io.druid.server.lookup

Class LoadingLookup

java.lang.Object

io.druid.query.lookup.LookupExtractor

io.druid.server.lookup.LoadingLookup

public class LoadingLookup
extends LookupExtractor

Loading lookup will load the key\value pair upon request on the key it self, the general algorithm is load key if absent. Once the key/value pair is loaded eviction will occur according to the cache eviction policy. This module comes with two loading cache implementations, the first OnHeapLoadingCacheis onheap backed by a Guava cache implementation, the second OffHeapLoadingCacheis MapDB offheap implementation. Both implementations offer various eviction strategies.

Constructor Summary

Constructors

Constructor and Description
LoadingLookup(DataFetcher dataFetcher, LoadingCache<String,String> loadingCache, LoadingCache<String,List<String>> reverseLoadingCache)

Method Summary

Modifier and Type	Method and Description
String	apply(String key) Apply a particular lookup methodology to the input string
void	close()
byte[]	getCacheKey() Create a cache key for use in results caching
boolean	isOpen()
List<String>	unapply(String value) Provide the reverse mapping from a given value to a list of keys

Methods inherited from class io.druid.query.lookup.LookupExtractor

applyAll, isOneToOne, unapplyAll

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

LoadingLookup

public LoadingLookup(DataFetcher dataFetcher,
                     LoadingCache<String,String> loadingCache,
                     LoadingCache<String,List<String>> reverseLoadingCache)

Method Detail

apply

public String apply(String key)

Description copied from class: LookupExtractor

Apply a particular lookup methodology to the input string

Specified by:

apply in class LookupExtractor

Parameters:

key - The value to apply the lookup to. May not be null

Returns:

The lookup, or null key cannot have the lookup applied to it and should be treated as missing.

unapply

public List<String> unapply(String value)

Description copied from class: LookupExtractor

Provide the reverse mapping from a given value to a list of keys

Specified by:

unapply in class LookupExtractor

Parameters:

value - the value to apply the reverse lookup Null and empty are considered to be the same value = nullToEmpty(value)

Returns:

the list of keys that maps to value or empty list. Note that for the case of a none existing value in the lookup we have to cases either return an empty list OR list with null element. returning an empty list implies that user want to ignore such a lookup value. In the other hand returning a list with the null element implies user want to map the none existing value to the key null.

close

public void close()

isOpen

public boolean isOpen()

getCacheKey

public byte[] getCacheKey()

Description copied from class: LookupExtractor

Create a cache key for use in results caching

Specified by:

getCacheKey in class LookupExtractor

Returns:

A byte array that can be used to uniquely identify if results of a prior lookup can use the cached values