| 摘要 |
Methods, apparatus, and products are disclosed for the purposes of representing query plans for a query presented to a database in a manner generally referred to as an “EXPLAIN PLAN”, including query execution steps, query execution sequences, alternate query execution steps, and alternate query execution sequences for the query presented to the database management system, and for query plans, query execution steps, and query execution sequences for the execution of a parent query execution step. |
| 主权项 |
1. A database management system comprising:
a network interface, for receiving database queries from two or more client applications, the client applications operating on two or more user client computers, the system providing a least one connection into the system for each such client application; a group of two or more operational nodes for executing the queries as database operations, each operational node implemented as a logical collection of software components that execute on one or more physical machines; one or more client applications establish connections with the system and interact with the system in some query language; one or more operational nodes for storing data in tables, operating as storage nodes, and collectively referred to as a storage nodegroup; a Query Planner that analyzes queries submitted by one of the client applications and transforms the queries into a Chosen Query Plan that is to be executed by a Query Executor; the Chosen Query Plan comprising an ordered list of Query Execution Steps indicating an execution order, the execution order being a Query Execution Sequence, and including locations where individual steps of the Chosen Query Plan are to be executed; the Query Execution Sequence further identifying one or more dependencies amongst various steps in the Query Execution Steps, the dependencies such that at least one step must be executed before at least one other step; the Query Executor performing operations specified in the Query Execution Steps according to the Query Execution Sequence; in response to a command and an associated query, the Query Planner constructing Query Plans for the query; the software component on each operational node further inspecting and performing operations commanded by the Query Executor; the software component on each operational node independently generating a Subordinate Query Plan (SQP) that executes in response to the command that it receives from the Query Executor, at least two or more of the SQPs being dependent upon data stored in respective tables in the operational nodes, with the SQP for a first operational node being different from the SQP for a second operational node,
1. each operational node returning the SQP that it independently generates to the Query Planner; the Query Planner further returning information to one or more of the client applications as output in some human readable format, the output including
2. the Query Execution Steps of the chosen Query Plan;3. an identification of the operational nodes where individual steps of the chosen Query Plan are to be executed;the Query Execution Sequence of the chosen Query Plan;4. two or more of the SQPs generated by the operational nodes, including information indicating which of the steps and which of the operations within a step are to be executed before other steps, and information indicating dependencies between Query Execution Steps and operations within a Query Execution Step that comprise the two or more SQPs for corresponding operational nodes. |
