org.apache.hadoop.hbase.regionserver

Interface KeyValueScanner

All Known Implementing Classes:

CollectionBackedScanner, DefaultMemStore.MemStoreScanner, KeyValueHeap, NonLazyKeyValueScanner, NonReversedNonLazyKeyValueScanner, ReversedKeyValueHeap, StoreFileScanner, StoreScanner

@InterfaceAudience.Private
public interface KeyValueScanner

Scanner that returns the next KeyValue.

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, SortedSet<byte[]> columns, 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.

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,
                       SortedSet<byte[]> columns,
                       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

columns - the set of columns in the current column family, or null if not specified by the scan

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