Jun 4, 2024 · Query Processing includes translations of high-level Queries into low-level expressions that can be used at the physical level of the file system, query optimization, and actual execution of the query to get the actual result.

– Understand the factors affecting response time of a query • Query Processing Steps • Strategies for relational operations – Select (Point, Range), Join, set operations – Cost models • Query Optimization Module – Input: e.g. Query Trees / Graphs …

The query optimiser compares different strategies and chooses the strategy with the lowest cost. The optimiser must also limit the number of possibilities tested. This process is best suited to compiled queries.

Need scalability to larger-than-memory (on-disk) datasets and high performance at scale! Use an index that matches the SelectCondition I/O cost: Depends! For equality check, O(1) for hash index, and O(log(N)) for B+-tree index. ...

8. Query Processing Goals: Understand the basic concepts underlying the steps in query processing and optimization and estimating query processing cost; apply query optimization techniques; Contents: Overview Catalog Information for Cost Estimation Measures of Query Cost Selection Join Operations Other Operations Evaluation and Transformation ...

Query Processor of DBMSs 5 The component that executes a physical plan: A tree of operators that manipulate files and tuples to produce the output asked in a query. Operators implement core: 1. data access methods 2. query processing algorithms SELECT cid FROM Customer C, Order O, Product P WHERE C.cid = O.cid AND O.pid = P.pid

Algorithm A1 (linear search). Scan each file block and test all records to see whether they satisfy the selection condition. selection condition must be on search-key of index. A2 (clustering index, equality on key). Retrieve a single record that satisfies the corresponding equality condition .

In this chapter we discuss the techniques used internally by a DBMS to process, optimize, and execute high-level queries. A query expressed in a high-level query language such as SQL must first be scanned, parsed, and validated.

Introduction to the process of choosing a suitable execution strategy for processing a query. Translating SQL Queries into Relational Algebra ... Query block: the basic unit that can be translated into the algebraic operators and optimized.

Query Processing Sorting Algorithms Using B+Trees for Sorting • If the table that must be sorted already has a B+Tree index on the sort attribute(s), then we can use that to accelerate sorting. • Retrieve tuples in desired sort order by simply traversing the leaf pages of the tree. • Cases to consider: Clustered B+Tree Unclustered B+Tree