This is documentation for the next version of Grafana Loki documentation. For the latest stable release, go to the latest version.

Log retention

Retention in Grafana Loki is achieved through the Compactor. By default the compactor.retention-enabled flag is not set, so the logs sent to Loki live forever.

Granular retention policies to apply retention at per tenant or per stream level are also supported by the Compactor.

Compactor

The Compactor is responsible for compaction of index files and applying log retention.

The Compactor loops to apply compaction and retention at every compactor.compaction-interval, or as soon as possible if running behind. Both compaction and retention are idempotent, which means once the action has been performed, if the action is performed multiple times, it has no further effect on logs after the first time it is performed. If the Compactor restarts, it continues from where it left off.

The Compactor’s algorithm to apply retention is as follows:

• For each day or table (one table per day with 24h index period):
  • Compact multiple index files in the table into per-tenant index files. Result of compaction is a single index file per tenant per day.
  • Traverse the per-tenant index. Use the tenant configuration to identify the chunks that need to be removed.
  • Remove the references to the matching chunks from the index and add the chunk references to a marker file on disk.
  • Upload the new modified index files.

Chunks are not deleted while applying the retention algorithm on the index. They are deleted asynchronously by a sweeper process and this delay can be configured by setting -compactor.retention-delete-delay. Marker files are used to keep track of the chunks pending for deletion.

Chunks cannot be deleted immediately for the following reasons:

• Index Gateway downloads a copy of the index files to serve queries and refreshes them at a regular interval. Having a delay allows the index gateways to pull the modified index file which would not contain any reference to the chunks marked for deletion. Without the delay, index files (that are stale) on the gateways could refer to already deleted chunks leading to query failures.

• It provides a short window of time in which to cancel chunk deletion in the case of a configuration mistake.

Marker files should be stored on a persistent disk to ensure that the chunks pending for deletion are processed even if the Compactor process restarts.

Retention Configuration

This Compactor configuration example activates retention.

compactor:
 working_directory: /data/retention
 compaction_interval: 10m
 retention_enabled: true
 retention_delete_delay: 2h
 retention_delete_worker_count: 150
 delete_request_store: gcs
schema_config:
 configs:
 - from: "2020-07-31"
 index:
 period: 24h
 prefix: index_
 object_store: gcs
 schema: v13
 store: tsdb
storage_config:
 tsdb_shipper:
 active_index_directory: /data/index
 cache_location: /data/index_cache
 gcs:
 bucket_name: loki

retention_enabled should be set to true. Without this, the Compactor will only compact tables.

delete_request_store should be set to configure the store for delete requests. This is required when retention is enabled.

working_directory is the directory where marked chunks and temporary tables will be saved.

compaction_interval dictates how often compaction and/or retention is applied. If the Compactor falls behind, compaction and/or retention occur as soon as possible.

retention_delete_delay is the delay after which the Compactor will delete marked chunks.

retention_delete_worker_count specifies the maximum quantity of goroutine workers instantiated to delete chunks.

Configuring the retention period

Retention period is configured within the limits_config configuration section.

There are two ways of setting retention policies:

• retention_period which is applied globally for all log streams.
• retention_stream which is only applied to log streams matching the selector.

This example configures global retention that applies to all tenants (unless overridden by configuring per-tenant overrides):

...
limits_config:
 retention_period: 744h
 retention_stream:
 - selector: '{namespace="dev"}'
 priority: 1
 period: 24h
 per_tenant_override_config: /etc/overrides.yaml
...

Per tenant retention can be defined by configuring runtime overrides. For example:

overrides:
 "29":
 retention_period: 168h
 retention_stream:
 - selector: '{namespace="prod"}'
 priority: 2
 period: 336h
 - selector: '{container="loki"}'
 priority: 1
 period: 72h
 "30":
 retention_stream:
 - selector: '{container="nginx", level="debug"}'
 priority: 1
 period: 24h

Retention period for a given stream is decided based on the first match in this list:

1. If multiple per-tenant retention_stream selectors match the stream, retention period with the highest priority is picked.
2. If multiple global retention_stream selectors match the stream, retention period with the highest priority is picked. This value is not considered if per-tenant retention_stream is set.
3. If a per-tenant retention_period is specified, it will be applied.
4. The global retention_period will be applied if none of the above match.
5. If no global retention_period is specified, the default value of 0s is used, which means logs are kept indefinitely.

Stream matching uses the same syntax as Prometheus label matching:

• =: Select labels that are exactly equal to the provided string.
• !=: Select labels that are not equal to the provided string.
• =~: Select labels that regex-match the provided string.
• !~: Select labels that do not regex-match the provided string.

The example configurations defined above will result in the following retention periods:

• For tenant 29:
  • Streams that have the namespace label prod will have a retention period of 336h (2 weeks), even if the container label is loki, since the priority of the prod rule is higher.
  • Streams that have the container label loki but are not in the namespace prod will have a 72h retention period.
  • For the rest of the streams in this tenant, per-tenant override retention_period value of 168h is applied.
• For tenant 30:
  • Streams that have the label nginx and level debug will have a retention period of 24h.
  • For the rest of the streams in this tenant the global retention period of 744h, since there is no override specified.
• All tenants except 29 and 30:
  • Streams that have the namespace label dev will have a retention period of 24h hours.
  • Streams except those with the namespace label dev will have the retention period of 744h.

Example Configuration

Example configuration with GCS with a 28 day retention:

schema_config:
 configs:
 - from: 2018-04-15
 store: tsdb
 object_store: gcs
 schema: v13
 index:
 prefix: loki_index_
 period: 24h

storage_config:
 tsdb_shipper:
 active_index_directory: /loki/index
 cache_location: /loki/index_cache
 gcs:
 bucket_name: GCS_BUCKET_NAME

limits_config:
 max_query_lookback: 672h # 28 days
 retention_period: 672h # 28 days

compactor:
 working_directory: /data/retention
 delete_request_store: gcs
 retention_enabled: true