|`extractionNamespace`|Specifies how to populate the local cache. See below|Yes|-|
|`firstCacheTimeout`|How long to wait (in ms) for the first run of the cache to populate. 0 indicates to not wait|No|`60000` (1 minute)|
|`injective`|If the underlying map is injective (keys and values are unique) then optimizations can occur internally by setting this to `true`|No|`false`|
|`druid.lookup.namespace.cache.type`|Specifies the type of caching to be used by the namespaces. May be one of [`offHeap`, `onHeap`]. `offHeap` uses a temporary file for off-heap storage of the namespace (memory mapped files). `onHeap` stores all cache on the heap in standard java map types.|`onHeap`|
`onHeap` uses `ConcurrentMap`s in the java heap, and thus affects garbage collection and heap sizing.
`offHeap` uses a 10MB on-heap buffer and MapDB using memory-mapped files in the java temporary directory.
So if total `cachedNamespace` lookup size is in excess of 10MB, the extra will be kept in memory as page cache, and paged in and out by general OS tunings.
The `pollPeriod` value specifies the period in ISO 8601 format between checks for replacement data for the lookup. If the source of the lookup is capable of providing a timestamp, the lookup will only be updated if it has changed since the prior tick of `pollPeriod`. A value of 0, an absent parameter, or `null` all mean populate once and do not attempt to look for new data later. Whenever an poll occurs, the updating system will look for a file with the most recent timestamp and assume that one with the most recent data set, replacing the local cache of the lookup data.
The `namespaceParseSpec` can be one of a number of values. Each of the examples below would rename foo to bar, baz to bat, and buck to truck. All parseSpec types assumes each input is delimited by a new line. See below for the types of parseSpec supported.
Only ONE file which matches the search will be used. For most implementations, the discriminator for choosing the URIs is by whichever one reports the most recent timestamp for its modification time.
The `simpleJson` lookupParseSpec does not take any parameters. It is simply a line delimited json file where the field is the key, and the field's value is the value.
*example input*
```json
{"foo": "bar"}
{"baz": "bat"}
{"buck": "truck"}
```
*example namespaceParseSpec*
```json
"namespaceParseSpec":{
"format": "simpleJson"
}
```
## JDBC namespaced lookup
The JDBC lookups will poll a database to populate its local cache. If the `tsColumn` is set it must be able to accept comparisons in the format `'2015-01-01 00:00:00'`. For example, the following must be valid sql for the table `SELECT * FROM some_lookup_table WHERE timestamp_column > '2015-01-01 00:00:00'`. If `tsColumn` is set, the caching service will attempt to only poll values that were written *after* the last sync. If `tsColumn` is not set, the entire table is pulled every time.
|Parameter|Description|Required|Default|
|---------|-----------|--------|-------|
|`namespace`|The namespace to define|Yes||
|`connectorConfig`|The connector config to use|Yes||
|`table`|The table which contains the key value pairs|Yes||
|`keyColumn`|The column in `table` which contains the keys|Yes||
|`valueColumn`|The column in `table` which contains the values|Yes||
|`tsColumn`| The column in `table` which contains when the key was updated|No|Not used|
|`pollPeriod`|How often to poll the DB|No|0 (only once)|
Cached namespace lookups have introspection points at `/keys` and `/values` which return a complete set of the keys and values (respectively) in the lookup. Introspection to `/` returns the entire map. Introspection to `/version` returns the version indicator for the lookup.
