org.apache.hadoop.hbase.regionserver

Class ReversedKeyValueHeap

java.lang.Object

org.apache.hadoop.hbase.regionserver.NonLazyKeyValueScanner

org.apache.hadoop.hbase.regionserver.NonReversedNonLazyKeyValueScanner

org.apache.hadoop.hbase.regionserver.KeyValueHeap

org.apache.hadoop.hbase.regionserver.ReversedKeyValueHeap

All Implemented Interfaces:

Closeable, AutoCloseable, InternalScanner, KeyValueScanner

@InterfaceAudience.Private
public class ReversedKeyValueHeap
extends KeyValueHeap

ReversedKeyValueHeap is used for supporting reversed scanning. Compared with KeyValueHeap, its scanner comparator is a little different (see ReversedKVScannerComparator), all seek is backward seek(see KeyValueScanner.backwardSeek(org.apache.hadoop.hbase.KeyValue)), and it will jump to the previous row if it is already at the end of one row when calling next().

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.hadoop.hbase.regionserver.KeyValueHeap

KeyValueHeap.KVScannerComparator

Field Summary

Fields inherited from class org.apache.hadoop.hbase.regionserver.KeyValueHeap

comparator, current, heap

Constructor Summary

Constructors

Constructor and Description
ReversedKeyValueHeap(List<? extends KeyValueScanner> scanners, KeyValue.KVComparator comparator)

Method Summary

Methods

Modifier and Type	Method and Description
boolean	backwardSeek(KeyValue seekKey) Seek the scanner at or before the row of specified KeyValue, it firstly tries to seek the scanner at or after the specified KeyValue, return if peek KeyValue of scanner has the same row with specified KeyValue, otherwise seek the scanner at the first KeyValue of the row which is the previous row of specified KeyValue
KeyValue	next() Return the next KeyValue in this scanner, iterating the scanner
boolean	requestSeek(KeyValue key, boolean forward, boolean useBloom) Similar to KeyValueScanner.seek(org.apache.hadoop.hbase.KeyValue) (or KeyValueScanner.reseek(org.apache.hadoop.hbase.KeyValue) if forward is true) but only does a seek operation after checking that it is really necessary for the row/column combination specified by the kv parameter.
boolean	reseek(KeyValue seekKey) This function is identical to the KeyValueHeap.seek(KeyValue) function except that scanner.seek(seekKey) is changed to scanner.reseek(seekKey).
boolean	seek(KeyValue seekKey) Seeks all scanners at or below the specified seek key.
boolean	seekToLastRow() Seek the scanner at the first KeyValue of last row
boolean	seekToPreviousRow(KeyValue seekKey) Seek the scanner at the first KeyValue of the row which is the previous row of specified key

Methods inherited from class org.apache.hadoop.hbase.regionserver.KeyValueHeap

close, getHeap, getSequenceID, next, next, peek, pollRealKV

Methods inherited from class org.apache.hadoop.hbase.regionserver.NonLazyKeyValueScanner

doRealSeek, enforceSeek, isFileScanner, realSeekDone, shouldUseScanner

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.hadoop.hbase.regionserver.KeyValueScanner

enforceSeek, isFileScanner, realSeekDone, shouldUseScanner

Constructor Detail

ReversedKeyValueHeap

public ReversedKeyValueHeap(List<? extends KeyValueScanner> scanners,
                    KeyValue.KVComparator comparator)
                     throws IOException

Parameters:

scanners -

comparator -

Throws:

IOException

Method Detail

seek

public boolean seek(KeyValue seekKey)
             throws IOException

Description copied from class: KeyValueHeap

Seeks all scanners at or below the specified seek key. If we earlied-out of a row, we may end up skipping values that were never reached yet. Rather than iterating down, we want to give the opportunity to re-seek.

As individual scanners may run past their ends, those scanners are automatically closed and removed from the heap.

This function (and KeyValueHeap.reseek(KeyValue)) does not do multi-column Bloom filter and lazy-seek optimizations. To enable those, call KeyValueHeap.requestSeek(KeyValue, boolean, boolean).

Specified by:

seek in interface KeyValueScanner

Overrides:

seek in class KeyValueHeap

Parameters:

seekKey - KeyValue to seek at or after

Returns:

true if KeyValues exist at or after specified key, false if not

Throws:

IOException

reseek

public boolean reseek(KeyValue seekKey)
               throws IOException

Description copied from class: KeyValueHeap

This function is identical to the KeyValueHeap.seek(KeyValue) function except that scanner.seek(seekKey) is changed to scanner.reseek(seekKey).

Specified by:

reseek in interface KeyValueScanner

Overrides:

reseek in class KeyValueHeap

Parameters:

seekKey - seek value (should be non-null)

Returns:

true if scanner has values left, false if end of scanner

Throws:

IOException

requestSeek

public boolean requestSeek(KeyValue key,
                  boolean forward,
                  boolean useBloom)
                    throws IOException

Description copied from class: KeyValueHeap

Similar to KeyValueScanner.seek(org.apache.hadoop.hbase.KeyValue) (or KeyValueScanner.reseek(org.apache.hadoop.hbase.KeyValue) if forward is true) but only does a seek operation after checking that it is really necessary for the row/column combination specified by the kv parameter. This function was added to avoid unnecessary disk seeks by checking row-column Bloom filters before a seek on multi-column get/scan queries, and to optimize by looking up more recent files first.

Specified by:

requestSeek in interface KeyValueScanner

Overrides:

requestSeek in class KeyValueHeap

forward - do a forward-only "reseek" instead of a random-access seek

useBloom - whether to enable multi-column Bloom filter optimization

Throws:

IOException

seekToPreviousRow

public boolean seekToPreviousRow(KeyValue seekKey)
                          throws IOException

Description copied from interface: KeyValueScanner

Seek the scanner at the first KeyValue of the row which is the previous row of specified key

Specified by:

seekToPreviousRow in interface KeyValueScanner

Overrides:

seekToPreviousRow in class NonReversedNonLazyKeyValueScanner

Parameters:

seekKey - seek value

Returns:

true if the scanner at the first valid KeyValue of previous row, false if not existing such KeyValue

Throws:

IOException

backwardSeek

public boolean backwardSeek(KeyValue seekKey)
                     throws IOException

Description copied from interface: KeyValueScanner

Seek the scanner at or before the row of specified KeyValue, it firstly tries to seek the scanner at or after the specified KeyValue, return if peek KeyValue of scanner has the same row with specified KeyValue, otherwise seek the scanner at the first KeyValue of the row which is the previous row of specified KeyValue

Specified by:

backwardSeek in interface KeyValueScanner

Overrides:

backwardSeek in class NonReversedNonLazyKeyValueScanner

Parameters:

seekKey - seek KeyValue

Returns:

true if the scanner is at the valid KeyValue, false if such KeyValue does not exist

Throws:

IOException

next

public KeyValue next()
              throws IOException

Description copied from interface: KeyValueScanner

Return the next KeyValue in this scanner, iterating the scanner

Specified by:

next in interface KeyValueScanner

Overrides:

next in class KeyValueHeap

Returns:

the next KeyValue

Throws:

IOException

seekToLastRow

public boolean seekToLastRow()
                      throws IOException

Description copied from interface: KeyValueScanner

Seek the scanner at the first KeyValue of last row

Specified by:

seekToLastRow in interface KeyValueScanner

Overrides:

seekToLastRow in class NonReversedNonLazyKeyValueScanner

Returns:

true if scanner has values left, false if the underlying data is empty

Throws:

IOException