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chore(loki): add query section

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Michele Cereda
2025-06-11 18:12:55 +02:00
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knowledge base/loki.md
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@@ -26,6 +26,7 @@ Designed to be cost-effective and easy to operate.
1. [Microservices mode](#microservices-mode)
1. [Object storage](#object-storage)
1. [Analytics](#analytics)
1. [Queries](#queries)
1. [Troubleshooting](#troubleshooting)
1. [Too many storage configs provided in the common config](#too-many-storage-configs-provided-in-the-common-config)
1. [Further readings](#further-readings)
@@ -702,6 +703,53 @@ analytics:
reporting_enabled: false
```
## Queries
Loki uses LogQL for queries.
Refer [Querying Logs with LogQL].
LogQL expressions consist of two main parts:
- A log stream selector.<br/>
This is in curly braces and defines which log streams to include or exclude.<br/>
It **must** define at least one stream to try and match, even if it does not exist.
- An optional pipeline of one or more expressions.<br/>
Those parse, filter, and format the log content from the stream.
```mermaid
graph LR
LSS(Log Stream selector)
LSF(Log Stream filter)
LLF(Log Line filter)
LLP(Log Line processor)
R(Results)
subgraph LogQL pipeline
direction LR
LSF --> LLF
LLF --> LLP
end
LSS --> LSF
LLP --> R
```
<details>
<summary>Examples</summary>
| Example | Summary |
| ---------------------------------------------- | ---------------------------------------------------------------------------------------------- |
| `{level="INFO"}` | Select lines with label `level` being `INFO` |
| `{service_name="prometheus", level="WARN"}` | Select lines with label `service_name` being `prometheus` **and** label `level` being `WARN` |
| `{service_name=~"app1\|app2"} \|= "someValue"` | Select lines with label `service_name` being `app1` or `app2` that contain `someValue` in them |
| `{level="DEBUG"} \| logfmt` | Parse lines using the `logfmt` format |
| `{level="DEBUG"} \| json \| UserID="nick"` | Filter on parsed fields |
| `count_over_time({app="loki"}[5m])` | Count lines over a window of 5m |
| `{job="mysql"} \|= "error" != "timeout"` | Include lines containing `error` but exclude the ones containing `timeout` |
</details>
## Troubleshooting
### Too many storage configs provided in the common config
@@ -867,4 +915,5 @@ storage_config:
[loki s3 storage: a guide for efficient log management]: https://last9.io/blog/loki-s3-storage-guide/
[loki-operator]: https://loki-operator.dev/
[opentelemetry / otlp]: https://loki-operator.dev/docs/open-telemetry.md/
[Querying Logs with LogQL]: https://deepwiki.com/grafana/loki-k6-handson/4-querying-logs-with-logql
[the quest for ha and dr in loki]: https://www.infracloud.io/blogs/high-availability-disaster-recovery-in-loki/