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From Deng Xiaodong <xd.den...@gmail.com>
Subject Multiple Schedulers - "scheduler_lock"
Date Fri, 01 Mar 2019 15:25:10 GMT
Hi Max,

Following https://lists.apache.org/thread.html/0e21230e08f07ef6f8e3c59887e9005447d6932639d3ce16a103078f@%3Cdev.airflow.apache.org%3E
<https://lists.apache.org/thread.html/0e21230e08f07ef6f8e3c59887e9005447d6932639d3ce16a103078f@%3Cdev.airflow.apache.org%3E>,
I’m trying to prepare an AIP for supporting multiple-scheduler in Airflow (mainly for HA
and Higher scheduling performance).

Along the process of code checking, I found that there is one attribute of DagModel, “scheduler_lock”.
It’s not used at all in current implementation, but it was introduced long time back (2015)
to allow multiple schedulers to work together (https://github.com/apache/airflow/commit/2070bfc50b5aa038301519ef7c630f2fcb569620
<https://github.com/apache/airflow/commit/2070bfc50b5aa038301519ef7c630f2fcb569620>
).

Since you were the original author of it, it would be very helpful if you can kindly share
why the multiple-schedulers implementation was removed eventually, and what challenges/complexity
there were.
(You already shared a few valuable inputs in the earlier discussion https://lists.apache.org/thread.html/d37befd6f04dbdbfd2a2d41722352603bc2e2f97fb47bdc5ba454d0c@%3Cdev.airflow.apache.org%3E
<https://lists.apache.org/thread.html/d37befd6f04dbdbfd2a2d41722352603bc2e2f97fb47bdc5ba454d0c@%3Cdev.airflow.apache.org%3E>
, mainly relating to hiccups around concurrency, cross DAG prioritisation & load on DB.
Other than these, anything else you would like to advise?)

I will also dive into the git history further to understand it better.

Thanks.


XD
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