org.apache.hadoop.hbase.regionserver

Interface RegionScanner

All Superinterfaces:

AutoCloseable, Closeable, InternalScanner

@InterfaceAudience.LimitedPrivate(value="Coprocesssor")
@InterfaceStability.Evolving
public interface RegionScanner
extends InternalScanner

RegionScanner describes iterators over rows in an HRegion.

Method Summary

Methods

Modifier and Type	Method and Description
int	getBatch()
long	getMaxResultSize()
long	getMvccReadPoint()
HRegionInfo	getRegionInfo()
boolean	isFilterDone()
boolean	nextRaw(List<Cell> result) Grab the next row's worth of values.
boolean	nextRaw(List<Cell> result, ScannerContext scannerContext) Grab the next row's worth of values.
boolean	reseek(byte[] row) Do a reseek to the required row.

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

close, next, next

Method Detail

getRegionInfo

HRegionInfo getRegionInfo()

Returns:

The RegionInfo for this scanner.

isFilterDone

boolean isFilterDone()
                     throws IOException

Returns:

True if a filter indicates that this scanner will return no further rows.

Throws:

IOException - in case of I/O failure on a filter.

reseek

boolean reseek(byte[] row)
               throws IOException

Do a reseek to the required row. Should not be used to seek to a key which may come before the current position. Always seeks to the beginning of a row boundary.

Throws:

IOException

IllegalArgumentException - if row is null

getMaxResultSize

long getMaxResultSize()

Returns:

The preferred max buffersize. See Scan.setMaxResultSize(long)

getMvccReadPoint

long getMvccReadPoint()

Returns:

The Scanner's MVCC readPt see MultiVersionConsistencyControl

getBatch

int getBatch()

Returns:

The limit on the number of cells to retrieve on each call to next(). See Scan.setBatch(int)

nextRaw

boolean nextRaw(List<Cell> result)
                throws IOException

Grab the next row's worth of values. This is a special internal method to be called from coprocessor hooks to avoid expensive setup. Caller must set the thread's readpoint, start and close a region operation, an synchronize on the scanner object. Caller should maintain and update metrics. See nextRaw(List, ScannerContext)

Parameters:

result - return output array

Returns:

true if more rows exist after this one, false if scanner is done

Throws:

IOException - e

nextRaw

boolean nextRaw(List<Cell> result,
              ScannerContext scannerContext)
                throws IOException

Grab the next row's worth of values. The ScannerContext is used to enforce and track any limits associated with this call. Any progress that exists in the ScannerContext prior to calling this method will be LOST if ScannerContext.getKeepProgress() is false. Upon returning from this method, the ScannerContext will contain information about the progress made towards the limits. This is a special internal method to be called from coprocessor hooks to avoid expensive setup. Caller must set the thread's readpoint, start and close a region operation, an synchronize on the scanner object. Example:

 HRegion region = ...;
 RegionScanner scanner = ...
 MultiVersionConsistencyControl.setThreadReadPoint(scanner.getMvccReadPoint());
 region.startRegionOperation();
 try {
   synchronized(scanner) {
     ...
     boolean moreRows = scanner.nextRaw(values);
     ...
   }
 } finally {
   region.closeRegionOperation();
 }
 

Parameters:

result - return output array

scannerContext - The ScannerContext instance encapsulating all limits that should be tracked during calls to this method. The progress towards these limits can be tracked within this instance.

Returns:

true if more rows exist after this one, false if scanner is done

Throws:

IOException - e