Table of Contents

Realtime Process Configuration

For general Apache Druid (incubating) Realtime Process information, see here.

Runtime Configuration

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

Process Config

Property Description Default
druid.host The host for the current process. This is used to advertise the current processes location as reachable from another process and should generally be specified such that http://${druid.host}/ could actually talk to this process InetAddress.getLocalHost().getCanonicalHostName()
druid.plaintextPort 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.tlsPort TLS port for HTTPS connector, if druid.enableTlsPort is set then this config will be used. If druid.host contains port then that port will be ignored. This should be a non-negative Integer. 8284
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 processes 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. auto (max 1GB)
druid.processing.formatString Realtime and Historical processes 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 process 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. ["select"]
druid.realtime.cache.maxEntrySize positive integer or -1 Maximum size of an individual cache entry (processed results for one segment), in bytes, or -1 for unlimited. 1000000 (1MB)

See cache configuration for how to configure cache settings.