Distributed query optimization method of equivalent expansion method based on relational algebra

Abstract

The invention discloses a distributed query optimization method of an equivalent expansion method based on relational algebra, and the method comprises the steps: sending a request, converting a language, constructing a query tree, optimizing fragments, decomposing the query tree, judging whether connection operation exists or not, calculating benefits and judging whether traversal is completed ornot. The method is scientific and reasonable in structure and safe and convenient to use. According to the method, the traditional SQl language is converted into the relational algebra expression byutilizing the consistency of the SQL language and the relational algebra, so that the efficiency of distributed query is indirectly improved, and the query tree is decomposed in the process of constructing the query tree, so the characteristic of data discrete distribution of a distributed system is better met, the data coupling between queries is reduced, the communication overhead is correspondingly reduced, the connection process is optimized through the MapReduce method, the communication overhead between stations in the connection process is greatly reduced, and the communication time iscorrespondingly shortened, so the query efficiency is improved.

Description

technical field [0001] The invention relates to the technical field of databases, in particular to a distributed query optimization method based on an equivalent expansion method of relational algebra. Background technique [0002] With the advent of the era of big data, data storage and query of large amounts of data has become a research hotspot for scholars; a distributed database system born out of a centralized database has also emerged as the times require. It is a combination of database management technology and network technology. product; in real life, a company can be geographically separated, with different subsidiaries set up in different regions, and the subsidiaries undertake their own business; however, the resources of different branches also need to be interacted and shared ; This is the embodiment of unity and autonomy; and the distributed database system also stores data in different nodes according to this concept, and interacts and accesses them through...

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Problems solved by technology

[0005] The present invention provides a distributed query optimization method based on the equivalent expansion method of relational algebra, which can effectively solve the problem that the traditional distributed query optimization proposed in the above background technology is based on the SQL language, and the optimization method is considered from the perspective of the global query initiated by the user. The method needs to consider the data distribution of each site associated with the query, and needs to judge from multiple angles to determine the optimization plan. At the same time, because the SQL language is more biased towards natural language, it is cumbersome to decompose into subqueries, and the actual query In the process, it often happens that multi-table join queries are required. The optimization algorithm based on direct join can easily lead to an excessive amount of transmitted data, thus causing excessive communication overhead.

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