conncache - skip caching errors

[egor-ryashin]

Depends on this #5218

[begelundmuller]

Seems like this just skips caching errors entirely? Having a TTL as described in the issue might be preferable: #5076

Also, there are CI failures.

[egor-ryashin]

I guess, you propose something like this:

	go func() {
		for true {
			time.Sleep(5 * time.Second)
			go func() {
				c.mu.Lock()
				defer c.mu.Unlock()
				for k, v := range c.entries {
					if v.err != nil && time.Now().Sub(v.previousErrTime) > 100*time.Second {
						c.beginClose(k, v)
					}
				}
			}()
		}
	}()

[egor-ryashin]

CI fixed, need a design review.

[begelundmuller]

1. It looks like this is not set anywhere?
2. Consider calling it ErrorTTL instead since it's not a timeout the same way that OpenTimeout and CloseTimeout are

[egor-ryashin]

Done.

[begelundmuller]

This is missing cancellation from Close. Instead of having a background loop (which adds concurrency complexity), how about just checking the TTL when accessing a cached error in Acquire? That should still ensure correctness, and cleanup for connections that are not acquired again anyway happens automatically by the LRU cache

[egor-ryashin]

Done.

[egor-ryashin]

Tests passed.