[AIRFLOW-2511] Fix improper failed session commit handling #4769
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@kaxil @bolkedebruin PTAL, thank you. |
Codecov Report
@@ Coverage Diff @@
## master #4769 +/- ##
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+ Coverage 74.44% 74.46% +0.01%
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Files 450 450
Lines 28973 28976 +3
==========================================
+ Hits 21570 21577 +7
+ Misses 7403 7399 -4
Continue to review full report at Codecov.
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ashb
reviewed
Feb 25, 2019
| @@ -2168,147 +2168,149 @@ def _process_backfill_task_instances(self, | |||
| # or leaf to root, as otherwise tasks might be | |||
| # determined deadlocked while they are actually | |||
| # waiting for their upstream to finish | |||
| @provide_session | |||
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Does this change also mean we open and close a connection for each TI? Does that have any impact on performance?
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Good point.
Not necessarily so, it just means that each TI gets its own session, which may or may not mapped to new connection as SQLAlchemy/Airflow does connection pooling. In fact, we use ti.refresh_from_db() a lot, where a new session object is created per call (
airflow/airflow/models/__init__.py
Line 932 in c50a851
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In general I think we should let SQLAlchemy do the pooling and close the sessions that we don't use anymore, instead of keeping them open and passing them around all the time.
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Personally I would prefer to have a create_session, since we commit the result on the last line anyway. If we do this properly, we shouldn't have to do refresh_from_db so often.
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I think SQLAlchemy does the pooling but is un-opinionated about how sessions are managed. The following access pattern is recommended per https://docs.sqlalchemy.org/en/latest/orm/session_basics.html#when-do-i-construct-a-session-when-do-i-commit-it-and-when-do-i-close-it, which is what Airflow follows:
Line 37 in c50a851
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Thanks for the reference link, no further concerns from my side.
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You've typod the Jira ticket in the commit - could you fix that please :) |
ashb
changed the title
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@ashb thanks for the review, replied your comment and fixed the typo [/facepalm]. |
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@ashb, a gentle ping, thanks. |
6 tasks
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(Sorry - inbox bankruptcy) |
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@fenglu-g this PR might have caused a failure on py3 on matter. Could you check? (I'm on mobile right now, so hard to say if it was this PR or another one.) Nevermind - it's Tornado 6.0.0 which was released 4 hours ago and breaks on our version of python. |
ashb
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Mar 19, 2019
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It looks as though this is still an issue post 1.10.3: |
andriisoldatenko
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Jul 26, 2019
wmorris75
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Jul 29, 2019
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Jira
Description
The bug is caused by improper clean up of failed session commit. This PR pulls out the per-task db manipulations within its own session through provide_session decorator. In the event a single commit fails, the decorate will ensure the session is properly flushed and closed.
Tests
This PR passes the tests.test_jobs unit test.
Commits
Documentation
Code Quality
flake8