C-Store: The Life of a Query

1. C-Store: The Life of a Query Jianlin Feng School of Software SUN YAT-SEN UNIVERSITY Mar 6, 2009

2. Main Components of a DBMS (1) • A typical DBMS has 5 main components • Client Communication Manager • Process Manager • Relational Query Processor • Transactional Storage Manager • Shared Components and Utilities

3. Main Components of a DBMS (2)

4. A Single-Query Transaction • At an airport, a gate agent clicks on a form to request the passenger list for a flight. • Example of Possible SQL statement SELECT name FROM Passenger Where flight = ‘510275’

5. Stage 1: Submit the SQL Statement • The Client: the personal computer at the airport gate • Calls an API to create a connection with the Client Communication Manager • The Client Communication Manager • Establish the security check of the Client • Set up states to remember the connection • And also remember the SQL statement • Forward the Client’s request deeper into the DBMS for processing.

6. Different Connection Arrangements • Two-tier or Client-server: • Client  Database Server • Via ODBC or JDBC • Three-tier • Client  Web Server  Database Server • Four-tier • Client  Web Server  App Server  Database Server

7. Stage 2: Assign a Thread of Computation • Upon receiving the SQL statement from the Client Communication Manager • The Process Manager first does Admission Control • The system should begin processing the query at once • Or defer to the time when the query can have enough resources for execution. • The Process Manager allocates a thread of control for a query • If the query should be executed at once.

8. Stage 3: Query Processing • The Relational Query Processor executes the query of the gate agent • Check if the agent is authorized to run the query • If authorized, compile the SQL query text into an internal query plan. • Query Parsing, Query Rewite / Optimization • Once compiled, the Plan Executor handles the query plan. • Invoke relation operators

9. Relational Operators (1) • Selection • File scan, B-Tree, Hash Index (Equality Selection) • Projection • Remove unwanted attributes • Eliminate any duplicates • Implement via sorting or hashing • Join • Nested Loops Join, Sort-Merge Join, Hash Join

10. Relational Operators (2) • Set • Union, Intersection, Difference, Cross product • Sorting or Hashing • Aggregation • SUM, MIN, MAX, COUNT, AVG • Data cube • Sorting or Hashing • Sorting • To get some good properties for speeding-up query

11. Stage 4: Fetch Data from Transactional Storage Manager • Plan Executor’s operators request data • Transactional Storage Manager manages calls for • All data access (READ) • All data manipulation (CREATE, UPDATE, DELETE) • And ensures ACID properties of transactions • Get locks from the Lock Manager • Interact with Log Manager for recovery preparation

12. Access Methods and Buffer Management • Access Methods • Algorithms and data structures for organizing and accessing data on disk. • Such as B-Tree, Hash, Bitmap Index • Buffer Management • Decides when and what data to transfer between disk and memory buffers.

13. Stage 5: Unwinding the Stack • After data access, access methods return control to the query executor’s operators. • Operators generate result tuples. • Result tuples are placed in a buffer for the Client Communication Manager • The Client Communication Manager ships the result tuples back to the Client. • At the end of the query, the transaction is completed. • Do clean-up jobs in each involved component.

14. References • Joseph M. Hellerstein, M. Stonebraker and J. Hamilton. Architecture of a Database System. Foundations and Trends in Databases 1(2). 2007. • Raghu Ramakrishnan and Johannes Gehrke. Database Management Systems. Second Edition. McGraw-Hill Science. 2000.