How to think about performance

Selena DeckelmannPostgreSQL User Group Liaison

postgresql.org

End Point Corporation

Hubris

Case Study:How we are teaching people to think about

performance

PostgreSQL Portland Performance Practice

Project

Monthly meetings to talk about performance

http://pugs.postgresql.org/blog/92

Mark Wong

Meetings at Portland State University

Hardware donated by HP

Data center space from Command Prompt, Inc.

http://moourl.com/fsperf

Our data:

What do we teach?

BottlenecksBaselining

Constraints

Bottlenecks

sarmpstatiostatvmstatreadprofile

Baselining

• Application-specific.

• Filesystem performance.

• Start from defaults.

• Change one thing at a time.

• Use Science.

Constraints

• Hardware

• Operating system

• Time/Money

• Patience

We need your help.

• Go through our data.

• Pose new questions.

• Ask us about running tests.

How Postgres thinks about performance

Synchronized Scan

“Do you need to start at the beginning?”

• Have a sequential scan in progress?

• Piggy-back on that sequential scan.

• Version 8.3

HOT

“Don’t do something you don’t have to.”

• Heap Only Tuples (HOT)

• Have an UPDATE to a table that doesn’t affect an index?

• Don’t update the index.

• Version 8.3

Visibility Map

“Don’t do something you don’t have to.”

• Free Space Map shows space in table files that is available for reuse.

• Visibility Map is a bitmap that tells whether or not a tuple is visible to all transaction ids. If marked visible, don’t bother VACUUMing.

• Reduces VACUUM cost (less I/O)

• Version 8.4 (beta out now!)

Thanks!Postgres BoF 7:30pm

Camino Real@selenamarie (identi.ca/twitter)

selena@postgresql.org