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. To issue queries in a non-UTC timezone, see [query granularities](../querying/granularities.html#period-granularities)
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.
4.`-Djava.util.logging.manager=org.apache.logging.log4j.jul.LogManager` This allows log4j2 to handle logs for non-log4j2 components (like jetty) which use standard java logging.
### Extensions
Many of Druid's external dependencies can be plugged in as modules. Extensions can be provided using the following configs:
|`druid.extensions.directory`|The root extension directory where user can put extensions related files. Druid will load extensions stored under this directory.|`extensions` (This is a relative path to Druid's working directory)|
|`druid.extensions.hadoopDependenciesDir`|The root hadoop dependencies directory where user can put hadoop related dependencies files. Druid will load the dependencies based on the hadoop coordinate specified in the hadoop index task.|`hadoop-dependencies` (This is a relative path to Druid's working directory|
|`druid.extensions.loadList`|A JSON array of extensions to load from extension directories by Druid. If it is not specified, its value will be `null` and Druid will load all the extensions under `druid.extensions.directory`. If its value is empty list `[]`, then no extensions will be loaded at all. It is also allowed to specify absolute path of other custom extensions not stored in the common extensions directory.|null|
|`druid.extensions.searchCurrentClassloader`|This is a boolean flag that determines if Druid will search the main classloader for extensions. It defaults to true but can be turned off if you have reason to not automatically add all modules on the classpath.|true|
|`druid.extensions.hadoopContainerDruidClasspath`|Hadoop Indexing launches hadoop jobs and this configuration provides way to explicitly set the user classpath for the hadoop job. By default this is computed automatically by druid based on the druid process classpath and set of extensions. However, sometimes you might want to be explicit to resolve dependency conflicts between druid and hadoop.|null|
|`druid.extensions.addExtensionsToHadoopContainer`|Only applicable if `druid.extensions.hadoopContainerDruidClasspath` is provided. If set to true, then extensions specified in the loadList are added to hadoop container classpath. Note that when `druid.extensions.hadoopContainerDruidClasspath` is not provided then extensions are always added to hadoop container classpath.|false|
|`druid.modules.excludeList`|A JSON array of canonical class names (e. g. `"io.druid.somepackage.SomeModule"`) of module classes which shouldn't be loaded, even if they are found in extensions specified by `druid.extensions.loadList`, or in the list of core modules specified to be loaded on a particular Druid node type. Useful when some useful extension contains some module, which shouldn't be loaded on some Druid node type because some dependencies of that module couldn't be satisfied.|[]|
|`druid.zk.service.acl`|Boolean flag for whether or not to enable ACL security for ZooKeeper. If ACL is enabled, zNode creators will have all permissions.|`false`|
Druid interacts with ZK through a set of standard path configurations. We recommend just setting the base ZK path, but all ZK paths that Druid uses can be overwritten to absolute paths.
|`druid.zk.paths.indexer.tasksPath`|Used to assign tasks to middle managers.|`${druid.zk.paths.indexer.base}/tasks`|
|`druid.zk.paths.indexer.statusPath`|Parent path for announcement of task statuses.|`${druid.zk.paths.indexer.base}/status`|
|`druid.zk.paths.indexer.leaderLatchPath`|Used for Overlord leader election.|`${druid.zk.paths.indexer.base}/leaderLatchPath`|
If `druid.zk.paths.base` and `druid.zk.paths.indexer.base` are both set, and none of the other `druid.zk.paths.*` or `druid.zk.paths.indexer.*` values are set, then the other properties will be evaluated relative to their respective `base`.
For example, if `druid.zk.paths.base` is set to `/druid1` and `druid.zk.paths.indexer.base` is set to `/druid2` then `druid.zk.paths.announcementsPath` will default to `/druid1/announcements` while `druid.zk.paths.indexer.announcementsPath` will default to `/druid2/announcements`.
[Exhibitor](https://github.com/Netflix/exhibitor/wiki) is a supervisor system for ZooKeeper.
Exhibitor can dynamically scale-up/down the cluster of ZooKeeper servers.
Druid can update self-owned list of ZooKeeper servers through Exhibitor without restarting.
That is, it allows Druid to keep the connections of Exhibitor-supervised ZooKeeper servers.
|Property|Description|Default|
|--------|-----------|-------|
|`druid.exhibitor.service.hosts`|A JSON array which contains the hostnames of Exhibitor instances. Please specify this property if you want to use Exhibitor-supervised cluster.|none|
|`druid.exhibitor.service.port`|The REST port used to connect to Exhibitor.|`8080`|
|`druid.exhibitor.service.restUriPath`|The path of the REST call used to get the server set.|`/exhibitor/v1/cluster/list`|
|`druid.exhibitor.service.useSsl`|Boolean flag for whether or not to use https protocol.|`false`|
|`druid.exhibitor.service.pollingMs`|How ofter to poll the exhibitors for the list|`10000`|
Note that `druid.zk.service.host` is used as a backup in case an Exhibitor instance can't be contacted and therefore should still be set.
All nodes can log debugging information on startup.
|Property|Description|Default|
|--------|-----------|-------|
|`druid.startup.logging.logProperties`|Log all properties on startup (from common.runtime.properties, runtime.properties, and the JVM command line).|false|
Note that, you can enable sending all the HTTP requests to log by setting "io.druid.jetty.RequestLog" to DEBUG level. See [Logging](../configuration/logging.html)
|`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|
Every request is logged via SLF4J. Queries are serialized into JSON in the log message regardless of the SJF4J format specification. They will be logged under the class `io.druid.server.log.LoggingRequestLogger`.
|Property|Description|Default|
|--------|-----------|-------|
|`druid.request.logging.setMDC`|If MDC entries should be set in the log entry. Your logging setup still has to be configured to handle MDC to format this data|false|
|`druid.request.logging.setContextMDC`|If the druid query `context` should be added to the MDC entries. Has no effect unless `setMDC` is `true`|false|
MDC fields populated with `setMDC`:
|MDC field|Description|
|---------|-----------|
|`queryId` |The query ID|
|`dataSource`|The datasource the query was against|
|`queryType` |The type of the query|
|`hasFilters`|If the query has any filters|
|`remoteAddr`|The remote address of the requesting client|
Filtered Request Logger filters requests based on a configurable query/time threshold. Only request logs where query/time is above the threshold are emitted.
|Property|Description|Default|
|--------|-----------|-------|
|`druid.request.logging.queryTimeThresholdMs`|Threshold value for query/time in milliseconds.|0 i.e no filtering|
|`druid.request.logging.delegate`|Delegate request logger to log requests.|none|
#### Composite Request Logging
Composite Request Logger emits request logs to multiple request loggers.
|Property|Description|Default|
|--------|-----------|-------|
|`druid.request.logging.loggerProviders`|List of request loggers for emitting request logs.|none|
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. 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:
|Name|Description|
|----|-----------|
|`io.druid.client.cache.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.|
|`com.metamx.metrics.SysMonitor`|This uses the [SIGAR library](http://www.hyperic.com/products/sigar) to report on various system activities and statuses.|
The Druid servers [emit various metrics](../operations/metrics.html) 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.
|`druid.emitter`|Setting this value to "noop", "logging", or "http" will initialize one of the emitter modules. value "composing" can be used to initialize multiple emitter modules. |noop|
|`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.recipientBaseUrl`|The base URL to emit messages to. Druid will POST JSON to be consumed at the HTTP endpoint specified by this property.|none|
To use graphite as emitter set `druid.emitter=graphite`. For configuration details please follow this [link](../development/extensions-contrib/graphite.html).
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](../design/coordinator.html), [Indexing service](../design/indexing-service.html) and [Realtime Nodes](../design/realtime.html).
|`druid.metadata.storage.connector.password`|The [Password Provider](../operations/password-provider.html) or String password used to connect with.|none|
|<code>druid.(broker|historical|realtime).cache.unCacheable</code>|All druid query types|All query types to not cache.|["groupBy", "select"]|
|<code>druid.(broker|historical|realtime).cache.useCache</code>|Whether to use cache for getting query results.|false|
|<code>druid.(broker|historical|realtime).cache.populateCache</code>|Whether to populate cache.|false|
|`druid.cache.sizeInBytes`|Maximum cache size in bytes. You must set this if you enabled populateCache/useCache, or else cache size of zero wouldn't really cache anything.|0|
|`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](../design/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. |druid/overlord|
This config is used to find the [Coordinator](../design/coordinator.html) using Curator service discovery. This config is used by the realtime indexing nodes to get information about the segments loaded in the cluster.
|Property|Description|Default|
|--------|-----------|-------|
|`druid.selectors.coordinator.serviceName`|The druid.service name of the coordinator node. To start the Coordinator with a different name, set it with this property. |druid/coordinator|
You can configure how to announce and unannounce Znodes in ZooKeeper (using Curator). For normal operations you do not need to override any of these configs.
|`druid.announcer.skipDimensionsAndMetrics`|Skip Dimensions and Metrics list from segment announcements. NOTE: Enabling this will also remove the dimensions and metrics list from coordinator and broker endpoints.|false|
|`druid.announcer.skipLoadSpec`|Skip segment LoadSpec from segment announcements. NOTE: Enabling this will also remove the loadspec from coordinator and broker endpoints.|false|
|`druid.javascript.enabled`|Set to "true" to enable JavaScript functionality. This affects the JavaScript parser, filter, extractionFn, aggregator, post-aggregator, router strategy, and worker selection strategy.|false|
JavaScript-based functionality is disabled by default. Please refer to the Druid <ahref="../development/javascript.html">JavaScript programming guide</a> for guidelines about using Druid's JavaScript functionality, including instructions on how to enable it.
