DbContextPool not decrementing active_dbcontexts metrics when overloaded

[gijs-hendrikx]

Bug description

I want to use the DbContext pool. Because I have a few places where it's up to the developer to properly dispose the DbContext I want to monitor pool usage and context disposal.

There are no metrics for the pool (e.g. rented out db contexts), so I tried monitoring the 'microsoft.entityframeworkcore.active_dbcontexts' metric. However I notice that this metric is not correct when used in combination with a pool.

I know that the metric includes the idle contexts in the pool as discussed in #35855 , but whenever the pool is exhausted and falls back to creating new contexts, those contexts are also not decremented from the metric after disposal, so you get an ever-incrementing metric.

A project to reproduce and show this error can be found here.

The project demonstrates the following:

• A pool of 20 db contexts
• Every 30 seconds: rent out 25 db contexts at once and dispose them all afterwards
• The active_dbcontexts metric keeps growing on each iteration (25, 30, 35, etc.). Even though my code disposes ALL db contexts and thus the active_dbcontexts metric should be equal to the pool size of 20.

This is a duplicate of #38306 but that issue was misunderstood and I can't re-open it or get in touch.

Your code

https://github.com/gijs-hendrikx/DbContextPool_Debugger

Stack traces

Verbose output

EF Core version

9.0.5

Database provider

No response

Target framework

.NET 10.0

Operating system

Windows 11

IDE

No response