Documentation Grafana Loki Manage Storage Log retention

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. If the Compactor restarts, it will continue 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.

yaml Copy

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):

yaml Copy

...
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:

yaml Copy

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 mutiple 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 744h (30days) retention is used.

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.

Table Manager (deprecated)

Retention through the Table Manager is achieved by relying on the object store TTL feature, and will work for both boltdb-shipper store and chunk/index stores.

In order to enable the retention support, the Table Manager needs to be configured to enable deletions and a retention period. Please refer to the table_manager section of the Loki configuration reference for all available options. Alternatively, the table-manager.retention-period and table-manager.retention-deletes-enabled command line flags can be used. The provided retention period needs to be a duration represented as a string that can be parsed using the Prometheus common model ParseDuration. Examples: 7d, 1w, 168h.

When using S3 or GCS, the bucket storing the chunks needs to have the expiry policy set correctly. For more details check S3’s documentation or GCS’s documentation.

The retention policy for Table manager can only be set globally. Per-tenant and per-stream retention policies along with support for deleting ingested logs using an API are only supported by Compactor retention.

Since a design goal of Loki is to make storing logs cheap, a volume-based deletion API is deprioritized. Until this feature is released, if you suddenly must delete ingested logs, you can delete old chunks in your object store. Note, however, that this only deletes the log content and keeps the label index intact; you will still be able to see related labels but will be unable to retrieve the deleted log content.

For further details on the Table Manager internals, refer to the Table Manager documentation.

Example Configuration

Example configuration with GCS with a 28 day retention:

yaml Copy

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