Support "collection" tag in "mongodb.driver.commands" metric

[netme]

Currently, mongodb.driver.commands metric exposes the following tags:

• command
• cluster.id
• server.address
• status

https://github.com/micrometer-metrics/micrometer/blob/master/micrometer-core/src/main/java/io/micrometer/core/instrument/binder/mongodb/MongoMetricsCommandListener.java#L62

It would be great to make it more verbose and additionally expose MongoDB collection names.

[chrgue]

We were very happy when we found out there is a way to get such metrics.

But for services which are interacting with more than one collection the "collection" tag is mandatory to generate useful insights.

[netme]

Thanks, @chrgue for taking a look at this ticket

I have tried to mock a possible solution:

public class MongoMetricsCommandListener implements CommandListener {

    private final ConcurrentHashMap<Integer, String> collectionsCache;
    
    // ... 

    @Override
    public void commandStarted(final CommandStartedEvent event) {
        extractCollectionName(event)
                .ifPresent(it -> collectionsCache.put(event.getRequestId(), it));
    }

    @Override
    public void commandSucceeded(final CommandSucceededEvent event) {
        timeCommand(event, getCollectionNameOrUnknown(event), "SUCCESS", event.getElapsedTime(TimeUnit.NANOSECONDS));
    }

    @Override
    public void commandFailed(final CommandFailedEvent event) {
        timeCommand(event, getCollectionNameOrUnknown(event), "FAILED", event.getElapsedTime(TimeUnit.NANOSECONDS));
    }
    // ...
}

MongoDB driver does expose the collection name, however, it is only available in commandStarted. We can try to use some cache to get this data accessible in both commandSucceeded and commandFailed. What do you think about this approach?