Package org.apache.hadoop.hbase.regionserver.querymatcher

Interface ColumnTracker

All Superinterfaces:

ShipperListener

All Known Implementing Classes:

ExplicitColumnTracker, NewVersionBehaviorTracker, ScanWildcardColumnTracker, VisibilityNewVersionBehaivorTracker

@Private
public interface ColumnTracker
extends ShipperListener

Implementing classes of this interface will be used for the tracking and enforcement of columns and numbers of versions and timeToLive during the course of a Get or Scan operation.

Currently there are two different types of Store/Family-level queries.

• ExplicitColumnTracker is used when the query specifies one or more column qualifiers to return in the family.
• ScanWildcardColumnTracker is used when no columns are explicitly specified.

This class is utilized by ScanQueryMatcher mainly through two methods:

• checkColumn(org.apache.hadoop.hbase.Cell, byte) is called when a Put satisfies all other conditions of the query.
• getNextRowOrNextColumn(org.apache.hadoop.hbase.Cell) is called whenever ScanQueryMatcher believes that the current column should be skipped (by timestamp, filter etc.)

These two methods returns a ScanQueryMatcher.MatchCode to define what action should be taken.

This class is NOT thread-safe as queries are never multi-threaded

Method Summary

Modifier and Type	Method	Description
ScanQueryMatcher.MatchCode	checkColumn(Cell cell, byte type)	Checks if the column is present in the list of requested columns by returning the match code instance.
ScanQueryMatcher.MatchCode	checkVersions(Cell cell, long timestamp, byte type, boolean ignoreCount)	Keeps track of the number of versions for the columns asked for.
boolean	done()	Returns true when done.
default void	doneWithColumn(Cell cell)	This method is used to inform the column tracker that we are done with this column.
ColumnCount	getColumnHint()	Used by matcher and scan/get to get a hint of the next column to seek to after checkColumn() returns SKIP.
ScanQueryMatcher.MatchCode	getNextRowOrNextColumn(Cell cell)	Retrieve the MatchCode for the next row or column
boolean	isDone(long timestamp)	Give the tracker a chance to declare it's done based on only the timestamp to allow an early out.
void	reset()	Resets the Matcher

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

beforeShipped

Method Details

checkColumn

ScanQueryMatcher.MatchCode checkColumn(Cell cell,
 byte type)
                                throws IOException

Checks if the column is present in the list of requested columns by returning the match code instance. It does not check against the number of versions for the columns asked for. To do the version check, one has to call checkVersions(Cell, long, byte, boolean) method based on the return type (INCLUDE) of this method. The values that can be returned by this method are ScanQueryMatcher.MatchCode.INCLUDE, ScanQueryMatcher.MatchCode.SEEK_NEXT_COL and ScanQueryMatcher.MatchCode.SEEK_NEXT_ROW.

Parameters:

cell - a cell with the column to match against

type - The type of the Cell

Returns:

The match code instance.

Throws:

IOException - in case there is an internal consistency problem caused by a data corruption.

checkVersions

ScanQueryMatcher.MatchCode checkVersions(Cell cell,
 long timestamp,
 byte type,
 boolean ignoreCount)
                                  throws IOException

Keeps track of the number of versions for the columns asked for. It assumes that the user has already checked if the cell needs to be included by calling the checkColumn(Cell, byte) method. The enum values returned by this method are ScanQueryMatcher.MatchCode.SKIP, ScanQueryMatcher.MatchCode.INCLUDE, ScanQueryMatcher.MatchCode.INCLUDE_AND_SEEK_NEXT_COL and ScanQueryMatcher.MatchCode.INCLUDE_AND_SEEK_NEXT_ROW. Implementations which include all the columns could just return ScanQueryMatcher.MatchCode.INCLUDE in the checkColumn(Cell, byte) method and perform all the operations in this checkVersions method.

Parameters:

cell - a cell with the column to match against

timestamp - The timestamp of the cell.

type - the type of the key value (Put/Delete)

ignoreCount - indicates if the KV needs to be excluded while counting (used during compactions. We only count KV's that are older than all the scanners' read points.)

Returns:

the scan query matcher match code instance

Throws:

IOException - in case there is an internal consistency problem caused by a data corruption.

reset

void reset()

Resets the Matcher

done

boolean done()

Returns true when done.

getColumnHint

ColumnCount getColumnHint()

Used by matcher and scan/get to get a hint of the next column to seek to after checkColumn() returns SKIP. Returns the next interesting column we want, or NULL there is none (wildcard scanner). Implementations aren't required to return anything useful unless the most recent call was to checkColumn() and the return code was SKIP. This is pretty implementation detail-y, but optimizations are like that.

Returns:

null, or a ColumnCount that we should seek to

getNextRowOrNextColumn

ScanQueryMatcher.MatchCode getNextRowOrNextColumn(Cell cell)

Retrieve the MatchCode for the next row or column

isDone

boolean isDone(long timestamp)

Give the tracker a chance to declare it's done based on only the timestamp to allow an early out.

Returns:

true to early out based on timestamp.

doneWithColumn

default void doneWithColumn(Cell cell)

This method is used to inform the column tracker that we are done with this column. We may get this information from external filters or timestamp range and we then need to indicate this information to tracker. It is currently implemented for ExplicitColumnTracker.