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

Class IntersectionMultiCursor<T>

java.lang.Object

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(value=EXPERIMENTAL)
public class IntersectionMultiCursor<T>
extends Object

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 and Description
boolean	accept(RecordCursorVisitor visitor) Accept a visit from hierarchical visitor, which implements RecordCursorVisitor.
void	close()
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()
byte[]	getContinuation() Deprecated.
com.apple.foundationdb.record.provider.foundationdb.cursors.IntersectionCursorContinuation	getContinuationObject() Produce a RecordCursorContinuation for this cursor.
Executor	getExecutor()
RecordCursor.NoNextReason	getNoNextReason() Deprecated.
FDBStoreTimer	getTimer() Get the FDBStoreTimer used to instrument events of this cursor.
protected RecordCursor.NoNextReason	mergeNoNextReasons() Merges all of the cursors and whether they have stopped and returns the "weakest" reason for the result to stop.
U	next() Deprecated.
CompletableFuture<Boolean>	onHasNext() Deprecated.
CompletableFuture<RecordCursorResult<U>>	onNext() Asynchronously return the next result from this cursor.

Methods inherited from class java.lang.Object

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

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

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

Methods inherited from interface java.util.Iterator

forEachRemaining, remove

Method Detail

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.

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).

Returns:

the weakest reason for stopping

getContinuationObject

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

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 getChildContinuations(). This will only be called after computeNextResultStates() has completed.

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)

onNext

@Nonnull
public CompletableFuture<RecordCursorResult<U>> onNext()

Description copied from interface: RecordCursor

Asynchronously return the next result from this cursor. When complete, the future will contain a RecordCursorResult, which represents exactly one of the following:

1. The next object of type T produced by the cursor. In addition to the next record, this result includes a RecordCursorContinuation that can be used to continue the cursor after the last record returned. The returned continuation is guaranteed not to be an "end continuation" representing the end of the cursor: specifically, RecordCursorContinuation.isEnd() is always false on the returned continuation.
2. The fact that the cursor is stopped and cannot produce another record and a RecordCursor.NoNextReason that explains why no record could be produced. The result include a continuation that can be used to continue the cursor after the last record returned. If the result's NoNextReason is anything other than RecordCursor.NoNextReason.SOURCE_EXHAUSTED, the returned continuation must not be an end continuation. Conversely, if the result's NoNextReason is SOURCE_EXHAUSTED, then the returned continuation must be an an "end continuation".

In either case, the returned RecordCursorContinuation can be serialized to an opaque byte array using RecordCursorContinuation.toBytes(). This can be passed back into a new cursor of the same type, with all other parameters remaining the same.

Specified by:

onNext in interface RecordCursor<U>

Returns:

a future for the next result from this cursor representing either the next record or an indication of why the cursor stopped

See Also:

RecordCursorResult, RecordCursorContinuation

onHasNext

@Nonnull
 @Deprecated
public CompletableFuture<Boolean> onHasNext()

Deprecated.

Description copied from interface: RecordCursor

Asynchronously check whether there are more records available from the cursor.

Specified by:

onHasNext in interface RecordCursor<U>

Returns:

a future that when complete will hold true if RecordCursor.next() would return a record.

See Also:

AsyncIterator.onHasNext()

next

@Nullable
 @Deprecated
public U next()

Deprecated.

Description copied from interface: RecordCursor

Return the next value.

Specified by:

next in interface RecordCursor<U>

Specified by:

next in interface Iterator<U>

Returns:

the next value

getContinuation

@Nullable
 @Deprecated
public byte[] getContinuation()

Deprecated.

Description copied from interface: RecordCursor

Get a byte string that can be used to continue a query after the last record returned.

Specified by:

getContinuation in interface RecordCursor<U>

Returns:

opaque byte array denoting where the cursor should pick up. This can be passed back into a new cursor of the same type, with all other parameters remaining the same. Returns null if the underlying source is completely exhausted, independent of any limit passed to the cursor creator. Since such creators generally accept null to mean no continuation, that is, start from the beginning, one must check for null from getContinuation to keep from starting over. Result is not always defined if called before onHasNext or before next after onHasNext has returned true. That is, a continuation is only guaranteed when called "between" records from a while (hasNext) next loop or after its end.

getNoNextReason

@Nonnull
 @Deprecated
public RecordCursor.NoNextReason getNoNextReason()

Deprecated.

Description copied from interface: RecordCursor

Get the reason that the cursor has reached the end and returned false for RecordCursor.hasNext(). If hasNext was not called or returned true last time, the result is undefined and may be an exception.

Specified by:

getNoNextReason in interface RecordCursor<U>

Returns:

the reason that the cursor stopped

close

public void close()

Specified by:

close in interface RecordCursor<U>

Specified by:

close in interface AutoCloseable

getExecutor

@Nonnull
public Executor getExecutor()

Specified by:

getExecutor in interface RecordCursor<U>

getTimer

@Nullable
public FDBStoreTimer getTimer()

Get the FDBStoreTimer used to instrument events of this cursor.

Returns:

the timer used to instrument this cursor

accept

public boolean accept(@Nonnull
                      RecordCursorVisitor visitor)

Description copied from interface: RecordCursor

Accept a visit from hierarchical visitor, which implements RecordCursorVisitor. By contract, implementations of this method must return the value of visitor.visitLeave(this), which determines whether or not subsequent siblings of this cursor should be visited.

Specified by:

accept in interface RecordCursor<U>

Parameters:

visitor - a hierarchical visitor

Returns:

true if the subsequent siblings of the cursor should be visited, and false otherwise