The SQL Server Database Engine can process Transact-SQL statements using two distinct processing modes: The following sections cover how SQL Server processes queries and optimizes query reuse through execution plan caching. the iterative plan is the binary program that when executes by the sql engine produces the result set.Įxecution Engine: Finally runs the query and display the required result.The SQL Server Database Engine processes queries on various data storage architectures such as local tables, partitioned tables, and tables distributed across multiple servers. The Row Source Generation is a software that receives a optimal execution plan from the optimizer and produces an iterative execution plan that is usable by the rest of the database. It is a process in which multiple query execution plan for satisfying a query are examined and most efficient query plan is satisfied for execution.ĭatabase catalog stores the execution plans and then optimizer passes the lowest cost plan for execution. This database never optimizes DDL unless it includes a DML component such as subquery that require optimization. Optimizer: During optimization stage, database must perform a hard parse atleast for one unique DML statement and perform optimization during this parse. Hard Parse includes following steps – Optimizer and Row source generation. It just passes directly to execution engine (refer detailed diagram). If there is a fresh query and its hash code does not exist in shared pool then that query has to pass through from the additional steps known as hard parsing otherwise if hash code exists then query does not passes through additional steps. So, this check determines existence of written hash code in shared pool if code exists in shared pool then database will not take additional steps for optimization and execution. Shared Pool check – Every query possess a hash code during its execution.Example: query contains a tablename which does not exist is checked by this check. Semantic check – determines whether the statement is meaningful or not. Here error of wrong spelling of FROM is given by this check. Syntax check – concludes SQL syntactic validity.Parser performs the following checks as (refer detailed diagram): Parser: During parse call, the database performs the following checks- Syntax check, Semantic check and Shared pool check, after converting the query into relational algebra. ISRO CS Syllabus for Scientist/Engineer Exam.ISRO CS Original Papers and Official Keys.GATE CS Original Papers and Official Keys.Full Stack Development with React & Node JS(Live).Preparation Package for Working Professional.Full Stack Development with React & Node JS (Live).Data Structure & Algorithm Classes (Live).
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