[scheduler] Support batch scheduling

[CaseyHillers]

Part of go/cocoon-scheduler

The current scheduler will always trigger runs. Before finishing the migration to the cocoon scheduler for flutter/flutter, it will need to support batch scheduling. This is because the DeviceLab doesn't have capacity to run on every commit.

• Create batch policy that will only trigger builds every 3 runs - [scheduler] Add batch scheduling logic cocoon#1685
• Create back filler cron job that schedules builds when capacity is available - [scheduler] Add backfilling cocoon#1776

[CaseyHillers]

There's some issue where backfilling doesn't apply. I'll take a look

[keyonghan]

There's some issue where backfilling doesn't apply. I'll take a look

Do you have the context what the issue is?

[CaseyHillers]

I left Mac_arm64_android integration_test_test on the Cocoon scheduler for debugging. It's getting back Backfilling 0 builds

The culprit code is likely in https://cs.opensource.google/flutter/cocoon/+/main:app_dart/lib/src/request_handlers/scheduler/batch_backfiller.dart;l=57-79

[keyonghan]

The culprit seems https://cs.opensource.google/flutter/cocoon/+/main:app_dart/lib/src/service/datastore.dart;l=145, it returns only 20 tasks which doesn't include those three tasks with a higher chance.

[keyonghan]

Issue fixed, and back filling is working as expected.

[github-actions]

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