org.apache.druid.query.groupby.epinephelinae

Interface Grouper<KeyType>

Type Parameters:

KeyType - type of the key that will be passed in

All Superinterfaces:

AutoCloseable, Closeable

All Known Subinterfaces:

IntGrouper

All Known Implementing Classes:

AbstractBufferHashGrouper, BufferArrayGrouper, BufferHashGrouper, ConcurrentGrouper, LimitedBufferHashGrouper, SpillingGrouper, StreamingMergeSortedGrouper

public interface Grouper<KeyType>
extends Closeable

Groupers aggregate metrics from rows that they typically get from a ColumnSelectorFactory, under grouping keys that some outside driver is passing in. They can also iterate over the grouped rows after the aggregation is done. They work sort of like a map of KeyType to aggregated values, except they don't support random lookups. See VectorGrouper for a vectorized version.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	Grouper.BufferComparator
static interface	Grouper.Entry<T>
static interface	Grouper.KeySerde<T> Possibly-stateful object responsible for serde and comparison of keys.
static interface	Grouper.KeySerdeFactory<T>

Method Summary

Modifier and Type	Method and Description
default AggregateResult	aggregate(KeyType key) Aggregate the current row with the provided key.
AggregateResult	aggregate(KeyType key, int keyHash) Aggregate the current row with the provided key.
void	close() Close the grouper and release associated resources.
default ToIntFunction<KeyType>	hashFunction()
void	init() Initialize the grouper.
boolean	isInitialized() Check this grouper is initialized or not.
CloseableIterator<Grouper.Entry<KeyType>>	iterator(boolean sorted) Iterate through entries.
void	reset() Reset the grouper to its initial state.

Method Detail

init

void init()

Initialize the grouper. This method needs to be called before calling aggregate(Object) and aggregate(Object, int).

isInitialized

boolean isInitialized()

Check this grouper is initialized or not.

Returns:

true if the grouper is already initialized, otherwise false.

aggregate

AggregateResult aggregate(KeyType key,
                          int keyHash)

Aggregate the current row with the provided key. Some implementations are thread-safe and some are not.

Parameters:

key - key object

keyHash - result of hashFunction() on the key

Returns:

result that is ok if the row was aggregated, not ok if a resource limit was hit

aggregate

default AggregateResult aggregate(KeyType key)

Aggregate the current row with the provided key. Some implementations are thread-safe and some are not.

Parameters:

key - key

Returns:

result that is ok if the row was aggregated, not ok if a resource limit was hit

reset

void reset()

Reset the grouper to its initial state.

hashFunction

default ToIntFunction<KeyType> hashFunction()

close

void close()

Close the grouper and release associated resources.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

iterator

CloseableIterator<Grouper.Entry<KeyType>> iterator(boolean sorted)

Iterate through entries.

Some implementations allow writes even after this method is called. After you are done with the iterator returned by this method, you should either call close() (if you are done with the Grouper) or reset() (if you want to reuse it). Some implementations allow calling iterator(boolean) again if you want another iterator. But, this method must not be called by multiple threads concurrently.

If "sorted" is true then the iterator will return sorted results. It will use KeyType's natural ordering on deserialized objects, and will use the Grouper.KeySerde.bufferComparator() on serialized objects. Woe be unto you if these comparators are not equivalent.

Callers must process and discard the returned Grouper.Entrys immediately because some implementations can reuse the key objects.

Parameters:

sorted - return sorted results

Returns:

entry iterator