Remove prefill logic from resource pool

[harshit-gangal]

Description

This PR modifies the resource pool by removing prefill logic and modifying benchmark tests.

Related Issue(s)

• RFC: Handle reserved/tainted connections better #9706

Checklist

• "Backport me!" label has been added if this change should be backported
• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[rsajwani]

I went through RFC as well but not able to find if this change is part of proposal #1, 2 or 3 .. Can you give me more detail why removing pre-fill logic

[harshit-gangal]

I went through RFC as well but not able to find if this change is part of proposal #1, 2 or 3 .. Can you give me more detail why removing pre-fill logic

It is a small refactor of the pool, and not directly related to RFC.

The prefill logic was not used in vitess deployment as the default value is 0 and the connection pool should be having lazy behaviour regarding opening connections to mysql.

[systay]

this seems unrelated. Why remove the tracing here?

[harshit-gangal]

The trace is already happening at one higher up level in connpool.Pool
Seems like an unnecessary trace.

	span.Annotate("capacity", p.Capacity())
	span.Annotate("in_use", p.InUse())
	span.Annotate("available", p.Available())
	span.Annotate("active", p.Active())

	if cp.timeout != 0 {
		var cancel context.CancelFunc
		ctx, cancel = context.WithTimeout(ctx, cp.timeout)
		defer cancel()
	}
	r, err := p.Get(ctx, nil)