The document discusses the journey of a database administrator from Oracle to PostgreSQL. It provides an overview of the speaker's background and experience with Oracle and PostgreSQL. It then compares some key differences between Oracle and PostgreSQL in areas like licensing, architecture and how each handles transactions and compliance with ACID properties. The document also outlines some advantages of PostgreSQL like its extensibility and some disadvantages like lack of parallelism. Overall, the speaker acknowledges Oracle's more advanced features but prefers using the free and open source PostgreSQL, working around limitations.

1. Journey from an
Oracle DBA
to a PostgreSQL DBA
11th June 2015
Disclaimer: The views expressed in this presentation are my own and does not represent the views of my company

2. Topics
1. About Me
2. Differences between Oracle & PostgreSQL
3. Personal experience with PostgreSQL

3. Topics
1. `whoami`
2. Difference between Oracle & PostgreSQL
3. Personal experience with PostgreSQL

4. `whoami`
● Ang Wei Shan
● Database Administrator
● 3 years in Oracle
● 1 year in SQL Server & DB2
● <2 months in PostgreSQL
● GMO GlobalSign

5. Topics
1. About Me
2. Differences between Oracle & PostgreSQL
3. Personal experience with PostgreSQL

6. Introduction
All comparisons are done using Oracle Database 11gR2 and PostgreSQL 9.3

7. ● Relational*
● ACID compliant
● Proprietary Licensing
● 35 years of active development
● “Owned” by a man who has an island
Oracle

8. ● Relational*
● ACID compliant
● Open-Source
● 25 years of active development
● Runs by core team of 6 from different
companies
PostgreSQL

9. Basic Concepts

10. ● Database is a set of files, located on disk
that stores data
● Instance is set of memory and processes
● Database <=== Instance
● A database may be accessed by 2 instances
at the same time.
Oracle

11. How does Oracle comply with ACID
● Atomicity
● Consistency
● Isolation
● Durability

12. Oracle - Undo and Redo Log
● Roll back transactions when a ROLLBACK statement is issued
● Recover the database
● Provide read consistency
● ORA-01555 Snapshot too old error
● Redo log consists of all the changes to the DB (Change Vector)
● All transactions will write to redo logs before committing
● Redo logs will contain Undo information
● Together, they can reconstruct all changes to the DB

13. ● Database cluster - A collection of databases
that is stored at a common file system
location ($PGDATA).
● 1 database cluster may contain 1 or more
databases
● Database cluster <=== Database
PostgreSQL

14. ● Atomicity
● Consistency
● Isolation
● Durability
How does PostgreSQL comply with ACID

15. ● Every transaction gets an incremental XID.
● Insert’s XID are called xmin (Update/Delete gets xmax)
● Every row that has been committed and xmin lesser than current
XID are visible to current TX
● Rows that are deleted are not removed but marked as deleted. The
rows that are deleted might still be required by other TX
● Will cause bloat-ness if not taken care off properly
● Vacuum will clean up unused rows (XID wraparound, ~4 bill rows)
● WAL are similar to Oracle’ redo logs
PostgreSQL - MVCC

16. Basic Architecture

17. Oracle

19. PostgreSQL

21. Topics
1. About Me
2. Differences between Oracle & PostgreSQL
3. Personal experience with PostgreSQL

22. ● Partial Index
● Python in database
● Foreign Data Wrapper
● Session level settings (isolation, replication)
● Easy to manage (l+, d+)
● User-defined data type
● Plenty of extensions to do more advance stuff (WAL-E,
Barman, pg_repack...)
PostgreSQL Yay! :)

23. ● No built-in parallelism
● No hints in DML query
● No advance security features
● No advance compression
● No default connection pooling
● Less mature replication technology
PostgreSQL Nay :(

24. Overall Thoughts

25. Require much more experienced people to
manage open-source than proprietary
technology. There are many different ways of
doing the same thing.

26. Oracle definitely beats PostgreSQL in terms of
technology…. But are you willing to pay USD
>45k per core license?

27. I would prefer to use it for free, find solutions
and work around the limitations. That is, after
all, the job of an engineer.

28. Thank you
weishan.ang@gmail.com
sg.linkedin.com/in/weishan
newbiedba.wordpress.com