org.apache.hadoop.hbase.regionserver

Class SegmentScanner

java.lang.Object

org.apache.hadoop.hbase.regionserver.SegmentScanner

All Implemented Interfaces:

Closeable, AutoCloseable, KeyValueScanner, Shipper

@InterfaceAudience.Private
public class SegmentScanner
extends Object
implements KeyValueScanner

A scanner of a single memstore segment.

Field Summary

Fields

Modifier and Type	Field and Description
protected boolean	closed
protected Cell	current
private static long	DEFAULT_SCANNER_ORDER
protected Iterator<Cell>	iter
private Cell	last
private long	readPoint
private long	scannerOrder Order of this scanner relative to other scanners.
protected Segment	segment
private boolean	stopSkippingKVsIfNextRow
private Cell	stopSkippingKVsRow

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

NO_NEXT_INDEXED_KEY

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	SegmentScanner(Segment segment, long readPoint)
protected	SegmentScanner(Segment segment, long readPoint, long scannerOrder)

Method Summary

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() This function should be never called on scanners that always do real seek operations (i.e.
org.apache.hadoop.fs.Path	getFilePath()
private Cell	getHighest(Cell first, Cell second) Private internal method that returns the higher of the two key values, or null if they are both null
protected Iterator<Cell>	getIterator(Cell cell)
Cell	getNextIndexedKey()
long	getScannerOrder() Get the order of this KeyValueScanner.
private Segment	getSegment() Private Methods
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 the scanner
boolean	realSeekDone() This scanner is working solely on the in-memory MemStore and doesn't work on store files, MutableCellSetSegmentScanner always does the seek, therefore always returning true.
boolean	requestSeek(Cell c, 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 cell) Reseek the scanner at or after the specified KeyValue.
boolean	seek(Cell cell) Seek the scanner at or after the specified Cell.
boolean	seekToLastRow() Seek the scanner at the first KeyValue of last row
boolean	seekToPreviousRow(Cell cell) Seek the scanner at the first Cell of the row which is the previous row of specified key
void	shipped() Called after a batch of rows scanned (RPC) and set to be returned to client.
boolean	shouldUseScanner(Scan scan, HStore store, long oldestUnexpiredTS) This functionality should be resolved in the higher level which is MemStoreScanner, currently returns true as default.
String	toString()
protected void	updateCurrent() Private internal method for iterating over the segment, skipping the cells with irrelevant MVCC

Methods inherited from class java.lang.Object

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

Field Detail

scannerOrder

private long scannerOrder

Order of this scanner relative to other scanners. See KeyValueScanner.getScannerOrder().

DEFAULT_SCANNER_ORDER

private static final long DEFAULT_SCANNER_ORDER

See Also:

Constant Field Values

segment

protected final Segment segment

readPoint

private long readPoint

iter

protected Iterator<Cell> iter

current

protected Cell current

stopSkippingKVsIfNextRow

private boolean stopSkippingKVsIfNextRow

stopSkippingKVsRow

private Cell stopSkippingKVsRow

last

private Cell last

closed

protected boolean closed

Constructor Detail

SegmentScanner

protected SegmentScanner(Segment segment,
                         long readPoint)

SegmentScanner

protected SegmentScanner(Segment segment,
                         long readPoint,
                         long scannerOrder)

Parameters:

scannerOrder - see KeyValueScanner.getScannerOrder(). Scanners are ordered from 0 (oldest) to newest in increasing order.

Method Detail

peek

public Cell peek()

Look at the next Cell in this scanner, but do not iterate the scanner

Specified by:

peek in interface KeyValueScanner

Returns:

the currently observed Cell

next

public Cell next()
          throws IOException

Return the next Cell in this scanner, iterating the scanner

Specified by:

next in interface KeyValueScanner

Returns:

the next Cell or null if end of scanner

Throws:

IOException

seek

public boolean seek(Cell cell)
             throws IOException

Seek the scanner at or after the specified Cell.

Specified by:

seek in interface KeyValueScanner

Parameters:

cell - seek value

Returns:

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

Throws:

IOException

getIterator

protected Iterator<Cell> getIterator(Cell cell)

reseek

public boolean reseek(Cell cell)
               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.

Specified by:

reseek in interface KeyValueScanner

Parameters:

cell - seek value (should be non-null)

Returns:

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

Throws:

IOException

backwardSeek

public 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

Specified by:

backwardSeek in interface KeyValueScanner

Parameters:

key - seek Cell

Returns:

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

Throws:

IOException

seekToPreviousRow

public boolean seekToPreviousRow(Cell cell)
                          throws IOException

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

Specified by:

seekToPreviousRow in interface KeyValueScanner

Parameters:

cell - seek value

Returns:

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

Throws:

IOException

seekToLastRow

public boolean seekToLastRow()
                      throws IOException

Seek the scanner at the first KeyValue of last row

Specified by:

seekToLastRow in interface KeyValueScanner

Returns:

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

Throws:

IOException

getScannerOrder

public long getScannerOrder()

Description copied from interface: KeyValueScanner

Get the order of this KeyValueScanner. This is only relevant for StoreFileScanners and MemStoreScanners (other scanners simply return 0). This is required for comparing multiple files to find out which one has the latest data. StoreFileScanners are ordered from 0 (oldest) to newest in increasing order. MemStoreScanner gets LONG.max since it always contains freshest data.

Specified by:

getScannerOrder in interface KeyValueScanner

See Also:

KeyValueScanner.getScannerOrder()

close

public void close()

Close the KeyValue scanner.

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Specified by:

close in interface KeyValueScanner

shouldUseScanner

public boolean shouldUseScanner(Scan scan,
                                HStore store,
                                long oldestUnexpiredTS)

This functionality should be resolved in the higher level which is MemStoreScanner, currently returns true as default. Doesn't throw IllegalStateException in order not to change the signature of the overridden method

Specified by:

shouldUseScanner in interface KeyValueScanner

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

public boolean requestSeek(Cell c,
                           boolean forward,
                           boolean useBloom)
                    throws IOException

Description copied from interface: KeyValueScanner

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

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

useBloom - whether to enable multi-column Bloom filter optimization

Throws:

IOException

realSeekDone

public boolean realSeekDone()

This scanner is working solely on the in-memory MemStore and doesn't work on store files, MutableCellSetSegmentScanner always does the seek, therefore always returning true.

Specified by:

realSeekDone in interface KeyValueScanner

enforceSeek

public void enforceSeek()
                 throws IOException

This function should be never called on scanners that always do real seek operations (i.e. most of the scanners and also this one). The easiest way to achieve this is to call realSeekDone() first.

Specified by:

enforceSeek in interface KeyValueScanner

Throws:

IOException

isFileScanner

public boolean isFileScanner()

Specified by:

isFileScanner in interface KeyValueScanner

Returns:

true if this is a file scanner. Otherwise a memory scanner is assumed.

getFilePath

public org.apache.hadoop.fs.Path getFilePath()

Specified by:

getFilePath in interface KeyValueScanner

Returns:

the file path if this is a file scanner, otherwise null.

See Also:

KeyValueScanner.isFileScanner()

getNextIndexedKey

public Cell getNextIndexedKey()

Specified by:

getNextIndexedKey in interface KeyValueScanner

Returns:

the next key in the index (the key to seek to the next block) if known, or null otherwise Not relevant for in-memory scanner

shipped

public void shipped()
             throws IOException

Called after a batch of rows scanned (RPC) and set to be returned to client. Any in between cleanup can be done here. Nothing to be done for MutableCellSetSegmentScanner.

Specified by:

shipped in interface Shipper

Throws:

IOException

toString

public String toString()

Overrides:

toString in class Object

getSegment

private Segment getSegment()

Private Methods

updateCurrent

protected void updateCurrent()

Private internal method for iterating over the segment, skipping the cells with irrelevant MVCC

getHighest

private Cell getHighest(Cell first,
                        Cell second)

Private internal method that returns the higher of the two key values, or null if they are both null