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Zero-Downtime SQL Database Schema Evolution for...

Zero-Downtime SQL Database Schema Evolution for Continuous Deployment

MSc thesis defense presentation on QuantumDB.

Michael de Jong

August 26, 2015
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  1. Continuous Integration Write code Push to master Run test suite

    Package deliverable Deploy into production
  2. Write code Push to master Run test suite Package deliverable

    Deploy into production Continuous Delivery
  3. Write code Push to master Run test suite Package deliverable

    Deploy into production Continuous Deployment
  4. Continuous Deployment Faster release cycles Quick bug-fixes A/B testing ACID

    transactions Rigid schema Constraints for consistency SQL Databases
  5. How to deal with a SQL database when deploying a

    new version of a web service into production…
  6. How to deal with a SQL database when deploying a

    new version of a web service into production… … not so much
  7. 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
  8. API

  9. 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
  10. 82fba53 - CURRENT STATE 2ef5c1a 80bfa11 - FINAL STATE ADD

    COLUMN ADD FOREIGN KEY Defining changes
  11. 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
  12. 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
  13. #1 - DDL statements QuantumDB only applies DDL statements to

    tables which are not yet in use. Thus the client is never blocked by QuantumDB.
  14. #2 - Mixed-State Database clients can only access the tables

    in their chosen version of the database schema.
  15. 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
  16. Copying data is limited by disk I/O. We could actively

    throttle this based on some metric. Hardware limitations
  17. • QuantumDB, which supports complex schema changes on multiple tables.

    • Maintains referential integrity. • Can use up to two database schemas in parallel. Contributions
  18. • Do it in a non-destructive, non performance-degrading fashion. •

    Nemesis, which is able to benchmark various schema evolution scenarios. Contributions