1. “Building Journaling Databases with PostgreSQL” Cybertec Geschwinde & Schoenig Hans-Juergen Schoenig (office@cybertec.at) www.postgresql.at www.cybertec.at

2. Common Problems * downtimes can be caused by: - hardware failures - network failures - software bugs - troubles caused by users * history and documentation “I don't remember what we have done “Who has changed this?” “What was the value before the change?”

3. What about the users? * data can be deleted accidentally by clicking on a wrong button * data is changed to something wrong => These problems cannot be solved by redudant hardware => restoring data can take a lot of time

4. Downtime vs. Uptime 99.9% uptime = 8 ½ hours downtime/year Assumption: * 100 people are affected by a problem * 1 hour downtime costs $50/person * average time for recovery 2 hours * 1 problem caused by a user per year => costs: $10.000 per year or 200 hours Reducing downtimes by 50% saves $5.000

5. The Idea Of Journaling * Every version of a record is stored * Every version of a record has: - a database wide unique id - a timestamp - a flag telling if a record is still valid or not - a transaction id to see which records have been changed within the same transaction - a user who has modified the record

6. Benefits of Journaling You can... * undo transactions * restore a snapshot of the database within minutes and without having to use your backup * monitor the changes made to your data * benchmark your employees * build a history of your data

7. Journaling And Performance Journaling databases are slower than “normal” databases due to overhead and a higher consumption of storage. In most cases this will NOT cause real performance problems.

8. A Case Study The Cybertec Intranet: Journaling helps us to: - keep track of the changes - increase the security of our data - see what has happened when - prevent errors 1 / 2

9. How does it work? 1 / 3 Historical + Current Data Functions And Rules Current Data View SELECT, INSERT, UPDATE, DELETE COPY, Triggers

10. How does it work? 2 / 3 CREATE TABLE t_mother ( globidint8, transidint4DEFAULT getxid(), transtimetimestamp without time zone DEFAULT now(), realtimetimestamp without time zone, statuschar DEFAULT 't', usernametext DEFAULT current_user() ); Historical + Current Data

11. How does it work? 3 / 3 Current Data View: - a recent version of the data is provided - the application can perform all common operations - the data is provided by a view Functions And Rules: - data structure is managed by rules - Functions are needed for managing serials, integrity, etc. Functions and Rules + Current Data View

12. Time Warps 3 / 3 Restoring Old Data: - old snapshots can be restored using a function called recovery - no data is lost during a Time Warp - recovery is based on functions Functions and Rules + Current Data View

13. Is it difficult? oreilly=# SELECT recovery('2002-05-06 23:49:26'); recovery ---------- t (1 row)

14. Any Questions? office@cybertec.at