CS 257 Chapter – 15.9 Summary of Query Execution Database Systems: The Complete Book. Krishna Vellanki 124. Introduction. What is Query Processor? Group of components of a DBMS that converts a user queries and data-modification commands into a sequence of database operations
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CS 257Chapter – 15.9 Summary of Query ExecutionDatabase Systems: The Complete Book
What is Query Processor?
Number of reasons to sort a relation
Also denoted as B(R).
The choice of an algorithm for each operator is an essential
part of the process of transforming a logical query plan into
a physical query plan.
One-Pass Algorithms for Tuple-at-a-Time Operations: selection and projection
One-Pass Algorithms for Unary, fill-Relation Operations: Duplicate Elimination and Grouping
One-Pass Algorithms for Unary, fill-Relation Operations: Binary operations including Union, Intersection, Difference, Product and Join
To decrease the cost
Read too Late
Transaction T tries to read too late
Write too Late
Transaction T tries to write too late
T could perform a dirty read if it is reads X
A write is cancelled because of a write with a later timestamp, but the writer then aborts
Hashing is done if the data is too big to store in main memory buffers.
Steps to be followed for a Two passed Algorithm based on hashing