[AIRFLOW-1117] Change default min_file_process_interval

[mhousley]

The default min_file_process_interval=0 causes inordinately high CPU
consumption on small DAG sets.

Dear Airflow maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• My PR addresses the following Airflow JIRA issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-1117

Description

• Here are some details about my PR, including screenshots of any UI changes:
  • min_file_process_interval=0 causes the scheduler to rapidly loop over DAGs and consume inordinate processor time. Setting the default to 6 seconds slows the looping and avoids aligning with heartbeats.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:
  • This config change should not affect test coverage.

Commits

• My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

[codecov-io]

Codecov Report

Merging #2825 into master will decrease coverage by 2.82%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2825      +/-   ##
==========================================
- Coverage   76.67%   73.84%   -2.83%     
==========================================
  Files         199      159      -40     
  Lines       16186    12076    -4110     
==========================================
- Hits        12410     8918    -3492     
+ Misses       3776     3158     -618

Impacted Files	Coverage Δ
airflow/operators/email_operator.py	0% <0%> (-100%)	⬇️
airflow/hooks/pig_hook.py	0% <0%> (-100%)	⬇️
airflow/operators/slack_operator.py	0% <0%> (-97.37%)	⬇️
airflow/operators/s3_file_transform_operator.py	0% <0%> (-96.23%)	⬇️
airflow/operators/redshift_to_s3_operator.py	0% <0%> (-95.46%)	⬇️
airflow/hooks/mssql_hook.py	6.66% <0%> (-66.67%)	⬇️
airflow/hooks/hdfs_hook.py	32.5% <0%> (-60%)	⬇️
airflow/operators/hive_operator.py	41.02% <0%> (-45.52%)	⬇️
airflow/hooks/hive_hooks.py	39.52% <0%> (-33.9%)	⬇️
airflow/utils/helpers.py	53.44% <0%> (-30.93%)	⬇️
... and 196 more

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[gwax]

SGTM

[ron819]

This no longer needed after #3669

[dimberman]

Closing since this is a duplicate