org.apache.druid.query

Interface CacheStrategy<T,CacheType,QueryType extends Query<T>>

public interface CacheStrategy<T,CacheType,QueryType extends Query<T>>

Handles caching-related tasks for a particular query type. Generally returned by the toolchest method QueryToolChest.getCacheStrategy(QueryType).

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	CacheStrategy.AddToResultFunction

Method Summary

Modifier and Type	Method and Description
byte[]	computeCacheKey(QueryType query) Computes the per-segment cache key for the given query.
byte[]	computeResultLevelCacheKey(QueryType query) Computes the result-level cache key for the given query.
static void	fetchAggregatorsFromCache(List<AggregatorFactory> aggregators, Iterator<Object> resultIter, boolean isResultLevelCache, CacheStrategy.AddToResultFunction addToResultFunction) Helper function used by TopN, GroupBy, Timeseries queries in pullFromCache(boolean).
com.fasterxml.jackson.core.type.TypeReference<CacheType>	getCacheObjectClazz() Returns the class type of what is used in the cache
boolean	isCacheable(QueryType query, boolean willMergeRunners) Returns whether the given query is cacheable or not.
com.google.common.base.Function<T,CacheType>	prepareForCache(boolean isResultLevelCache) Returns a function that converts from the QueryType's result type to something cacheable.
default com.google.common.base.Function<T,CacheType>	prepareForSegmentLevelCache()
com.google.common.base.Function<CacheType,T>	pullFromCache(boolean isResultLevelCache) A function that does the inverse of the operation that the function prepareForCache returns
default com.google.common.base.Function<CacheType,T>	pullFromSegmentLevelCache()

Method Detail

isCacheable

boolean isCacheable(QueryType query,
                    boolean willMergeRunners)

Returns whether the given query is cacheable or not. The willMergeRunners parameter can be used for distinguishing the caller is a broker or a data node.

Parameters:

query - the query to be cached

willMergeRunners - indicates that QueryRunnerFactory.mergeRunners(QueryProcessingPool, Iterable) will be called on the cached by-segment results

Returns:

true if the query is cacheable, otherwise false.

computeCacheKey

byte[] computeCacheKey(QueryType query)

Computes the per-segment cache key for the given query. Because this is a per-segment cache key, it should only include parts of the query that affect the results for a specific segment (i.e., the results returned from QueryRunnerFactory.createRunner(org.apache.druid.segment.Segment)).

Parameters:

query - the query to be cached

Returns:

the per-segment cache key

computeResultLevelCacheKey

byte[] computeResultLevelCacheKey(QueryType query)

Computes the result-level cache key for the given query. The result-level cache will tack on datasource and interval details, so this key does not need to include datasource and interval. But it should include anything else that might affect the results of the query. Some implementations will need to include query parameters that are not used in computeCacheKey(QueryType) for the same query.

Parameters:

query - the query to be cached

Returns:

the result-level cache key

getCacheObjectClazz

com.fasterxml.jackson.core.type.TypeReference<CacheType> getCacheObjectClazz()

Returns the class type of what is used in the cache

Returns:

Returns the class type of what is used in the cache

prepareForCache

com.google.common.base.Function<T,CacheType> prepareForCache(boolean isResultLevelCache)

Returns a function that converts from the QueryType's result type to something cacheable.

The resulting function must be thread-safe.

Parameters:

isResultLevelCache - indicates whether the function is invoked for result-level caching or segment-level caching

Returns:

a thread-safe function that converts the QueryType's result type into something cacheable

pullFromCache

com.google.common.base.Function<CacheType,T> pullFromCache(boolean isResultLevelCache)

A function that does the inverse of the operation that the function prepareForCache returns

Parameters:

isResultLevelCache - indicates whether the function is invoked for result-level caching or segment-level caching

Returns:

A function that does the inverse of the operation that the function prepareForCache returns

prepareForSegmentLevelCache

default com.google.common.base.Function<T,CacheType> prepareForSegmentLevelCache()

pullFromSegmentLevelCache

default com.google.common.base.Function<CacheType,T> pullFromSegmentLevelCache()

fetchAggregatorsFromCache

static void fetchAggregatorsFromCache(List<AggregatorFactory> aggregators,
                                      Iterator<Object> resultIter,
                                      boolean isResultLevelCache,
                                      CacheStrategy.AddToResultFunction addToResultFunction)

Helper function used by TopN, GroupBy, Timeseries queries in pullFromCache(boolean). When using the result level cache, the agg values seen here are finalized values generated by AggregatorFactory.finalizeComputation(). These finalized values are deserialized from the cache as generic Objects, which will later be reserialized and returned to the user without further modification. Because the agg values are deserialized as generic Objects, the values are subject to the same type consistency issues handled by DimensionHandlerUtils.convertObjectToType() in the pullFromCache implementations for dimension values (e.g., a Float would become Double).