ReversedKeyValueHeap (Apache HBase 1.4.11 API)

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.Cell)), 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
- Fields inherited from interface org.apache.hadoop.hbase.regionserver.KeyValueScanner
  NO_NEXT_INDEXED_KEY

Constructor Summary

Constructors
Constructor and Description

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

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

Method Summary

Methods
Modifier and Type	Method and Description
`boolean`	`backwardSeek(Cell seekKey)` Seek the scanner at or before the row of specified Cell, it firstly tries to seek the scanner at or after the specified Cell, return if peek KeyValue of scanner has the same row with specified Cell, otherwise seek the scanner at the first Cell of the row which is the previous row of specified KeyValue
`Cell`	`next()` Return the next Cell in this scanner, iterating the scanner
`boolean`	`requestSeek(Cell key, boolean forward, boolean useBloom)` Similar to `KeyValueScanner.seek(org.apache.hadoop.hbase.Cell)` (or `KeyValueScanner.reseek(org.apache.hadoop.hbase.Cell)` 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(Cell seekKey)` This function is identical to the `KeyValueHeap.seek(Cell)` function except that scanner.seek(seekKey) is changed to scanner.reseek(seekKey).
`boolean`	`seek(Cell 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(Cell seekKey)` Seek the scanner at the first Cell of the row which is the previous row of specified key

Methods inherited from class org.apache.hadoop.hbase.regionserver.KeyValueHeap
close, getHeap, getNextIndexedKey, getScannerOrder, 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(Cell 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(Cell)) does not do multi-column Bloom filter and lazy-seek optimizations. To enable those, call KeyValueHeap.requestSeek(Cell, 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(Cell seekKey)
               throws IOException
```
    Description copied from class: KeyValueHeap
    
    This function is identical to the KeyValueHeap.seek(Cell) 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(Cell key,
                  boolean forward,
                  boolean useBloom)
                    throws IOException
```
    Description copied from class: KeyValueHeap
    
    Similar to KeyValueScanner.seek(org.apache.hadoop.hbase.Cell) (or KeyValueScanner.reseek(org.apache.hadoop.hbase.Cell) 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(Cell seekKey)
                          throws IOException
```
    Description copied from interface: KeyValueScanner
    
    Seek the scanner at the first Cell 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 Cell of previous row, false if not existing such Cell
    
    Throws:
    
    IOException
  - backwardSeek
```
public boolean backwardSeek(Cell seekKey)
                     throws IOException
```
    Description copied from interface: KeyValueScanner
    
    Seek the scanner at or before the row of specified Cell, it firstly tries to seek the scanner at or after the specified Cell, return if peek KeyValue of scanner has the same row with specified Cell, otherwise seek the scanner at the first Cell 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 Cell next()
          throws IOException
```
    Description copied from interface: KeyValueScanner
    
    Return the next Cell in this scanner, iterating the scanner
    
    Specified by:
    
    next in interface KeyValueScanner
    
    Overrides:
    
    next in class KeyValueHeap
    
    Returns:
    the next Cell
    
    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

Class ReversedKeyValueHeap

Nested Class Summary

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

Field Summary

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

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

Constructor Summary

Method Summary

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

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

Methods inherited from class java.lang.Object

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

Constructor Detail

ReversedKeyValueHeap

Method Detail

seek

reseek

requestSeek

seekToPreviousRow

backwardSeek

next

seekToLastRow