feat(tracing): track Cursor.toArray method for Mongo

[timofei-iatsenko]

Closes: #4495

Also added tests for mapReduce patching.

[timofei-iatsenko]

I have a question:

What happend if i span.startChild() and never finish it?

I'm trying to achieve something like this while tracing cursor:

-- find({query})
  -- toArray()
  -- count()
  -- other methods called on this cursor

To achieve this i'm creating a new span and passing it to instrumentCursor method, where creating child spans for every cursor method calls. But this parent 'cursorSpan' would be never finished explicitly because we don't know where it may happen.

I assuming if will not close it explicitly it should calculate time based on child spans. Am i right?

[AbhiPrasad]

I assuming if will not close it explicitly it should calculate time based on child spans. Am i right?

If the span is not explicitly closed, it will not be sent.

[AbhiPrasad]

I think this looks good as a initial start, we can come back and iterate as appropriate afterwards!

[timofei-iatsenko]

@AbhiPrasad do you have any ideas how to achieve what've described?

What would be if the parent span would be closed earlier than child spans?

Again i want to explicitly show in tracing than cursor is created with some params and then these methods are called on the cursor. I want this tracks to be coupled to each other.

Of course i can implement it differently and for each cursor method invocation just create a separate span and merge data spanContenxt from cursor creation and actual async method call.

[github-actions]

This pull request has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

[timofei-iatsenko]

@AbhiPrasad any news about that?

[AbhiPrasad]

Superceded by #6337