Method and device for determining optimal query plan

Abstract

One or more embodiments of the invention provide a reference execution cost updating method for query step features. Basic information of the same or similar query steps has the same features, so that the corresponding relationship between the query step features and the reference execution cost is constructed by taking the features of the query steps as identifiers. The reference execution cost of the query step features are updated by obtaining execution result information after a database execution engine completes any query step, determining the features of the query step according to basic information of the query step, determining the actual execution cost of the query step information according to the execution result information, and then taking the actual execution cost as a reference execution cost corresponding to the query step features. Therefore, when the optimizer engine needs to evaluate the execution cost of a certain query step, the corresponding reference execution cost can be queried through the features of the query step.

Description

technical field [0001] One or more embodiments of this specification relate to the technical field of databases, and in particular to a method and device for determining an optimal query plan. Background technique [0002] The database generally includes a parser engine, an optimizer engine, and an executor engine. After the database receives a query request for a certain data, the parser engine parses it into a query plan and sends it to the optimizer engine. After optimization, the optimized query plan is sent to the execution engine, and the executor engine completes the query of the data according to the received query plan and obtains the query result. [0003] After receiving the query plan, the optimizer engine will decompose the query plan into query steps to determine whether each query step can be optimized. Specifically, when it is determined that a certain query step can be replaced by other query steps, by evaluating the query steps Execution cost, to determine...

AI Technical Summary

Problems solved by technology

[0004] In the prior art, the optimizer engine generally evaluates the execution cost information of each query step through the basic statistical information of the table, wherein the basic statistical information is stored in the system table of the database, including the number of tables, the rows of each table However, the basic statistical information needs to traverse each table for statistics. Therefore, in order not to waste query resources, the basic statistical information is generally updated when the database is idle or when there is a large amount of data changes. In some cases, although the actual content of the database has changed, the basic statistical information will not be updated in time, which will affect the accuracy of the optimization results

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