Efficiency Of Query Execution Research Articles

Longshot: Indexing Growing Databases Using MPC and Differential Privacy

In this work, we propose Longshot, a novel design for secure outsourced database systems that supports ad-hoc queries through the use of secure multi-party computation and differential privacy. By combining these two techniques, we build and maintain data structures (i.e., synopses, indexes, and stores) that improve query execution efficiency while maintaining strong privacy and security guarantees. As new data records are uploaded by data owners, these data structures are continually updated by Longshot using novel algorithms that leverage bounded information leakage to minimize the use of expensive cryptographic protocols. Furthermore, Long-shot organizes the data structures as a hierarchical tree based on when the update occurred, allowing for update strategies that provide logarithmic error over time. Through this approach, Longshot introduces a tunable three-way trade-off between privacy, accuracy, and efficiency. Our experimental results confirm that our optimizations are not only asymptotic improvements but also observable in practice. In particular, we see a 5x efficiency improvement to update our data structures even when the number of updates is less than 200. Moreover, the data structures significantly improve query runtimes over time, about ~10 3 x faster compared to the baseline after 20 updates.

Full encryption

In this paper, we present a novel mechanism called Full Encryption (FE) in GaussDB. FE-in-GaussDB provides column-level encryption for sensitive data, and secures the asset from any malicious cloud administrator or information leakage attack. It ensures not only the security of operations on ciphertext data, but also the efficiency of query execution, by combining the advantages of cryptography algorithms (i.e. software mode) and Trusted Execution Environment (i.e. hardware mode). With this, FE-in-GaussDB supports full-scene query processing including the matching, the comparison and other rich computing functionalities. We demonstrate the prototype of FE-in-GaussDB and an experimental performance evaluation to prove its availability and effectiveness.

ACORE: A Query Optimization Approach for Spark SQL Based on Cost Model and Markov Prediction Model

Spark SQL is Spark’s module for working with structured data. However, there exist two problems that may impact its query execution efficiency: 1) Users may attempt to cache datasets used multiple times in a query to speed up the execution, but due to the predicate pushdown optimization and the overhead of writing cached data, the cached plan may turn out to have worse performance. 2) When using Spark dynamic resource allocation strategy, the release of idle executors would lead to the loss of cached data, introducing recalculation cost. To address these, we present an approach, named ACORE, which adaptively cache datasets and optionally release executors to optimize query execution of Spark SQL. The approach includes two models: a cost model and a Markov chain prediction model. The cost model is applied to estimate the execution cost for cached and un-cached plans, and decide which one to be the actual execution plan. The Markov prediction model is used to predict the changing trend of intervals between queries, guiding to optionally release executors to save cached data. We test the efficiency of our approach with data generated by TPC-H tool and the experimental results show that the execution performance can be improved by up to 51%.

A hybrid index for temporal big data

Temporal index provides an important way to accelerate query performance in temporal big data. However, the current temporal index cannot support the variety of queries very well, and it is hard to take account of the efficiency of query execution as well as the index construction and maintenance. In this paper, we propose a novel segmentation-based hybrid index B+-Tree, called SHB+- tree, for temporal big data. First, the temporal data in temporal table deposited is separated to fragments according to the time order. In each segment, the hybrid index is constructed by integrating the temporal index and the object index, and the temporal big data is shared by them. The performance of construction and maintenance is improved by employing the segmented storage strategy and bottom-up index construction approaches for every part of the hybrid index. The experimental results on benchmark data set verify the effectiveness and efficiency of the proposed method.

Применение графических ускорителей для обработки запросов над сжатыми данными в параллельных системах баз данных

This article talks about using graphics processors for query processing in parallel database systems. The goal is to evaluate query execution efficiency over compressed database without decompression on multicore GPUs which support CUDA technology. GPU’s memory size is significantly smaller than modern computer system’s RAM size. This fact affects database’s size can be loaded into GPU’s internal memory, thus computing potential of GPU can not be used efficiently. The new approach presented in this article allows query processing over compressed data on GPU. An emulator of parallel DBMS is developed based on this approach. The similar emulator for a CPU is designed. Results of computational experiments are presented and analysis of efficiency of the proposed approaches is performed.

Integrating Star and Snowflake Schemas in Data Warehouses

A fundamental issue encountered by the research community of data warehouses (DWs) is the modeling of data. In this paper, a new design is proposed, named the starnest schema, for the logical modeling of DWs. Using nested methodology, data semantics can be explicitly represented. Part of the design involves providing a translation mechanism from the star/snowflake schemas to a nested representation. The novel schema proposed in this paper is accomplished by converting the fact-dimension schema to a fact-nested dimension schema. The transformation of the denormalized dimension tables to nested dimension tables increases the efficiency of query execution by reducing the number of tuples accessed for query retrieval since dimensional attributes can be used directly in the Group-by clause. In order to facilitate the implementation of the proposed approach, specific algorithms are built based on the starnest schema.

Effective and efficient classification on a search-engine model

Traditional document classification frameworks, which apply the learned classifier to each document in a corpus one by one, are infeasible for extremely large document corpora, like the Web or large corporate intranets. We consider the classification problem on a corpus that has been processed primarily for the purpose of searching, and thus our access to documents is solely through the inverted index of a large scale search engine. Our main goal is to build the “best” short query that characterizes a document class using operators normally available within search engines. We show that surprisingly good classification accuracy can be achieved on average over multiple classes by queries with as few as 10 terms. As part of our study, we enhance some of the feature-selection techniques that are found in the literature by forcing the inclusion of terms that are negatively correlated with the target class and by making use of term correlations; we show that both of those techniques can offer significant advantages. Moreover, we show that optimizing the efficiency of query execution by careful selection of terms can further reduce the query costs. More precisely, we show that on our set-up the best 10-term query can achieve 93% of the accuracy of the best SVM classifier (14,000 terms), and if we are willing to tolerate a reduction to 89% of the best SVM, we can build a 10-term query that can be executed more than twice as fast as the best 10-term query.