pugs meetup presentation - 11062015
TRANSCRIPT
Journey from an Oracle DBA
to a PostgreSQL DBA11th June 2015
Disclaimer: The views expressed in this presentation are my own and does not represent the views of my company
Topics
1. About Me
2. Differences between Oracle & PostgreSQL
3. Personal experience with PostgreSQL
Topics
1. `whoami`
2. Difference between Oracle & PostgreSQL
3. Personal experience with PostgreSQL
`whoami`
● Ang Wei Shan● Database Administrator● 3 years in Oracle● 1 year in SQL Server & DB2● <2 months in PostgreSQL● GMO GlobalSign
Topics
1. About Me
2. Differences between Oracle & PostgreSQL
3. Personal experience with PostgreSQL
Introduction
All comparisons are done using Oracle Database 11gR2 and PostgreSQL 9.3
● Relational*● ACID compliant● Proprietary Licensing● 35 years of active development● “Owned” by a man who has an island
Oracle
● Relational*● ACID compliant● Open-Source● 25 years of active development● Runs by core team of 6 from different
companies
PostgreSQL
Basic Concepts
● 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
How does Oracle comply with ACID
● Atomicity
● Consistency
● Isolation
● Durability
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
● 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
● Atomicity
● Consistency
● Isolation
● Durability
How does PostgreSQL comply with ACID
● 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
Basic Architecture
Oracle
PostgreSQL
Topics
1. About Me
2. Differences between Oracle & PostgreSQL
3. Personal experience with PostgreSQL
● 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! :)
● 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 :(
Overall Thoughts
Require much more experienced people to manage open-source than proprietary technology. There are many different ways of doing the same thing.
Oracle definitely beats PostgreSQL in terms of technology…. But are you willing to pay USD >45k per core license?
I would prefer to use it for free, find solutions and work around the limitations. That is, after all, the job of an engineer.
