model.Comment: 7 page
Towards lightweight convolutional neural networks for object detection
We propose model with larger spatial size of feature maps and evaluate it on
object detection task. With the goal to choose the best feature extraction
network for our model we compare several popular lightweight networks. After
that we conduct a set of experiments with channels reduction algorithms in
order to accelerate execution. Our vehicle detection models are accurate, fast
and therefore suit for embedded visual applications. With only 1.5 GFLOPs our
best model gives 93.39 AP on validation subset of challenging DETRAC dataset.
The smallest of our models is the first to achieve real-time inference speed on
CPU with reasonable accuracy drop to 91.43 AP.Comment: Submitted to the International Workshop on Traffic and Street
Surveillance for Safety and Security (IWT4S) in conjunction with the 14th
IEEE International Conference on Advanced Video and Signal based Surveillance
(AVSS 2017
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