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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

Druid uses [Curator](http://curator.incubator.apache.org/) for all [Zookeeper](http://zookeeper.apache.org/) interactions.

|Property|Description|Default|
|--------|-----------|-------|
|`druid.zk.service.host`|The ZooKeeper hosts to connect to. This is a REQUIRED property and therefore a host address must be supplied.|none|
|`druid.zk.service.sessionTimeoutMs`|ZooKeeper session timeout, in milliseconds.|30000|
|`druid.curator.compress`|Boolean flag for whether or not created Znodes should be compressed.|false|

We recommend just setting the base ZK path, but all ZK paths that Druid uses can be overwritten.

|Property|Description|Default|
|--------|-----------|-------|
|`druid.zk.paths.base`|Base Zookeeper path.|druid|
|`druid.zk.paths.propertiesPath`|Zookeeper properties path.|druid/properties|
|`druid.zk.paths.announcementsPath`|Druid node announcement path.|druid/announcements|
|`druid.zk.paths.liveSegmentsPath`|Current path for where Druid nodes announce their segments.|druid/segments|
|`druid.zk.paths.loadQueuePath`|Entries here cause historical nodes to load and drop segments.|druid/loadQueue|
|`druid.zk.paths.coordinatorPath`|Used by the coordinator for leader election.|druid/coordinator|
|`druid.zk.paths.servedSegmentsPath`|@Deprecated. Legacy path for where Druid nodes announce their segments.|druid/servedSegments|

The indexing service also uses its own set of paths. These configs can be included in the common configuration.

|Property|Description|Default|
|--------|-----------|-------|
|`druid.zk.paths.indexer.announcementsPath`|Middle managers announce themselves here.|druid/indexer/announcements|
|`druid.zk.paths.indexer.tasksPath`|Used to assign tasks to middle managers.|druid/indexer/tasks|
|`druid.zk.paths.indexer.statusPath`|Parent path for announcement of task statuses.|druid/indexer/status|
|`druid.zk.paths.indexer.leaderLatchPath`|Used for Overlord leader election.|druid/indexer/leaderLatchPath|

The following path is used service discovery.

|Property|Description|Default|
|--------|-----------|-------|
|`druid.discovery.curator.path`|Services announce themselves under this ZooKeeper path.|/druid/discovery|

### 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 &ndash; 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 &ndash; This uses the [SIGAR library](http://www.hyperic.com/products/sigar) to report on various system activities and statuses.
* ServerMonitor &ndash; Reports statistics on Historical nodes.
* JvmMonitor &ndash; Reports JVM-related statistics.
* RealtimeMetricsMonitor &ndash; 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](Coordinator.html) and [Indexing service](Indexing-service.html).

|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](Segments.html) 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.|`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](https://code.google.com/p/memcached/wiki/NewCommands#Standard_Protocol).|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](Indexing-Service.html) 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|