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Documentation Grafana Enterprise Logs Manage Caching

Caching

Loki supports caching of index writes and lookups, chunks and query results to speed up query performance. This sections describes the recommended Memcached configuration to enable caching for chunks and query results. The index lookup cache is configured to be in-memory by default.

Before you begin

• It is recommended to deploy three, or in the case of the Helm chart two, dedicated Memcached clusters.
• As of 2023-02-01, the memcached:1.6.17-alpine version of the library is recommended.
• Consult the Loki ksonnet memcached deployment and the ksonnet memcached library.
• Index caching is not required for the TSDB index format.

Steps

To enable and configure Memcached:

1. Deploy each Memcached service with at least three replicas and configure each as follows:

   1. Chunk cache
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      --memory-limit=4096 --max-item-size=2m --conn-limit=1024

   2. Query result and index queries cache
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      --memory-limit=1024 --max-item-size=5m --conn-limit=1024

2. Configure Loki to use the cache.

   1. If the Helm chart is used

      Set memcached.chunk_cache.host to the Memcached address for the chunk cache, memcached.results_cache.host to the Memcached address for the query result cache, memcached.chunk_cache.enabled=true and memcached.results_cache.enabled=true.

      Ensure that the connection limit of Memcached is at least number_of_clients * max_idle_conns.

      The options host and service depend on the type of installation. For example, using the bitnami/memcached Helm Charts with the following commands, the service values are always memcached.

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      helm upgrade --install chunk-cache -n loki bitnami/memcached -f memcached-overrides-chunk.yaml
      helm upgrade --install results-cache -n loki bitnami/memcached -f memcached-overrides-results.yaml

      The current Helm Chart only supports the chunk and results cache.

      In this case, the Loki configuration would be

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      loki:
        memcached:
          chunk_cache:
            enabled: true
            host: chunk-cache-memcached.loki.svc
            service: memcached-client
            batch_size: 256
            parallelism: 10
          results_cache:
            enabled: true
            host: results-cache-memcached.loki.svc
            service: memcached-client
            default_validity: 12h

   2. If the Loki configuration is used, modify the following three sections in the Loki configuration file.

      1. Configure the chunk and index write cache
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         chunk_store_config:
           chunk_cache_config:
             memcached:
               batch_size: 256
               parallelism: 10
             memcached_client:
               host: <chunk cache memcached host>
               service: <port name of memcached service>

      2. Configure the query result cache
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         query_range:
           cache_results: true
           results_cache:
             cache:
               memcached_client:
                 consistent_hash: true
                 host: <memcached host>
                 service: <port name of memcached service>
                 max_idle_conns: 16
                 timeout: 500ms
                 update_interval: 1m

      3. Configure the index queries cache
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         storage_config:
           index_queries_cache_config:
             memcached:
               batch_size: 100
               parallelism: 100
             memcached_client:
               host: <memcached host>
               service: <port name of memcached service>
               consistent_hash: true