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druid/docs/content/querying/lookups.md

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Lookups

Lookups are an experimental feature.

Lookups are a concept in Druid where dimension values are (optionally) replaced with new values, allowing join-like functionality. Applying lookups in Druid is similar to joining a dimension table in a data warehouse. See dimension specs for more information. For the purpose of these documents, a "key" refers to a dimension value to match, and a "value" refers to its replacement. So if you wanted to map appid-12345 to Super Mega Awesome App then the key would be appid-12345 and the value would be Super Mega Awesome App.

It is worth noting that lookups support not just use cases where keys map one-to-one to unique values, such as country code and country name, but also support use cases where multiple IDs map to the same value, e.g. multiple app-ids mapping to a single account manager. When lookups are one-to-one, Druid is able to apply additional optimizations at query time; see Query execution below for more details.

Lookups do not have history. They always use the current data. This means that if the chief account manager for a particular app-id changes, and you issue a query with a lookup to store the app-id to account manager relationship, it will return the current account manager for that app-id REGARDLESS of the time range over which you query.

If you require data time range sensitive lookups, such a use case is not currently supported dynamically at query time, and such data belongs in the raw denormalized data for use in Druid.

Very small lookups (count of keys on the order of a few dozen to a few hundred) can be passed at query time as a "map" lookup as per dimension specs.

Other lookup types are available as extensions, including:

Query Execution

When executing an aggregation query involving lookups, Druid can decide to apply lookups either while scanning and aggregating rows, or to apply them after aggregation is complete. It is more efficient to apply lookups after aggregation is complete, so Druid will do this if it can. Druid decides this by checking if the lookup is marked as "injective" or not. In general, you should set this property for any lookup that is naturally one-to-one, to allow Druid to run your queries as fast as possible.

Injective lookups should include all possible keys that may show up in your dataset, and should also map all keys to unique values. This matters because non-injective lookups may map different keys to the same value, which must be accounted for during aggregation, lest query results contain two result values that should have been aggregated into one.

This lookup is injective (assuming it contains all possible keys from your data):

1 -> Foo
2 -> Bar
3 -> Billy

But this one is not, since both "2" and "3" map to the same key:

1 -> Foo
2 -> Bar
3 -> Bar

To tell Druid that your lookup is injective, you must specify "injective" : true in the lookup configuration. Druid will not detect this automatically.

Dynamic Configuration

Dynamic lookup configuration is an experimental feature. Static configuration is no longer supported.
The following documents the behavior of the cluster-wide config which is accessible through the coordinator. The configuration is propagated through the concept of "tier" of servers. A "tier" is defined as a group of services which should receive a set of lookups. For example, you might have all historicals be part of `__default`, and Peons be part of individual tiers for the datasources they are tasked with. The tiers for lookups are completely independent of historical tiers.

These configs are accessed using JSON through the following URI template

http://<COORDINATOR_IP>:<PORT>/druid/coordinator/v1/lookups/config/{tier}/{id}

All URIs below are assumed to have http://<COORDINATOR_IP>:<PORT> prepended.

If you have NEVER configured lookups before, you MUST post an empty json object {} to /druid/coordinator/v1/lookups/config to initialize the configuration.

These endpoints will return one of the following results:

  • 404 if the resource is not found
  • 400 if there is a problem in the formatting of the request
  • 202 if the request was accepted asynchronously (POST and DELETE)
  • 200 if the request succeeded (GET only)

Configuration propagation behavior

The configuration is propagated to the query serving nodes (broker / router / peon / historical) by the coordinator. The query serving nodes have an internal API for managing lookups on the node and those are used by the coordinator. The coordinator periodically checks if any of the nodes need to load/drop lookups and updates them appropriately.

API for configuring lookups

Bulk update

Lookups can be updated in bulk by posting a JSON object to /druid/coordinator/v1/lookups/config. The format of the json object is as follows:

{
    "<tierName>": {
        "<lookupName>": {
          "version": "<version>",
          "lookupExtractorFactory": {
            "type": "<someExtractorFactoryType>",
            "<someExtractorField>": "<someExtractorValue>"
          }
        }
    }
}

Note that "version" is an arbitrary string assigned by the user, when making updates to existing lookup then user would need to specify a lexicographically higher version.

For example, a config might look something like:

{
  "__default": {
    "country_code": {
      "version": "v0",
      "lookupExtractorFactory": {
        "type": "map",
        "map": {
          "77483": "United States"
        }
      }
    },
    "site_id": {
      "version": "v0",
      "lookupExtractorFactory": {
        "type": "cachedNamespace",
        "extractionNamespace": {
          "type": "jdbc",
          "connectorConfig": {
            "createTables": true,
            "connectURI": "jdbc:mysql:\/\/localhost:3306\/druid",
            "user": "druid",
            "password": "diurd"
          },
          "table": "lookupTable",
          "keyColumn": "country_id",
          "valueColumn": "country_name",
          "tsColumn": "timeColumn"
        },
        "firstCacheTimeout": 120000,
        "injective": true
      }
    },
    "site_id_customer1": {
      "version": "v0",
      "lookupExtractorFactory": {
        "type": "map",
        "map": {
          "847632": "Internal Use Only"
        }
      }
    },
    "site_id_customer2": {
      "version": "v0",
      "lookupExtractorFactory": {
        "type": "map",
        "map": {
          "AHF77": "Home"
        }
      }
    }
  },
  "realtime_customer1": {
    "country_code": {
      "version": "v0",
      "lookupExtractorFactory": {
        "type": "map",
        "map": {
          "77483": "United States"
        }
      }
    },
    "site_id_customer1": {
      "version": "v0",
      "lookupExtractorFactory": {
        "type": "map",
        "map": {
          "847632": "Internal Use Only"
        }
      }
    }
  },
  "realtime_customer2": {
    "country_code": {
      "version": "v0",
      "lookupExtractorFactory": {
        "type": "map",
        "map": {
          "77483": "United States"
        }
      }
    },
    "site_id_customer2": {
      "version": "v0",
      "lookupExtractorFactory": {
        "type": "map",
        "map": {
          "AHF77": "Home"
        }
      }
    }
  }
}

All entries in the map will UPDATE existing entries. No entries will be deleted.

Update Lookup

A POST to a particular lookup extractor factory via /druid/coordinator/v1/lookups/config/{tier}/{id} will update that specific extractor factory.

For example, a post to /druid/coordinator/v1/lookups/config/realtime_customer1/site_id_customer1 might contain the following:

{
  "version": "v1",
  "lookupExtractorFactory": {
    "type": "map",
    "map": {
      "847632": "Internal Use Only"
    }
  }
}

This will replace the site_id_customer1 lookup in the realtime_customer1 with the definition above.

Get Lookup

A GET to a particular lookup extractor factory is accomplished via /druid/coordinator/v1/lookups/{tier}/{id}

Using the prior example, a GET to /druid/coordinator/v1/lookups/config/realtime_customer2/site_id_customer2 should return

{
  "version": "v1",
  "lookupExtractorFactory": {
    "type": "map",
    "map": {
      "AHF77": "Home"
    }
  }
}

Delete Lookup

A DELETE to /druid/coordinator/v1/lookups/config/{tier}/{id} will remove that lookup from the cluster.

List tier names

A GET to /druid/coordinator/v1/lookups/config will return a list of known tier names in the dynamic configuration. To discover a list of tiers currently active in the cluster instead of ones known in the dynamic configuration, the parameter discover=true can be added as per /druid/coordinator/v1/lookups?discover=true.

List lookup names

A GET to /druid/coordinator/v1/lookups/config/{tier} will return a list of known lookup names for that tier.

Additional API related to status of configured lookups

These end points can be used to get the propagation status of configured lookups to lookup nodes such as historicals.

List load status of all lookups

GET /druid/coordinator/v1/lookups/status with optional query parameter detailed.

List load status of lookups in a tier

GET /druid/coordinator/v1/lookups/status/{tier} with optional query parameter detailed.

List load status of single lookup

GET /druid/coordinator/v1/lookups/status/{tier}/{lookup} with optional query parameter detailed.

List lookup state of all nodes

GET /druid/coordinator/v1/lookups/nodeStatus with optional query parameter discover to discover tiers from zookeeper or configured lookup tiers are listed.

List lookup state of nodes in a tier

GET /druid/coordinator/v1/lookups/nodeStatus/{tier}

List lookup state of single node

GET /druid/coordinator/v1/lookups/nodeStatus/{tier}/{host:port}

Internal API

The Peon, Router, Broker, and Historical nodes all have the ability to consume lookup configuration. There is an internal API these nodes use to list/load/drop their lookups starting at /druid/listen/v1/lookups. These follow the same convention for return values as the cluster wide dynamic configuration. Following endpoints can be used for debugging purposes but not otherwise.

Get Lookups

A GET to the node at /druid/listen/v1/lookups will return a json map of all the lookups currently active on the node. The return value will be a json map of the lookups to their extractor factories.

{
  "site_id_customer2": {
    "version": "v1",
    "lookupExtractorFactory": {
      "type": "map",
      "map": {
        "AHF77": "Home"
      }
    }
  }
}

Get Lookup

A GET to the node at /druid/listen/v1/lookups/some_lookup_name will return the LookupExtractorFactory for the lookup identified by some_lookup_name. The return value will be the json representation of the factory.

{
  "version": "v1",
  "lookupExtractorFactory": {
    "type": "map",
    "map": {
      "AHF77": "Home"
    }
  }
}

Configuration

See the coordinator configuration guilde for coordinator configuration

To configure a Broker / Router / Historical / Peon to announce itself as part of a lookup tier, use the druid.zk.paths.lookupTier property.

Property Description Default
druid.lookup.lookupTier The tier for lookups for this node. This is independent of other tiers. __default
druid.lookup.lookupTierIsDatasource For some things like indexing service tasks, the datasource is passed in the runtime properties of a task. This option fetches the tierName from the same value as the datasource for the task. It is suggested to only use this as peon options for the indexing service, if at all. If true, druid.lookup.lookupTier MUST NOT be specified "false"

To configure the behavior of the dynamic configuration manager, use the following properties on the coordinator:

Property Description Default
druid.manager.lookups.hostTimeout Timeout (in ms) PER HOST for processing request 2000(2 seconds)
druid.manager.lookups.allHostTimeout Timeout (in ms) to finish lookup management on all the nodes. 900000(15 mins)
druid.manager.lookups.period How long to pause between management cycles 120000(2 mins)
druid.manager.lookups.threadPoolSize Number of service nodes that can be managed concurrently 10

Saving configuration across restarts

It is possible to save the configuration across restarts such that a node will not have to wait for coordinator action to re-populate its lookups. To do this the following property is set:

Property Description Default
druid.lookup.snapshotWorkingDir Working path used to store snapshot of current lookup configuration, leaving this property null will disable snapshot/bootstrap utility null
druid.lookup.enableLookupSyncOnStartup Enable the lookup synchronization process with coordinator on startup. The queryable nodes will fetch and load the lookups from the coordinator instead of waiting for the coordinator to load the lookups for them. Users may opt to disable this option if there are no lookups configured in the cluster. true
druid.lookup.numLookupLoadingThreads Number of threads for loading the lookups in parallel on startup. This thread pool is destroyed once startup is done. It is not kept during the lifetime of the JVM Available Processors / 2
druid.lookup.coordinatorFetchRetries How many times to retry to fetch the lookup bean list from coordinator, during the sync on startup. 3
druid.lookup.lookupStartRetries How many times to retry to start each lookup, either during the sync on startup, or during the runtime. 3

Introspect a Lookup

Lookup implementations can provide some introspection capabilities by implementing LookupIntrospectHandler. User will send request to /druid/lookups/v1/introspect/{lookupId} to enable introspection on a given lookup.

For instance you can list all the keys/values of a map based lookup by issuing a GET request to /druid/lookups/v1/introspect/{lookupId}/keys" or /druid/lookups/v1/introspect/{lookupId}/values"

Druid version 0.10.0 to 0.10.1 upgrade/downgrade

Overall druid cluster lookups configuration is persisted in metadata store and also individual lookup nodes optionally persist a snapshot of loaded lookups on disk. If upgrading from druid version 0.10.0 to 0.10.1, then migration for all persisted metadata is handled automatically. If downgrading from 0.10.1 to 0.9.0 then lookups updates done via coordinator while 0.10.1 was running, would be lost.