org.apache.flink.table.runtime.functions.table.lookup

Class CachingLookupFunction

java.lang.Object

org.apache.flink.table.functions.UserDefinedFunction

org.apache.flink.table.functions.TableFunction<RowData>

org.apache.flink.table.functions.LookupFunction

org.apache.flink.table.runtime.functions.table.lookup.CachingLookupFunction

All Implemented Interfaces:

Serializable, FunctionDefinition

@Internal
public class CachingLookupFunction
extends LookupFunction

A wrapper function around user-provided lookup function with a cache layer.

This function will check the cache on lookup request and return entries directly on cache hit, otherwise the function will invoke the actual lookup function, and store the entry into the cache after lookup for later use.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static String	LOOKUP_CACHE_METRIC_GROUP_NAME

Constructor Summary

Constructors

Constructor and Description
CachingLookupFunction(LookupCache cache, LookupFunction delegate) Create a CachingLookupFunction.

Method Summary

Modifier and Type	Method and Description
void	close() Tear-down method for user-defined function.
LookupCache	getCache()
Collection<RowData>	lookup(RowData keyRow) Synchronously lookup rows matching the lookup keys.
void	open(FunctionContext context) Open the CachingLookupFunction.

Methods inherited from class org.apache.flink.table.functions.LookupFunction

eval

Methods inherited from class org.apache.flink.table.functions.TableFunction

collect, finish, getKind, getParameterTypes, getResultType, getTypeInference, setCollector

Methods inherited from class org.apache.flink.table.functions.UserDefinedFunction

functionIdentifier, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.flink.table.functions.FunctionDefinition

getRequirements, isDeterministic

Field Detail

LOOKUP_CACHE_METRIC_GROUP_NAME

public static final String LOOKUP_CACHE_METRIC_GROUP_NAME

See Also:

Constant Field Values

Constructor Detail

CachingLookupFunction

public CachingLookupFunction(LookupCache cache,
                             @Nullable
                             LookupFunction delegate)

Create a CachingLookupFunction.

Please note that the cache may not be the final instance serving in this function. The actual cache instance will be retrieved from the LookupCacheManager during open(org.apache.flink.table.functions.FunctionContext).

Method Detail

open

public void open(FunctionContext context)
          throws Exception

Open the CachingLookupFunction.

In order to reduce the memory usage of the cache, LookupCacheManager is used to provide a shared cache instance across subtasks of this function. Here we use UserDefinedFunction.functionIdentifier() as the id of the cache, which is generated by MD5 of serialized bytes of this function. As different subtasks of the function will generate the same MD5, this could promise that they will be served with the same cache instance.

Overrides:

open in class UserDefinedFunction

Throws:

Exception

See Also:

UserDefinedFunction.functionIdentifier()

lookup

public Collection<RowData> lookup(RowData keyRow)
                           throws IOException

Description copied from class: LookupFunction

Synchronously lookup rows matching the lookup keys.

Please note that the returning collection of RowData shouldn't be reused across invocations.

Specified by:

lookup in class LookupFunction

Parameters:

keyRow - - A RowData that wraps lookup keys.

Returns:

A collection of all matching rows in the lookup table.

Throws:

IOException

close

public void close()
           throws Exception

Description copied from class: UserDefinedFunction

Tear-down method for user-defined function. It can be used for clean up work. By default, this method does nothing.

Overrides:

close in class UserDefinedFunction

Throws:

Exception

getCache

@VisibleForTesting
public LookupCache getCache()