KeyValueScanner (Apache HBase 1.2.12 API)

All Known Implementing Classes:

CollectionBackedScanner, DefaultMemStore.MemStoreScanner, KeyValueHeap, NonLazyKeyValueScanner, NonReversedNonLazyKeyValueScanner, ReversedKeyValueHeap, ReversedStoreScanner, StoreFileScanner, StoreScanner
```
@InterfaceAudience.Private
public interface KeyValueScanner
```
Scanner that returns the next KeyValue.

Field Summary

Fields
Modifier and Type	Field and Description
`static Cell`	`NO_NEXT_INDEXED_KEY` The byte array represents for NO_NEXT_INDEXED_KEY; The actual value is irrelevant because this is always compared by reference.

Method Summary

Methods
Modifier and Type	Method and Description
`boolean`	`backwardSeek(Cell key)` 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
`void`	`close()` Close the KeyValue scanner.
`void`	`enforceSeek()` Does the real seek operation in case it was skipped by seekToRowCol(KeyValue, boolean) (TODO: Whats this?).
`Cell`	`getNextIndexedKey()`
`long`	`getSequenceID()` Get the sequence id associated with this KeyValueScanner.
`boolean`	`isFileScanner()`
`Cell`	`next()` Return the next Cell in this scanner, iterating the scanner
`Cell`	`peek()` Look at the next Cell in this scanner, but do not iterate scanner.
`boolean`	`realSeekDone()` We optimize our store scanners by checking the most recent store file first, so we sometimes pretend we have done a seek but delay it until the store scanner bubbles up to the top of the key-value heap.
`boolean`	`requestSeek(Cell kv, boolean forward, boolean useBloom)` Similar to `seek(org.apache.hadoop.hbase.Cell)` (or `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 key)` Reseek the scanner at or after the specified KeyValue.
`boolean`	`seek(Cell key)` Seek the scanner at or after the specified KeyValue.
`boolean`	`seekToLastRow()` Seek the scanner at the first KeyValue of last row
`boolean`	`seekToPreviousRow(Cell key)` Seek the scanner at the first Cell of the row which is the previous row of specified key
`boolean`	`shouldUseScanner(Scan scan, Store store, long oldestUnexpiredTS)` Allows to filter out scanners (both StoreFile and memstore) that we don't want to use based on criteria such as Bloom filters and timestamp ranges.

- Field Detail
  - NO_NEXT_INDEXED_KEY
```
static final Cell NO_NEXT_INDEXED_KEY
```
    The byte array represents for NO_NEXT_INDEXED_KEY; The actual value is irrelevant because this is always compared by reference.
- Method Detail
  - peek
```
Cell peek()
```
    Look at the next Cell in this scanner, but do not iterate scanner.
    
    Returns:
    the next Cell
  - next
```
Cell next()
          throws IOException
```
    Return the next Cell in this scanner, iterating the scanner
    
    Returns:
    the next Cell
    
    Throws:
    
    IOException
  - seek
```
boolean seek(Cell key)
             throws IOException
```
    Seek the scanner at or after the specified KeyValue.
    
    Parameters:
    key - seek value
    
    Returns:
    true if scanner has values left, false if end of scanner
    
    Throws:
    
    IOException
  - reseek
```
boolean reseek(Cell key)
               throws IOException
```
    Reseek the scanner at or after the specified KeyValue. This method is guaranteed to seek at or after the required key only if the key comes after the current position of the scanner. Should not be used to seek to a key which may come before the current position.
    
    Parameters:
    key - seek value (should be non-null)
    
    Returns:
    true if scanner has values left, false if end of scanner
    
    Throws:
    
    IOException
  - getSequenceID
```
long getSequenceID()
```
    Get the sequence id associated with this KeyValueScanner. This is required for comparing multiple files to find out which one has the latest data. The default implementation for this would be to return 0. A file having lower sequence id will be considered to be the older one.
  - close
```
void close()
```
    Close the KeyValue scanner.
  - shouldUseScanner
```
boolean shouldUseScanner(Scan scan,
                       Store store,
                       long oldestUnexpiredTS)
```
    Allows to filter out scanners (both StoreFile and memstore) that we don't want to use based on criteria such as Bloom filters and timestamp ranges.
    
    Parameters:
    scan - the scan that we are selecting scanners for
    store - the store we are performing the scan on.
    oldestUnexpiredTS - the oldest timestamp we are interested in for this query, based on TTL
    
    Returns:
    true if the scanner should be included in the query
  - requestSeek
```
boolean requestSeek(Cell kv,
                  boolean forward,
                  boolean useBloom)
                    throws IOException
```
    Similar to seek(org.apache.hadoop.hbase.Cell) (or 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.
    
    Parameters:
    forward - do a forward-only "reseek" instead of a random-access seek
    useBloom - whether to enable multi-column Bloom filter optimization
    
    Throws:
    
    IOException
  - realSeekDone
```
boolean realSeekDone()
```
    We optimize our store scanners by checking the most recent store file first, so we sometimes pretend we have done a seek but delay it until the store scanner bubbles up to the top of the key-value heap. This method is then used to ensure the top store file scanner has done a seek operation.
  - enforceSeek
```
void enforceSeek()
                 throws IOException
```
    Does the real seek operation in case it was skipped by seekToRowCol(KeyValue, boolean) (TODO: Whats this?). Note that this function should be never called on scanners that always do real seek operations (i.e. most of the scanners). The easiest way to achieve this is to call realSeekDone() first.
    
    Throws:
    
    IOException
  - isFileScanner
```
boolean isFileScanner()
```
    Returns:
    true if this is a file scanner. Otherwise a memory scanner is assumed.
  - backwardSeek
```
boolean backwardSeek(Cell key)
                     throws IOException
```
    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
    
    Parameters:
    key - seek KeyValue
    
    Returns:
    true if the scanner is at the valid KeyValue, false if such KeyValue does not exist
    
    Throws:
    
    IOException
  - seekToPreviousRow
```
boolean seekToPreviousRow(Cell key)
                          throws IOException
```
    Seek the scanner at the first Cell of the row which is the previous row of specified key
    
    Parameters:
    key - seek value
    
    Returns:
    true if the scanner at the first valid Cell of previous row, false if not existing such Cell
    
    Throws:
    
    IOException
  - seekToLastRow
```
boolean seekToLastRow()
                      throws IOException
```
    Seek the scanner at the first KeyValue of last row
    
    Returns:
    true if scanner has values left, false if the underlying data is empty
    
    Throws:
    
    IOException
  - getNextIndexedKey
```
Cell getNextIndexedKey()
```
    Returns:
    the next key in the index (the key to seek to the next block) if known, or null otherwise

Interface KeyValueScanner

Field Summary

Method Summary

Field Detail

NO_NEXT_INDEXED_KEY

Method Detail

peek

next

seek

reseek

getSequenceID

close

shouldUseScanner

requestSeek

realSeekDone

enforceSeek

isFileScanner

backwardSeek

seekToPreviousRow

seekToLastRow

getNextIndexedKey