Method for searching optimal execution plan in database query

Abstract

The invention relates to a method for searching an optimal execution plan in database query, comprising the following steps: execution plans which contain Cartesian product connection operation are not considered in the execution plan searching process (except that a query statement submitted by a user contains the Cartesian product connection operation); meanwhile, the connection relationship ofa relationship table in the statement is expressed in an image format; and finally, the optimal execution plan is searched in the image. The connection relationship of the statement expressed in the image format is as follows: points in the image represent the relationship in the query statement; two points are connected if the relationship corresponding to the two points in the image contains connection operation (including inner connection and outer connection); and the edge weight is the execution cost of the connection operation of two relationships. By using the structure, the optimal execution plan can be obtained in the concurrent execution environment.

Description

technical field [0001] The present invention relates to the field of databases, in particular to a search method for an optimal execution plan of a database execution plan in a concurrent execution environment during a SQL statement query process. Background technique [0002] During the query optimization process of the database, there are usually many possible strategies for a given SQL statement, especially a complex SQL statement. Generally speaking, if a query contains n relationships, there are (2(n-1))! / (n-1)! different connection sequences, when n=7, this number is 665280, and when n=10, this number is 17.6 billion. Query optimization is a process that can find out the less expensive execution plan from many strategies, but when the number of relationships involved in the sql statement is large (n>6), if the optimization engine traverses all execution plans one by one plan, will consume a lot of optimization time, and eventually lead to low query efficiency. ...

AI Technical Summary

Problems solved by technology

Query optimization is a process that can find out the less expensive execution plan from many strategies, but when the number of relationships involved in the sql statement is large (n>6), if the optimization engine traverses all execution plans one by one plan, will consume a lot of optimization time, and eventually lead to low query efficiency

In addition, with the emergence of a large number of multi-core servers, in order to improve the execution efficiency of statements, concurrent execution of statements will become the trend of statement execution in the future. In the past, when the query optimization engine selected the optimal execution plan, it did not take into account the premise of concurrent execution of statements. The optimal execution plan submitted by it cannot take full advantage of multi-core

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