org.apache.druid.segment

Interface RowIterator

All Superinterfaces:

AutoCloseable, Closeable, TimeAndDimsIterator

All Known Subinterfaces:

TransformableRowIterator

All Known Implementing Classes:

ForwardingRowIterator

public interface RowIterator
extends TimeAndDimsIterator

Extension of TimeAndDimsIterator, specialized for RowPointer instead of TimeAndDimsPointer. Also, RowIterator encapsulates tracking of data point changes between TimeAndDimsIterator.moveToNext() calls via mark() and hasTimeAndDimsChangedSinceMark() methods. This functionality is used in RowCombiningTimeAndDimsIterator, and also internally in MergingRowIterator to reduce the number of comparisons that this class makes. This functionality is added directly to RowIterator interface rather than left to be implemented externally to this interface, because it's inefficient to do the latter with "generic" RowIterator, because of TimeAndDimsPointer allocation-free design, that reuses objects. On the other hand, some implementations of RowIterator allow to optimize mark() and hasTimeAndDimsChangedSinceMark().

Method Summary

Modifier and Type	Method and Description
RowPointer	getPointer() Returns a pointer to the current row.
boolean	hasTimeAndDimsChangedSinceMark() Compares the "memoized" data point from the last mark() call with the data point, to which getPointer() currently points.
void	mark() "Memoizes" the data point, to which getPointer() currently points.

Methods inherited from interface org.apache.druid.segment.TimeAndDimsIterator

close, moveToNext

Method Detail

mark

void mark()

"Memoizes" the data point, to which getPointer() currently points. If the last call to TimeAndDimsIterator.moveToNext() returned false, the behaviour of this method is undefined, e. g. it may throw a runtime exception.

hasTimeAndDimsChangedSinceMark

boolean hasTimeAndDimsChangedSinceMark()

Compares the "memoized" data point from the last mark() call with the data point, to which getPointer() currently points. Comparison is made in terms of TimeAndDimsPointer.compareTo(org.apache.druid.segment.TimeAndDimsPointer) contract. If mark() has never been called, or the last call to TimeAndDimsIterator.moveToNext() returned false, the behaviour of this method is undefined: it may arbitrarily return true, or false, or throw a runtime exception.

getPointer

RowPointer getPointer()

Returns a pointer to the current row. This method may return the same (in terms of referencial identity), as well as different object on any calls, but the row itself, to which the returned object points, changes after each TimeAndDimsIterator.moveToNext() call that returns true. This method must not be called before ever calling to TimeAndDimsIterator.moveToNext(). If the very first call to TimeAndDimsIterator.moveToNext() returned false, the behaviour of this method is undefined (it may return a "wrong" pointer, null, throw an exception, etc.). If TimeAndDimsIterator.moveToNext() returned true one or more times, and then eventually returned false, calling getPointer() after that should return a pointer pointing to the last valid row, as if getPointer() was called before the last (unsuccessful) call to TimeAndDimsIterator.moveToNext(). In other words, unsuccessful TimeAndDimsIterator.moveToNext() call doesn't "corrupt" the pointer. This property is used in RowCombiningTimeAndDimsIterator.moveToNext().

Specified by:

getPointer in interface TimeAndDimsIterator