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This is Ian Ozsvald's blog (@IanOzsvald), I'm an entrepreneurial geek, a Data Science/ML/NLP/AI consultant, author of O'Reilly's High Performance Python book, co-organiser of PyDataLondon, a Pythonista, co-founder of ShowMeDo and also a Londoner. Here's a little more about me.

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10 December 2014 - 13:31New Relic, uWSGI and “Cannot perform a data harvest for ‘‘ as there is no active session.”

This is more a note-to-self and maybe to another confused soul – if you’re using New Relic (it seems to be really rather nice for web app monitoring) with uWSGI, by default uWSGI runs without the GIL. This means no threads and this means New Relic won’t report anything which leads to a confusing first try.

Specifically read the Best Practices notes for uWSGI around “–enable-threads”. You have to add “–enable-threads” if you’re using New Relic’s Python agent, this is documented on their Python Agent Integration docs for uWSGI but for me the clue was in their log (by default in /tmp/newrelic-python-agent.log if you enable it in newrelic.ini) which showed:

(3717/NR-Harvest-Thread) newrelic.core.agent DEBUG 
 - Commencing harvest of all application data.
(3717/NR-Harvest-Thread) newrelic.core.application DEBUG 
 - Cannot perform a data harvest for '<appname>' as there is no active session.
(3717/NR-Harvest-Thread) newrelic.core.agent DEBUG 
 - Completed harvest of all application data in 0.00 seconds.

Once I’d added “–enable-threads” to uWSGI the logs looked a lot healthier, particularly:

(3292/NR-Harvest-Thread) newrelic.core.agent DEBUG 
 - Commencing harvest of all application data.
(3292/NR-Harvest-Thread) newrelic.core.application DEBUG 
 - Commencing data harvest of '<appname>'.
 ...
(3292/NR-Harvest-Thread) newrelic.core.application DEBUG 
 - Send profiling data for harvest of '<appname>'.
(3292/NR-Harvest-Thread) newrelic.core.application DEBUG 
 - Done sending data for harvest of '<appname>'.

Ian applies Data Science as an AI/Data Scientist for companies in ModelInsight, sign-up for Data Science tutorials in London. Historically Ian ran Mor Consulting. He also founded the image and text annotation API Annotate.io, co-authored SocialTies, programs Python, authored The Screencasting Handbook, lives in London and is a consumer of fine coffees.

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