PDTs - Useful Facts and Troubleshooting PDT Issues (Community)

View the original community article here

Last tested: Mar 20, 2017
 

The Basics
A PDT stands for Persistent Derived Table. It is a Looker-specific feature that allows users to create a table in the scratch schema of their database based on SQL they have written in Looker. Our docs on this are really good! PDT Documentation

Useful Facts

• The scratch schema needs to be configured in advance (see setup instructions).
• Use ${view_name.SQL_TABLE_NAME} to refer to a PDT in the SQL of a PDT (only replace view_name) - Docs
• Triggers are checked by default every 5 minutes when no triggered PDTs are building. This is configurable.
• A new PDT is created if you change the SQL in dev mode. See "why are there multiple copies of my PDT?" Dev mode PDTs have the persist_for: 24 hours property regardless of what persistence is set.

Troubleshooting Common PDT Issues

1. Make sure the SQL for the PDT runs by itself. Check this by copy and pasting the SQL from the view file into SQL Runner and see if it runs on the proper connection. 
2. Check the Admin > PDT panel for additional information on any PDTs which exist in production. Read more about the PDT Panel here.
3. Check the PDT Log in System Activity to see build and trigger events. This info is very robust.