druid/docs/content/Historical-Config.md

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Historical Node Configuration

For general Historical Node information, see here.

Runtime Configuration

The historical node uses several of the global configs in Configuration and has the following set of configurations as well:

Node Configs

Property	Description	Default
druid.host	The host for the current node. This is used to advertise the current processes location as reachable from another node and should generally be specified such that http://${druid.host}/ could actually talk to this process	none
druid.port	This is the port to actually listen on; unless port mapping is used, this will be the same port as is on druid.host	none
druid.service	The name of the service. This is used as a dimension when emitting metrics and alerts to differentiate between the various services	none

General Configuration

Property	Description	Default
druid.server.tier	A string to name the distribution tier that the storage node belongs to. Many of the rules Coordinator nodes use to manage segments can be keyed on tiers.	_default_tier
druid.server.priority	In a tiered architecture, the priority of the tier, thus allowing control over which nodes are queried. Higher numbers mean higher priority. The default (no priority) works for architecture with no cross replication (tiers that have no data-storage overlap). Data centers typically have equal priority.	0

Storing Segments

Property	Description	Default
druid.segmentCache.locations	Segments assigned to a Historical node are first stored on the local file system (in a disk cache) and then served by the Historical node. These locations define where that local cache resides.	none (no caching)
druid.segmentCache.deleteOnRemove	Delete segment files from cache once a node is no longer serving a segment.	true
druid.segmentCache.dropSegmentDelayMillis	How long a node delays before completely dropping segment.	30000 (30 seconds)
druid.segmentCache.infoDir	Historical nodes keep track of the segments they are serving so that when the process is restarted they can reload the same segments without waiting for the Coordinator to reassign. This path defines where this metadata is kept. Directory will be created if needed.	${first_location}/info_dir
druid.segmentCache.announceIntervalMillis	How frequently to announce segments while segments are loading from cache. Set this value to zero to wait for all segments to be loaded before announcing.	5000 (5 seconds)
druid.segmentCache.numLoadingThreads	How many segments to load concurrently from from deep storage.	1

Query Configs

Concurrent Requests

Druid uses Jetty to serve HTTP requests.

Property	Description	Default
druid.server.http.numThreads	Number of threads for HTTP requests.	10
druid.server.http.maxIdleTime	The Jetty max idle time for a connection.	PT5m

Processing

Property	Description	Default
druid.processing.buffer.sizeBytes	This specifies a buffer size for the storage of intermediate results. The computation engine in both the Historical and Realtime nodes will use a scratch buffer of this size to do all of their intermediate computations off-heap. Larger values allow for more aggregations in a single pass over the data while smaller values can require more passes depending on the query that is being executed.	1073741824 (1GB)
druid.processing.formatString	Realtime and historical nodes use this format string to name their processing threads.	processing-%s
druid.processing.numThreads	The number of processing threads to have available for parallel processing of segments. Our rule of thumb is num_cores - 1, which means that even under heavy load there will still be one core available to do background tasks like talking with ZooKeeper and pulling down segments. If only one core is available, this property defaults to the value 1.	Number of cores - 1 (or 1)
druid.processing.columnCache.sizeBytes	Maximum size in bytes for the dimension value lookup cache. Any value greater than 0 enables the cache. It is currently disabled by default. Enabling the lookup cache can significantly improve the performance of aggregators operating on dimension values, such as the JavaScript aggregator, or cardinality aggregator, but can slow things down if the cache hit rate is low (i.e. dimensions with few repeating values). Enabling it may also require additional garbage collection tuning to avoid long GC pauses.	0 (disabled)

General Query Configuration

GroupBy Query Config

Property	Description	Default
druid.query.groupBy.singleThreaded	Run single threaded group By queries.	false
druid.query.groupBy.maxIntermediateRows	Maximum number of intermediate rows.	50000
druid.query.groupBy.maxResults	Maximum number of results.	500000

Search Query Config

Property	Description	Default
druid.query.search.maxSearchLimit	Maximum number of search results to return.	1000

Caching

You can optionally only configure caching to be enabled on the historical by setting caching configs here.

Property	Possible Values	Description	Default
druid.historical.cache.useCache	true, false	Enable the cache on the historical.	false
druid.historical.cache.populateCache	true, false	Populate the cache on the historical.	false
druid.cache.type	local, memcached	The type of cache to use for queries.	local
druid.cache.unCacheable	All druid query types	All query types to not cache.	["groupBy", "select"]

Local Cache

Property	Description	Default
druid.cache.sizeInBytes	Maximum cache size in bytes. Zero disables caching.	0
druid.cache.initialSize	Initial size of the hashtable backing the cache.	500000
druid.cache.logEvictionCount	If non-zero, log cache eviction every logEvictionCount items.	0

Memcache

Property	Description	Default
druid.cache.expiration	Memcached expiration time.	2592000 (30 days)
druid.cache.timeout	Maximum time in milliseconds to wait for a response from Memcached.	500
druid.cache.hosts	Command separated list of Memcached hosts <host:port>.	none
druid.cache.maxObjectSize	Maximum object size in bytes for a Memcached object.	52428800 (50 MB)
druid.cache.memcachedPrefix	Key prefix for all keys in Memcached.	druid