Zero-Downtime SQL Database Schema Evolution for Continuous Deployment

MSc thesis defense presentation on QuantumDB.

Transcript

1. Zero-Downtime SQL Database Schema Evolution for Continuous Deployment Michael de Jong
2. Deployment Continuous
3. Write code Push to master Run test suite Package deliverable Deploy into production
4. Write code Push to master Run test suite Package deliverable Deploy into production
5. Write code Push to master Run test suite Package deliverable Deploy into production
6. Write code Push to master Run test suite Package deliverable Deploy into production
7. Write code Push to master Run test suite Package deliverable Deploy into production
8. Write code Push to master Run test suite Package deliverable Deploy into production
9. Continuous Integration Write code Push to master Run test suite Package deliverable Deploy into production
10. Write code Push to master Run test suite Package deliverable Deploy into production Continuous Delivery
11. Write code Push to master Run test suite Package deliverable Deploy into production Continuous Deployment
12. SO WHAT’S THE Problem?
13. SQL Databases
14. Continuous Deployment Faster release cycles Quick bug-fixes A/B testing ACID transactions Rigid schema Constraints for consistency SQL Databases
15. Continuous Deployment Continuous change VS. Change? No thank you… SQL Databases
16. Deploying a new version of a web service into production is well understood.
17. How to deal with a SQL database when deploying a new version of a web service into production…
18. How to deal with a SQL database when deploying a new version of a web service into production… … not so much
19. “I deploying database schema changes into production!” — said no software engineer ever
20. Reason 1: DDL statements
21. Nemesis:
22. MySQL 5.5 MySQL 5.6 PostgreSQL 9.3 PostgreSQL 9.4 S1 Read-only Non-Blocking Blocking Blocking S2 Read-only Non-Blocking Non-Blocking Non-Blocking S3 Read-only Non-Blocking Non-Blocking Non-Blocking S4 Read-only Non-Blocking Non-Blocking Non-Blocking S5 Read-only Non-Blocking Non-Blocking Non-Blocking S6 Read-only Non-Blocking Non-Blocking Non-Blocking S7 N/A N/A Non-Blocking Non-Blocking S8 N/A N/A Non-Blocking Non-Blocking S9 N/A N/A Blocking Blocking S10 Read-only Read-only Non-Blocking Non-Blocking S11 Read-only Read-only Blocking Blocking S12 Non-Blocking Non-Blocking Non-Blocking Non-Blocking S13 Non-Blocking Non-Blocking Non-Blocking Non-Blocking S14 Read-only Read-only Blocking Blocking S15 Read-only Read-only Blocking Blocking S16 Read-only Non-Blocking Non-Blocking Non-Blocking S17 N/A N/A Non-Blocking Blocking S18 Blocking Non-Blocking Non-Blocking Non-Blocking S19 Non-Blocking Non-Blocking Non-Blocking Non-Blocking
23. Reason 2: Mixed-State
24. API
25. API API NEW
26. Reason 3: Referential Integrity
27. QuantumDB’s Approach
28. Imagine if you will… movies rentals customers
29. changelog.addChangeSet(“Add referral column to customers table”, addColumn(“customers”, “referred_by”, integer()), addForeignKey(“customers”, “referred_by”) .named(“customer_referred_by_fk”) .onDelete(NO_ACTION) .referencing(“customers”, “id”)); Defining changes
30. 82fba53 - CURRENT STATE 2ef5c1a 80bfa11 - FINAL STATE ADD COLUMN ADD FOREIGN KEY Defining changes
31. movies rentals customers Evolving the database schema
32. movies rentals customers customers* Evolving the database schema
33. movies rentals rentals* customers customers* Evolving the database schema
34. movies rentals* customers* rentals customers Evolving the database schema
35. movies rentals* customers* rentals customers Evolving the database schema
36. movies rentals* customers* rentals customers Evolving the database schema
37. movies customers* rentals customers rentals* Evolving the database schema
38. Accessing the database movies rentals* customers* rentals customers 82fba53
39. 80bfa11 82fba53 movies rentals* customers* rentals customers Accessing the database
40. Accessing the database Application Driver
41. Application Wrapper Driver Accessing the database
42. Connection connection = DriverManager.getConnection( “jdbc:postgresql://localhost:5432/database”, “username”, “password”); Connection connection = DriverManager.getConnection( “jdbc:quantumdb:postgresql://localhost:5432/database?version=80bfa11”, “username”, “password”); Accessing the database
43. SELECT * FROM rentals WHERE customer_id = 2372 AND return_date < NOW() AND returned = false; SELECT * FROM rentals* WHERE customer_id = 2372 AND return_date < NOW() AND returned = false; Accessing the database
44. movies customers* rentals customers rentals* Dropping a database schema
45. movies rentals* customers* rentals customers Dropping a database schema
46. movies rentals* customers* Dropping a database schema
47. 80bfa11 movies rentals* customers* Dropping a database schema
48. Demo-Time!
61. LET’S Evaluate
62. #1 - DDL statements QuantumDB only applies DDL statements to tables which are not yet in use. Thus the client is never blocked by QuantumDB.
63. #2 - Mixed-State Database clients can only access the tables in their chosen version of the database schema.
64. #3 - Referential Integrity Foreign key constraints are always adhered to, and mirrored when needed.
65. Too good to be true?
66. Supported databases
67. SUPPORTED ADD COLUMN ALTER COLUMN DROP COLUMN CREATE TABLE COPY TABLE RENAME TABLE DROP TABLE ADD FOREIGN KEY DROP FOREIGN KEY CREATE INDEX DROP INDEX NOT (YET) SUPPORTED DML STATEMENTS ADD CHECK CONSTRAINT DROP CHECK CONSTRAINT DECOMPOSE TABLE * JOIN TABLE * MERGE TABLE * PARTITION TABLE * * Update Rewriting and Integrity Constraint Maintenance in a Schema Evolution Support System: PRISM++ Supported operations
68. Copying data is limited by disk I/O. We could actively throttle this based on some metric. Hardware limitations
69. • QuantumDB, which supports complex schema changes on multiple tables. • Maintains referential integrity. • Can use up to two database schemas in parallel. Contributions
70. • Do it in a non-destructive, non performance-degrading fashion. • Nemesis, which is able to benchmark various schema evolution scenarios. Contributions
71. QuantumDB quantumdb.io - @java_devver