org.apache.hadoop.hbase.filter
Class FirstKeyOnlyFilter

java.lang.Object
  org.apache.hadoop.hbase.filter.FirstKeyOnlyFilter

All Implemented Interfaces:

Filter, org.apache.hadoop.io.Writable

public class FirstKeyOnlyFilter
extends Object
implements Filter

A filter that will only return the first KV from each row.

This filter can be used to more efficiently perform row count operations.

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.hadoop.hbase.filter.Filter

Filter.ReturnCode

Constructor Summary

FirstKeyOnlyFilter()

Method Summary

boolean	filterAllRemaining() If this returns true, the scan will terminate.
Filter.ReturnCode	filterKeyValue(KeyValue v) A way to filter based on the column family, column qualifier and/or the column value.
boolean	filterRow() Last chance to veto row based on previous Filter.filterKeyValue(KeyValue) calls.
boolean	filterRowKey(byte[] buffer, int offset, int length) Filters a row based on the row key.
void	readFields(DataInput in)
void	reset() Reset the state of the filter between rows.
void	write(DataOutput out)

Methods inherited from class java.lang.Object

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

Constructor Detail

FirstKeyOnlyFilter

public FirstKeyOnlyFilter()

Method Detail

reset

public void reset()

Description copied from interface: Filter

Reset the state of the filter between rows.

Specified by:

reset in interface Filter

filterRowKey

public boolean filterRowKey(byte[] buffer,
                            int offset,
                            int length)

Description copied from interface: Filter

Filters a row based on the row key. If this returns true, the entire row will be excluded. If false, each KeyValue in the row will be passed to Filter.filterKeyValue(KeyValue) below.

Specified by:

filterRowKey in interface Filter

Parameters:

buffer - buffer containing row key

offset - offset into buffer where row key starts

length - length of the row key

Returns:

true, remove entire row, false, include the row (maybe).

filterAllRemaining

public boolean filterAllRemaining()

Description copied from interface: Filter

If this returns true, the scan will terminate.

Specified by:

filterAllRemaining in interface Filter

Returns:

true to end scan, false to continue.

filterKeyValue

public Filter.ReturnCode filterKeyValue(KeyValue v)

Description copied from interface: Filter

A way to filter based on the column family, column qualifier and/or the column value. Return code is described below. This allows filters to filter only certain number of columns, then terminate without matching ever column. If your filter returns ReturnCode.NEXT_ROW, it should return ReturnCode.NEXT_ROW until Filter.reset() is called just in case the caller calls for the next row.

Specified by:

filterKeyValue in interface Filter

Parameters:

v - the KeyValue in question

Returns:

code as described below

See Also:

Filter.ReturnCode

filterRow

public boolean filterRow()

Description copied from interface: Filter

Last chance to veto row based on previous Filter.filterKeyValue(KeyValue) calls. The filter needs to retain state then return a particular value for this call if they wish to exclude a row if a certain column is missing (for example).

Specified by:

filterRow in interface Filter

Returns:

true to exclude row, false to include row.

write

public void write(DataOutput out)
           throws IOException

Specified by:

write in interface org.apache.hadoop.io.Writable

Throws:

IOException

readFields

public void readFields(DataInput in)
                throws IOException

Specified by:

readFields in interface org.apache.hadoop.io.Writable

Throws:

IOException