druid/docs/content/Configuration.md

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Configuring Druid

This describes the common configuration shared by all Druid nodes. These configurations can be defined in the common.runtime.properties file.

JVM Configuration Best Practices

There are three JVM parameters that we set on all of our processes:

1. -Duser.timezone=UTC This sets the default timezone of the JVM to UTC. We always set this and do not test with other default timezones, so local timezones might work, but they also might uncover weird and interesting bugs.
2. -Dfile.encoding=UTF-8 This is similar to timezone, we test assuming UTF-8. Local encodings might work, but they also might result in weird and interesting bugs.
3. -Djava.io.tmpdir=<a path> Various parts of the system that interact with the file system do it via temporary files, and these files can get somewhat large. Many production systems are set up to have small (but fast) /tmp directories, which can be problematic with Druid so we recommend pointing the JVM’s tmp directory to something with a little more meat.

Extensions

Many of Druid's external dependencies can be plugged in as modules. Extensions can be provided using the following configs:

Property	Description	Default
druid.extensions.remoteRepositories	If this is not set to '[]', Druid will try to download extensions at the specified remote repository.	["http://repo1.maven.org/maven2/", "https://metamx.artifactoryonline.com/metamx/pub-libs-releases-local"]
druid.extensions.localRepository	The local maven directory where extensions are installed. If this is set, remoteRepositories is not required.	[]
druid.extensions.coordinates	The list of extensions to include.	[]

Zookeeper

We recommend just setting the base ZK path and the ZK service host, but all ZK paths that Druid uses can be overwritten to absolute paths.

Property	Description	Default
druid.zk.paths.base	Base Zookeeper path.	/druid
druid.zk.service.host	The ZooKeeper hosts to connect to. This is a REQUIRED property and therefore a host address must be supplied.	none

See the Zookeeper page for more information on configuration options for ZK integration.

Request Logging

All nodes that can serve queries can also log the requests they see.

Property	Description	Default
druid.request.logging.type	Choices: noop, file, emitter. How to log every request.	noop

File Request Logging

Daily request logs are stored on disk.

Property	Description	Default
druid.request.logging.dir	Historical, Realtime and Broker nodes maintain request logs of all of the requests they get (interacton is via POST, so normal request logs don’t generally capture information about the actual query), this specifies the directory to store the request logs in	none

Emitter Request Logging

Every request is emitted to some external location.

Property	Description	Default
druid.request.logging.feed	Feed name for requests.	none

Enabling Metrics

Druid nodes periodically emit metrics and different metrics monitors can be included. Each node can overwrite the default list of monitors.

Property	Description	Default
druid.monitoring.emissionPeriod	How often metrics are emitted.	PT1m
druid.monitoring.monitors	Sets list of Druid monitors used by a node. Each monitor is specified as com.metamx.metrics.<monitor-name> (see below for names and more information). For example, you can specify monitors for a Broker with druid.monitoring.monitors=["com.metamx.metrics.SysMonitor","com.metamx.metrics.JvmMonitor"].	none (no monitors)

The following monitors are available:

• CacheMonitor – Emits metrics (to logs) about the segment results cache for Historical and Broker nodes. Reports typical cache statistics include hits, misses, rates, and size (bytes and number of entries), as well as timeouts and and errors.
• SysMonitor – This uses the SIGAR library to report on various system activities and statuses.
• ServerMonitor – Reports statistics on Historical nodes.
• JvmMonitor – Reports JVM-related statistics.
• RealtimeMetricsMonitor – Reports statistics on Realtime nodes.

Emitting Metrics

The Druid servers emit various metrics and alerts via something we call an Emitter. There are three emitter implementations included with the code, a "noop" emitter, one that just logs to log4j ("logging", which is used by default if no emitter is specified) and one that does POSTs of JSON events to a server ("http"). The properties for using the logging emitter are described below.

Property	Description	Default
druid.emitter	Setting this value to "noop", "logging", or "http" will instantialize one of the emitter modules.	logging

Logging Emitter Module

Property	Description	Default
druid.emitter.logging.loggerClass	Choices: HttpPostEmitter, LoggingEmitter, NoopServiceEmitter, ServiceEmitter. The class used for logging.	LoggingEmitter
druid.emitter.logging.logLevel	Choices: debug, info, warn, error. The log level at which message are logged.	info

Http Emitter Module

Property	Description	Default
druid.emitter.http.timeOut	The timeout for data reads.	PT5M
druid.emitter.http.flushMillis	How often to internal message buffer is flushed (data is sent).	60000
druid.emitter.http.flushCount	How many messages can the internal message buffer hold before flushing (sending).	500
druid.emitter.http.recipientBaseUrl	The base URL to emit messages to. Druid will POST JSON to be consumed at the HTTP endpoint specified by this property.	none

Metadata Storage

These properties specify the jdbc connection and other configuration around the metadata storage. The only processes that connect to the metadata storage with these properties are the Coordinator and Indexing service.

Property	Description	Default
druid.metadata.storage.type	The type of metadata storage to use. Choose from "mysql", "postgres", or "derby".	derby
druid.metadata.storage.connector.user	The username to connect with.	none
druid.metadata.storage.connector.password	The password to connect with.	none
druid.metadata.storage.connector.createTables	If Druid requires a table and it doesn't exist, create it?	true
druid.metadata.storage.connector.useValidationQuery	Validate a table with a query.	false
druid.metadata.storage.connector.validationQuery	The query to validate with.	SELECT 1
druid.metadata.storage.tables.base	The base name for tables.	druid
druid.metadata.storage.tables.segmentTable	The table to use to look for segments.	druid_segments
druid.metadata.storage.tables.ruleTable	The table to use to look for segment load/drop rules.	druid_rules
druid.metadata.storage.tables.configTable	The table to use to look for configs.	druid_config
druid.metadata.storage.tables.tasks	Used by the indexing service to store tasks.	druid_tasks
druid.metadata.storage.tables.taskLog	Used by the indexing service to store task logs.	druid_taskLog
druid.metadata.storage.tables.taskLock	Used by the indexing service to store task locks.	druid_taskLock

Deep Storage

The configurations concern how to push and pull Segments from deep storage.

Property	Description	Default
druid.storage.type	Choices:local, noop, s3, hdfs, c*. The type of deep storage to use.	local

Local Deep Storage

Local deep storage uses the local filesystem.

Property	Description	Default
druid.storage.storageDirectory	Directory on disk to use as deep storage.	/tmp/druid/localStorage

Noop Deep Storage

This deep storage doesn't do anything. There are no configs.

S3 Deep Storage

This deep storage is used to interface with Amazon's S3.

Property	Description	Default
druid.s3.accessKey	The access key to use to access S3.	none
druid.s3.secretKey	The secret key to use to access S3.	none
druid.storage.bucket	S3 bucket name.	none
druid.storage.baseKey	S3 object key prefix for storage.	none
druid.storage.disableAcl	Boolean flag for ACL.	false
druid.storage.archiveBucket	S3 bucket name for archiving when running the indexing-service archive task.	none
druid.storage.archiveBaseKey	S3 object key prefix for archiving.	none

HDFS Deep Storage

This deep storage is used to interface with HDFS.

Property	Description	Default
druid.storage.storageDirectory	HDFS directory to use as deep storage.	none

Cassandra Deep Storage

This deep storage is used to interface with Cassandra.

Property	Description	Default
druid.storage.host	Cassandra host.	none
druid.storage.keyspace	Cassandra key space.	none

Caching

If you are using a distributed cache such as memcached, you can include the configuration here.

Property	Description	Default
druid.cache.type	local, memcached	The type of cache to use for queries.
druid.cache.unCacheable	All druid query types	All query types to not cache.

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

Indexing Service Discovery

This config is used to find the Indexing Service using Curator service discovery. Only required if you are actually running an indexing service.

Property	Description	Default
druid.selectors.indexing.serviceName	The druid.service name of the indexing service Overlord node. To start the Overlord with a different name, set it with this property.	overlord

Announcing Segments

You can optionally configure how to announce and unannounce Znodes in ZooKeeper (using Curator). For normal operations you do not need to override any of these configs.

Data Segment Announcer

Data segment announcers are used to announce segments.

Property	Description	Default
druid.announcer.type	Choices: legacy or batch. The type of data segment announcer to use.	batch

Single Data Segment Announcer

In legacy Druid, each segment served by a node would be announced as an individual Znode.

Batch Data Segment Announcer

In current Druid, multiple data segments may be announced under the same Znode.

Property	Description	Default
druid.announcer.segmentsPerNode	Each Znode contains info for up to this many segments.	50
druid.announcer.maxBytesPerNode	Max byte size for Znode.	524288