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Historical Node Configuration
=============================
For general Historical Node information, see [here](../design/historical.html).

Runtime Configuration
---------------------

The historical node uses several of the global configs in [Configuration](../configuration/index.html) and has the following set of configurations as well:

### Node Configs

|Property|Description|Default|
|--------|-----------|-------|
|`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|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`|8083|
|`druid.tlsPort`|TLS port for HTTPS connector, if [druid.enableTlsPort](../operations/tls-support.html) 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.|8283|
|`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/historical|

### General Configuration

|Property|Description|Default|
|--------|-----------|-------|
|`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 enforces, 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](../operations/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 |

### Storing Segments

|Property|Description|Default|
|--------|-----------|-------|
|`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. This value cannot be NULL or EMPTY. Here is an example `druid.segmentCache.locations=[{"path": "/mnt/druidSegments", "maxSize": 10000}, "freeSpacePercent": 1.0]`. "freeSpacePercent" is optional, if provided then enforces that much of free disk partition space while storing segments. But, it depends on File.getTotalSpace() and File.getFreeSpace() methods, so enable if only if they work for your File System.| none |
|`druid.segmentCache.deleteOnRemove`|Delete segment files from cache once a node is no longer serving a segment.|true|
|`druid.segmentCache.dropSegmentDelayMillis`|How long a node delays before completely dropping segment.|30000 (30 seconds)|
|`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 drop or load concurrently from from deep storage.|10|
|`druid.segmentCache.numBootstrapThreads`|How many segments to load concurrently from local storage at startup.|Same as numLoadingThreads|

In `druid.segmentCache.locations`, *freeSpacePercent* was added because *maxSize* setting is only a theoretical limit and assumes that much space will always be available for storing segments. In case of any druid bug leading to unaccounted segment files left alone on disk or some other process writing stuff to disk, This check can start failing segment loading early before filling up the disk completely and leaving the host usable otherwise.

### Query Configs

#### Concurrent Requests

Druid uses Jetty to serve HTTP requests.

|Property|Description|Default|
|--------|-----------|-------|
|`druid.server.http.numThreads`|Number of threads for HTTP requests.|max(10, (Number of cores * 17) / 16 + 2) + 30|
|`druid.server.http.queueSize`|Size of the worker queue used by Jetty server to temporarily store incoming client connections. If this value is set and a request is rejected by jetty because queue is full then client would observe request failure with TCP connection being closed immediately with a completely empty response from server.|Unbounded|
|`druid.server.http.maxIdleTime`|The Jetty max idle time for a connection.|PT5m|
|`druid.server.http.enableRequestLimit`|If enabled, no requests would be queued in jetty queue and "HTTP 429 Too Many Requests" error response would be sent. |false|
|`druid.server.http.defaultQueryTimeout`|Query timeout in millis, beyond which unfinished queries will be cancelled|300000|
|`druid.server.http.maxQueryTimeout`|Maximum allowed value (in milliseconds) for `timeout` parameter. See [query-context](query-context.html) to know more about `timeout`. Query is rejected if the query context `timeout` is greater than this value. |Long.MAX_VALUE|
|`druid.server.http.maxRequestHeaderSize`|Maximum size of a request header in bytes. Larger headers consume more memory and can make a server more vulnerable to denial of service attacks.|8 * 1024|

#### 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 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.buffer.poolCacheMaxCount`|processing buffer pool caches the buffers for later use, this is the maximum count cache will grow to. note that pool can create more buffers than it can cache if necessary.|Integer.MAX_VALUE|
|`druid.processing.formatString`|Realtime and historical nodes 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.fifo`|If the processing queue should treat tasks of equal priority in a FIFO manner|`false`|
|`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](../querying/groupbyquery.html#server-configuration).

##### Search Query Config

|Property|Description|Default|
|--------|-----------|-------|
|`druid.query.search.maxSearchLimit`|Maximum number of search results to return.|1000|

### Caching

You can optionally only configure caching to be enabled on the historical by setting caching configs here.

|Property|Possible Values|Description|Default|
|--------|---------------|-----------|-------|
|`druid.historical.cache.useCache`|true, false|Enable the cache on the historical.|false|
|`druid.historical.cache.populateCache`|true, false|Populate the cache on the historical.|false|
|`druid.historical.cache.unCacheable`|All druid query types|All query types to not cache.|["groupBy", "select"]|


See [cache configuration](caching.html) for how to configure cache settings.