druid/docs/content/configuration/realtime.md

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Realtime Node Configuration

For general Realtime Node information, see here.

Runtime Configuration

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

Node Config

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	InetAddress.getLocalHost().getCanonicalHostName()
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	8084
druid.service	The name of the service. This is used as a dimension when emitting metrics and alerts to differentiate between the various services	druid/realtime

Realtime Operation

Property	Description	Default
druid.publish.type	Where to publish segments. Choices are "noop" or "metadata".	metadata
druid.realtime.specFile	File location of realtime specFile.	none

Storing Intermediate Segments

Property	Description	Default
druid.segmentCache.locations	Where intermediate segments are stored. The maxSize should always be zero.	none

Query Configs

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.numMergeBuffers	The number of direct memory buffers available for merging query results. The buffers are sized by druid.processing.buffer.sizeBytes. This property is effectively a concurrency limit for queries that require merging buffers. If you are using any queries that require merge buffers (currently, just groupBy v2) then you should have at least two of these.	max(2, druid.processing.numThreads / 4)
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)
druid.processing.tmpDir	Path where temporary files created while processing a query should be stored. If specified, this configuration takes priority over the default java.io.tmpdir path.	path represented by java.io.tmpdir

The amount of direct memory needed by Druid is at least druid.processing.buffer.sizeBytes * (druid.processing.numMergeBuffers + druid.processing.numThreads + 1). You can ensure at least this amount of direct memory is available by providing -XX:MaxDirectMemorySize=<VALUE> at the command line.

General Query Configuration

GroupBy Query Config

See groupBy server configuration.

Search Query Config

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

Caching

You can optionally configure caching to be enabled on the realtime node by setting caching configs here.

Property	Possible Values	Description	Default
druid.realtime.cache.useCache	true, false	Enable the cache on the realtime.	false
druid.realtime.cache.populateCache	true, false	Populate the cache on the realtime.	false
druid.realtime.cache.unCacheable	All druid query types	All query types to not cache.	["groupBy", "select"]

See cache configuration for how to configure cache settings.