Fix for _PushStatus Stuck 'running' when Count is Off

[montymxb]

This is a proposed fix for #4315, where count computed for tracking outstanding pushes can differ from the actual # of devices that will be sent to.

During large operations this can occur where there is a significant time variation between the original computing of count and completion of the pushes. Also count can potentially provide an incorrect value on sharded dbs. With this in mind it makes more sense to track the batches instead. The # of batches is computed from the count that is set on _PushStatus, and even if the number of matched _Installation objects changes this does not. Given that, you can reliably track the batches instead of the count and still have an accurate running time.

This does not modify the existing behavior with count, so any dependence that anything or anyone may have on that factor is unchanged. The tracking for batches is achieved via an additional batches field on _PushStatus.

This adds some tests with a modified push adapter that either 'drops' or 'adds' installations during send ops to simulate count being inaccurate.

[codecov]

Codecov Report

Merging #4319 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4319      +/-   ##
==========================================
+ Coverage    92.5%   92.52%   +0.02%     
==========================================
  Files         118      118              
  Lines        8256     8256              
==========================================
+ Hits         7637     7639       +2     
+ Misses        619      617       -2

Impacted Files	Coverage Δ
src/Controllers/SchemaController.js	97.09% <ø> (ø)	⬆️
src/Push/PushQueue.js	100% <100%> (ø)	⬆️
src/StatusHandler.js	99.29% <100%> (+0.7%)	⬆️
src/RestWrite.js	93.57% <0%> (+0.18%)	⬆️

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[flovilmart]

I would completely remove the count as in the end, it’s useless to keep it as a count, perhaps use the number batch inside the count field instead. This way we don’t need to change the schema either.

[montymxb]

I originally used just count but was unsure if there was any referencing code on the dashboard or somewhere else that it might goof with. I can change that back if there's nothing like that.

[flovilmart]

Nope no references whatsoever. The scheduled state is not handled in the dashboard though:

[montymxb]

CI failed with the following:

• server has createLiveQueryServer

  • Failed: schema class name does not revalidate

• ParseLiveQueryServer can handle connect command

  • Failed: cannot perform operation: a background operation is currently running for collection parse._User

• Installations update android device token with duplicate device token

  • Expected 1 to equal 0.

Local looked fine so I'm rerunning to see if it clears.

[montymxb]

@flovilmart alright tests look good 👍

[flovilmart]

Looks great thanks!