Package com.apple.foundationdb.record.provider.foundationdb.cursors

Class IntersectionMultiCursor<T>

java.lang.Object

com.apple.foundationdb.record.provider.foundationdb.cursors.MergeCursor<T,U,com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>

com.apple.foundationdb.record.provider.foundationdb.cursors.IntersectionMultiCursor<T>

Type Parameters:

T - the type of elements returned by the child cursors

All Implemented Interfaces:

RecordCursor<List<T>>, AutoCloseable, Iterator<List<T>>

@API(EXPERIMENTAL)
public class IntersectionMultiCursor<T>
extends MergeCursor<T,U,com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>

A cursor that implements an intersection of matching elements from a set of cursors all of whom are ordered compatibly. This operates like the IntersectionCursor except that for each set of matching results, this returns a list of all of the elements from all of the child cursors rather than just one.

See Also:

IntersectionCursor

Nested Class Summary

Nested classes/interfaces inherited from interface com.apple.foundationdb.record.RecordCursor

RecordCursor.NoNextReason

Method Summary

Modifier and Type	Method	Description
protected CompletableFuture<List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>>	computeNextResultStates()	Compute the next result states for the cursor based on the status of the existing states.
static <T> IntersectionMultiCursor<T>	create(Function<? super T,? extends List<Object>> comparisonKeyFunction, boolean reverse, List<Function<byte[],RecordCursor<T>>> cursorFunctions, byte[] continuation, FDBStoreTimer timer)	Create an intersection cursor from two or more compatibly-ordered cursors.
protected static <T> List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>	createCursorStates(Function<byte[],RecordCursor<T>> left, Function<byte[],RecordCursor<T>> right, byte[] byteContinuation, Function<? super T,? extends List<Object>> comparisonKeyFunction)
protected static <T> List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>	createCursorStates(List<Function<byte[],RecordCursor<T>>> cursorFunctions, byte[] byteContinuation, Function<? super T,? extends List<Object>> comparisonKeyFunction)
protected Function<? super T,? extends List<Object>>	getComparisonKeyFunction()
com.apple.foundationdb.record.provider.foundationdb.cursors.IntersectionCursorContinuation	getContinuationObject()	Produce a RecordCursorContinuation for this cursor.
protected List<T>	getNextResult(List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>> cursorStates)	Determine the next result to return based on the results of the child cursors.
protected RecordCursor.NoNextReason	mergeNoNextReasons()	Merges all of the cursors and whether they have stopped and returns the "weakest" reason for the result to stop.

Methods inherited from class com.apple.foundationdb.record.provider.foundationdb.cursors.MergeCursor

accept, checkNextStateTimeout, close, getChildContinuations, getContinuation, getCursorStates, getExecutor, getNoNextReason, getStrongestNoNextReason, getTimer, getWeakestNoNextReason, next, onHasNext, onNext, whenAll, whenAny

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Iterator

forEachRemaining, remove

Methods inherited from interface com.apple.foundationdb.record.RecordCursor

asIterator, asList, filter, filterAsync, filterAsyncInstrumented, filterAsyncInstrumented, filterInstrumented, filterInstrumented, first, flatMapPipelined, forEach, forEachAsync, forEachResult, forEachResultAsync, getCount, getNext, hasNext, limitRowsTo, limitTo, map, mapEffect, mapEffect, mapPipelined, orElse, reduce, skip, skipThenLimit

Method Detail

getNextResult

@Nonnull
protected List<T> getNextResult(@Nonnull
                                List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>> cursorStates)

Description copied from class: MergeCursor

Determine the next result to return based on the results of the child cursors. This will be called with the return value of MergeCursor.computeNextResultStates().

Specified by:

getNextResult in class MergeCursor<T,List<T>,com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>

Parameters:

cursorStates - the list of cursors to be included in the result

Returns:

a result somehow combining the results of the input cursors

create

@Nonnull
public static <T> IntersectionMultiCursor<T> create(@Nonnull
                                                    Function<? super T,? extends List<Object>> comparisonKeyFunction,
                                                    boolean reverse,
                                                    @Nonnull
                                                    List<Function<byte[],RecordCursor<T>>> cursorFunctions,
                                                    @Nullable
                                                    byte[] continuation,
                                                    @Nullable
                                                    FDBStoreTimer timer)

Create an intersection cursor from two or more compatibly-ordered cursors. Note that this will throw an error if the list of cursors does not have at least two elements. The returned cursor will return lists of elements, all of which compare equal according to the comparison key function, though they might contain different information outside of what the comparison key function examines. This is useful, for example, if one needs to scan multiple segments of an index and then find all entries that correspond to the same primary key (which can be done by setting a comparison key function that identifies the primary key) and then also apply some filter on all of the entries that come back.

Otherwise, this function returns a cursor that is subject to all of the constraints as an IntersectionCursor returned by its equivalent create() method.

Type Parameters:

T - the type of elements returned by this cursor

Parameters:

comparisonKeyFunction - the function evaluated to compare elements from different cursors

reverse - whether records are returned in descending or ascending order by the comparison key

cursorFunctions - a list of functions to produce RecordCursors from a continuation

continuation - any continuation from a previous scan

timer - the timer used to instrument events

Returns:

a cursor containing all records in all child cursors

computeNextResultStates

@Nonnull
protected CompletableFuture<List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>> computeNextResultStates()

Compute the next result states for the cursor based on the status of the existing states. This should return a (not necessarily proper) sublist of this cursor's cursor states. By default, this assumes the cursors return results in a compatible order based on their comparison key and loops until they all have matching values. Extenders of this class may choose an alternative approach depending on the semantics of that cursor.

To indicate that the intersection cursor should stop, this function should either return an empty list of states or a list containing at least one state that does not have a next item.

Specified by:

computeNextResultStates in class MergeCursor<T,U,com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>

Returns:

the list of states included in the next result

getComparisonKeyFunction

@Nonnull
protected Function<? super T,? extends List<Object>> getComparisonKeyFunction()

mergeNoNextReasons

@Nonnull
protected RecordCursor.NoNextReason mergeNoNextReasons()

Merges all of the cursors and whether they have stopped and returns the "weakest" reason for the result to stop. It will return RecordCursor.NoNextReason.SOURCE_EXHAUSTED if any of the cursors are exhausted. If any of the cursors have stopped due to an in-band limit, it will return an in-band limit as well. Finally, if all of the stopped cursors have done so due to hitting an out-of-band limit, it will return an out-of-band limit as well. Note that, in practice, because an intersection cursor will return false from onHasNext if any of its child cursors have stopped, it is likely that there are only a small number (maybe one or two) cursors that have actually stopped when this method is called (e.g., the first cursor to exhaust its source or the first cursor to hit a limit imposed by the element scan limiter).

Specified by:

mergeNoNextReasons in class MergeCursor<T,U,com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>

Returns:

the weakest reason for stopping

getContinuationObject

@Nonnull
public com.apple.foundationdb.record.provider.foundationdb.cursors.IntersectionCursorContinuation getContinuationObject()

Description copied from class: MergeCursor

Produce a RecordCursorContinuation for this cursor. The super-class itself handles constructing the byte array continuation from this continuation. Most continuations will be based on the continuations of this cursors child cursors. These can be retrieved by calling MergeCursor.getChildContinuations(). This will only be called after MergeCursor.computeNextResultStates() has completed.

Specified by:

getContinuationObject in class MergeCursor<T,U,com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>

Returns:

a RecordCursorContinuation for this cursor based on the state of its child cursors

createCursorStates

@Nonnull
protected static <T> List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>> createCursorStates(@Nonnull
                                                                                                                                   Function<byte[],RecordCursor<T>> left,
                                                                                                                                   @Nonnull
                                                                                                                                   Function<byte[],RecordCursor<T>> right,
                                                                                                                                   @Nullable
                                                                                                                                   byte[] byteContinuation,
                                                                                                                                   @Nonnull
                                                                                                                                   Function<? super T,? extends List<Object>> comparisonKeyFunction)

createCursorStates

@Nonnull
protected static <T> List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>> createCursorStates(@Nonnull
                                                                                                                                   List<Function<byte[],RecordCursor<T>>> cursorFunctions,
                                                                                                                                   @Nullable
                                                                                                                                   byte[] byteContinuation,
                                                                                                                                   @Nonnull
                                                                                                                                   Function<? super T,? extends List<Object>> comparisonKeyFunction)