vectordotdev/vector · error

stream must exist

Error message

stream must exist

What it means

While building a Loki push request, events are grouped into streams keyed by their label set. The code inserts each new label set into stream_by_labels before mutating it, so a lookup miss at expect("stream must exist") is an internal bookkeeping bug: the code that should have inserted the stream did not. It is not caused by user event data shapes.

Solutions

1. Rebuild Vector from an unmodified source tree to rule out local patches to Loki event handling.
2. Check for abnormal label characters in events (use label drop/structured metadata settings) and sanitize event labels via VRL.
3. Upgrade Vector; if reproducible on stock builds, file a bug with the offending events.

// auto-restart on the rare internal panic
[Service]
Restart=on-failure

When it happens

Trigger: Building a Loki request where an event's computed labels key is not present in stream_by_labels even though the same pass inserted it — i.e., the labels value used for lookup differs from the one used for insertion (hashing/normalization mismatch between insert and get_mut).

Common situations: Effectively unreachable in stock Vector; would surface after code changes to label normalization or event partitioning in src/sinks/loki/event.rs, or with exotic label values exposing a hash/equality inconsistency.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• static
• a record with a next ID must have an event count
• a validated HTTP endpoint is a valid `http 1` URI
• building HTTP request failed unexpectedly
• Building request never fails.

AI-assisted analysis of vectordotdev/vector@bdb87aeaa4 (2026-09-16). Data as JSON: /api/errors/010a7aedd5b53548. Report an issue: GitHub.

Appendix: source

Thrown at src/sinks/loki/event.rs:121

                            })
                            .collect();
                        escaped.push(',');
                        escaped
                    })
                    .collect();
                if !res.stream_by_labels.contains_key(&labels) {
                    res.stream_by_labels.insert(
                        labels.clone(),
                        LokiStream {
                            stream: item.labels.into_iter().collect(),
                            values: Vec::new(),
                        },
                    );
                }
                let stream = res
                    .stream_by_labels
                    .get_mut(&labels)
                    .expect("stream must exist");
                stream.values.push(item.event);
                res
            });
        for (_k, stream) in result.stream_by_labels.iter_mut() {
            stream.values.sort_by_key(|e| e.timestamp);
        }
        result
    }
}

#[derive(Clone, Debug)]
pub struct LokiEvent {
    pub timestamp: i64,
    pub event: Bytes,
    pub structured_metadata: StructuredMetadata,
}

impl ByteSizeOf for LokiEvent {

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