Max Kotliar 8e92cd3b2d lib/writeconcurrencylimiter: add some hints to unexpected EOF error message. (#8704) ...

### Describe Your Changes

Under heavy load, vmagent's wirte concurrency limiter

(2ab53acce4/lib/writeconcurrencylimiter/concurrencylimiter.go (L111))
queues incoming requests. If a client's timeout is shorter than the wait
time in the
queue, the client may close the connection before vmagent starts
processing it. When vmagent then tries to read the request body, it
encounters an ambiguous `unexpected EOF` error
(https://github.com/VictoriaMetrics/VictoriaMetrics/issues/8675).

This commit adds more context to such errors to help users diagnose and
resolve
the issue when it's related to vmagent's own load and queuing behavior.

Possible user actions include:
- Lowering `-insert.maxQueueDuration` below the client's timeout.
- Increasing the client-side timeout, if applicable.
- Scaling up vmagent (e.g., adding more CPU resources).
- Increasing `-maxConcurrentInserts` if CPU capacity allows.

Steps to reproduce:
https://gist.github.com/makasim/6984e20f57bfd944411f56a7ebe5b6bf

### Checklist

The following checks are **mandatory**:

- [x] My change adheres to [VictoriaMetrics contributing
guidelines](https://docs.victoriametrics.com/contributing/).

2025-04-13 11:22:12 +03:00

..

concurrencylimiter.go

lib/writeconcurrencylimiter: add some hints to unexpected EOF error message. (#8704)

2025-04-13 11:22:12 +03:00