1. OpenACS: Porting Oracle Applications to PostgreSQL Ben Adida ben@openforce.net

2. Using an Enterprise-Ready Open-Source RDBMS Ben Adida ben@openforce.net

3. Context Building a multi-user, networked application Open-Source hackers have ignored the RDBMS for too long! The Next Open-Source Challenge Can PostgreSQL replace Oracle?

4. Outline Open-Source and RDBMSs Oracle & PostgreSQL comparison –SQL support –Maintenance –Advanced Features Building a DB-independent App OpenACS

5. Data in Networked Apps Multiple users accessing data –Read & Write –Contention! Multiple means of access –Web server –Command line –Automated batch scripts

6. Data Abstraction Assurances made to application Understanding Failure: –Sometimes, you must fail –If you fail, admit it and fail gracefully Understanding Relevancy: –Sometimes certain data is irrelevant

7. ACID Abstraction for reliable data storage: Atomicity Consistency Isolation Durability

8. Atomicity All or nothing Much more than locking!

9. Consistency Invariants - Consistent States Complex Data Invariants –Audit Tables –Aggregate Checks Logic in the DB Logic triggered within transactional control

10. Isolation Partial work invisible to others Levels of Isolation –Dirty Reads –Read Committed –Read Repeatable –Serializable

11. Durability Once committed, a transaction is permanent -- no more rollbacks! Point-In-Time Recovery Impact on Backups

12. ACID in the DB locking, rollback in the application layer? Abstraction! Guarantees must be made no matter how data is accessed Isolation mandates implementation at low-level

13. ACID is not Enough! Naïve Implementation –single-threaded –global lock –full write to disk before commit. Get Fired Optimistic behavior

14. Does this Work? begin transaction; v_balance:= select balance from accounts where account_id=1; update accounts set balance= v_balance+20 where account_id=1; commit transaction;

15. This Does! begin transaction; v_balance:= select balance from accounts where account_id=1 for update; update accounts set balance= v_balance+20 where account_id=1; commit transaction;

16. Oracle - an Overview ACID-compliant Highly optimized for OLTP Highly configurable Very complex administration OPS: the Promised Land

17. PostgreSQL - an Overview ACId-compliant Highly optimized for OLTP Not so configurable Very simple administration Replication in the works

18. SQL support SQL92 - the “standard” No specifications for stored procedures or triggers! Ambiguities Oracle’isms –Connect By –Dates –SQL92 alternatives

19. SQL support Aggregates Joins, outer joins Subselects Views On-the-fly views

20. Stored Procedures Oracle PL/SQL, Java Triggers (statement and rowlevel) PostgreSQL PL/pgSQL, PL/Perl, PL/Tcl, PL/C Triggers (rowlevel only)

21. Transaction Engine Oracle Overwrite Rollback Segment Transaction Log (Redo Log) Row-Level Locking Optimistic PostgreSQL No-overwrite Versioning Transaction Log (as of v7.1) Row-Level Locking Optimistic

22. Backup & Recovery Oracle Logical Dump (not consistent!) Incremental dumps using physical backup Point-in-time recovery PostgreSQL Logical Dump (consistent) No incremental dumps No point-in-time recovery yet

23. Oracle Architecture Tablespace Rollback Segments

24. PostgreSQL Architecture …… Field: price Val: 120 Version # 1659 Field: price Val: 110 Version # 1660 Field: name Val: “Tim” Version # 1660 Field: price Val: 120 Version # 1661

25. Parallelism Oracle OPS Very few users However, a huge advantage in large installations PostgreSQL Asynchronous replication Synchronous in the works No complete solution yet

26. SQL Applications Interface via ODBC/JDBC, DBI, etc.. SQL statements –Many static, w/ bind variables Select * from users where user_id = :user_id –Some dynamic Select * from users where $date_predicate

27. Summary PostgreSQL can do 90% of what Oracle can do You probably need 70% of what Oracle can do PostgreSQL is ready for many enterprise systems.

28. OpenACS - History 1995 - AOLserver/Tcl/Illustra 1997 - AOLserver/Tcl/Oracle 1999 - AOLserver/Tcl/PostgreSQL 2001 - v4.x, multi-DB capable, modular

29. OpenACS 4.x Architecture PostgreSQL data model and stored procedures Queries stored in XML Templates AOLserver/Tcl logic

30. OpenACS Stack O/S RDBMS App Server Presentation OpenACS Custom Code All Free Software

31. OpenACS 4.x Features A common user table - collaboration Registration/Login/Permissions Discussion Forums Ecommerce Calendaring Education! (MIT Sloan)

32. OpenACS 4.x Demo

33. References http://postgresql.org http://openacs.org http://openacs.org/doc/openacs/? ?