This describes the basic server configuration that is loaded by all Druid server processes; the same file is loaded by all. See also the JSON "specFile" descriptions in [Realtime](Realtime.html) and [Batch-ingestion](Batch-ingestion.html).
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.
As of Druid v0.6, most core Druid functionality has been compartmentalized into modules. There are a set of default modules that may apply to any node type, and there are specific modules for the different node types. Default modules are __lazily instantiated__. Each module has its own set of configuration.
This page describes the configuration of the default modules. Node-specific configuration is discussed on each node's respective page. In addition, you can add custom modules to [extend Druid](Modules.html).
Configuration of the various modules is done via Java properties. These can either be provided as `-D` system properties on the java command line or they can be passed in via a file called `runtime.properties` that exists on the classpath.
The Druid servers emit various metrics and alerts via something we call an Emitter. There are two emitter implementations included with the code, 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.
|`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|
|`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|
|`druid.broker.http.numConnections`|Size of connection pool for the Broker to connect to historical and real-time nodes. If there are more queries than this number that all need to speak to the same node, then they will queue up.|5|
|`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)|
|`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)|
* 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](http://www.hyperic.com/products/sigar) to report on various system activities and statuses.
* ServerMonitor – Reports statistics on Historical nodes.
|`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://${druid.host}/` could actually talk to this process|none|
|`druid.port`|This is the port to actually listen on; unless port mapping is used, this will be the same port as is on `druid.host`|none|
|`druid.service`|The name of the service. This is used as a dimension when emitting metrics and alerts to differentiate between the various services|none|
|`druid.server.maxSize`|The maximum number of bytes-worth of segments that the node wants assigned to it. This is not a limit that Historical nodes actually enforce, just a value published to the Coordinator node so it can plan accordingly.|0|
|`druid.server.tier`| A string to name the distribution tier that the storage node belongs to. Many of the [rules Coordinator nodes use](Rule-Configuration.html) to manage segments can be keyed on tiers. | `_default_tier` |
|`druid.server.priority`|In a tiered architecture, the priority of the tier, thus allowing control over which nodes are queried. Higher numbers mean higher priority. The default (no priority) works for architecture with no cross replication (tiers that have no data-storage overlap). Data centers typically have equal priority. | 0 |
|`druid.segmentCache.locations`|Segments assigned to a Historical node are first stored on the local file system (in a disk cache) and then served by the Historical node. These locations define where that local cache resides. | none (no caching) |
|`druid.segmentCache.infoDir`|Historical nodes keep track of the segments they are serving so that when the process is restarted they can reload the same segments without waiting for the Coordinator to reassign. This path defines where this metadata is kept. Directory will be created if needed.|${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|
|`druid.server.http.numThreads`|Number of threads for HTTP requests.|10|
|`druid.server.http.maxIdleTime`|The Jetty max idle time for a connection.|PT5m|
### Queryable Module
This module is used by all nodes that can serve queries.
|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|
### Query Runner Factory Module
This module is required by nodes that can serve queries.
|`druid.query.chunkPeriod`|Long-interval queries (of any type) may be broken into shorter interval queries, reducing the impact on resources. Use ISO 8601 periods. For example, if this property is set to `P1M` (one month), then a query covering a year would be broken into 12 smaller queries. |0 (off)|
|`druid.discovery.curator.path`|Services announce themselves under this ZooKeeper path.|/druid/discovery|
#### Indexing Service Discovery Module
This module is used to find the [Indexing Service](Indexing-Service.html) using Curator service discovery.
|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|
These properties specify the jdbc connection and other configuration around the database. The only processes that connect to the DB with these properties are the [Coordinator](Coordinator.html) and [Indexing service](Indexing-service.html). This is tested on metadata storage.
