Documentation Grafana Loki Get started Labels Structured metadata

What is structured metadata

Selecting proper, low cardinality labels is critical to operating and querying Loki effectively. Some metadata, especially infrastructure related metadata, can be difficult to embed in log lines, and is too high cardinality to effectively store as indexed labels (and therefore reducing performance of the index).

Structured metadata is a way to attach metadata to logs without indexing them or including them in the log line content itself. Examples of useful metadata are kubernetes pod names, process ID’s, or any other label that is often used in queries but has high cardinality and is expensive to extract at query time.

Structured metadata can also be used to query commonly needed metadata from log lines without needing to apply a parser at query time. Large json blobs or a poorly written query using complex regex patterns, for example, come with a high performance cost. Examples of useful metadata include container_IDs or user IDs.

When to use structured metadata

You should only use structured metadata in the following situations:

• If you are ingesting data in OpenTelemetry format, using Grafana Alloy or an OpenTelemetry Collector. Structured metadata was designed to support native ingestion of OpenTelemetry data.
• If you have high cardinality metadata that should not be used as a label and does not exist in the log line. Some examples might include process_id or thread_id or Kubernetes pod names.
• If you are using Logs Drilldown to visualize and explore your Loki logs. You must set discover_log_levels and allow_structured_metadata to true in your Loki configuration.
• If you are a large-scale customer, who is ingesting more than 75TB of logs a month and are using Bloom filters (Experimental), starting in Loki 3.3 Bloom filters now utilize structured metadata.

Enable or disable structured metadata

You enable structured metadata in the Loki config.yaml file.

YAML Copy

limits_config:
    allow_structured_metadata: true
    volume_enabled: true
    retention_period: 672h # 28 days retention

You can disable Structured Metadata by setting allow_structured_metadata: false in the limits_config section or set the command line argument -validation.allow-structured-metadata=false. Note structured metadata is required to support ingesting OTLP data.

Attaching structured metadata to log lines

You have the option to attach structured metadata to log lines in the push payload along with each log line and the timestamp. For more information on how to push logs to Loki via the HTTP endpoint, refer to the HTTP API documentation.

Alternatively, you can use Grafana Alloy to extract and attach structured metadata to your log lines. See the Alloy stage.structured_metadata block for more information.

With Loki version 1.2.0, support for structured metadata has been added to the Logstash output plugin. For more information, see logstash.

Querying structured metadata

Structured metadata is extracted automatically for each returned log line and added to the labels returned for the query. You can use labels of structured metadata to filter log line using a label filter expression.

For example, if you have a label pod attached to some of your log lines as structured metadata, you can filter log lines using:

logql Copy

{job="example"} | pod="myservice-abc1234-56789"

Of course, you can filter by multiple labels of structured metadata at the same time:

logql Copy

{job="example"} | pod="myservice-abc1234-56789" | trace_id="0242ac120002"

Note that since structured metadata is extracted automatically to the results labels, some metric queries might return an error like maximum of series (50000) reached for a single query. You can use the Keep and Drop stages to filter out labels that you don’t need. For example:

logql Copy

count_over_time({job="example"} | trace_id="0242ac120002" | keep job  [5m])