org.gridgain.grid.ggfs

Class GridGgfsGroupDataBlocksKeyMapper

java.lang.Object

org.gridgain.grid.kernal.processors.cache.GridCacheDefaultAffinityKeyMapper

org.gridgain.grid.ggfs.GridGgfsGroupDataBlocksKeyMapper

All Implemented Interfaces:

Serializable, org.gridgain.grid.cache.affinity.GridCacheAffinityKeyMapper

public class GridGgfsGroupDataBlocksKeyMapper
extends org.gridgain.grid.kernal.processors.cache.GridCacheDefaultAffinityKeyMapper

GGFS class providing ability to group file's data blocks together on one node. All blocks within the same group are guaranteed to be cached together on the same node. Group size parameter controls how many sequential blocks will be cached together on the same node.

For example, if block size is 64kb and group size is 256, then each group will contain 64kb * 256 = 16Mb. Larger group sizes would reduce number of splits required to run map-reduce tasks, but will increase inequality of data size being stored on different nodes.

Note that groupSize() parameter must correlate to Hadoop split size parameter defined in Hadoop via mapred.max.split.size property. Ideally you want all blocks accessed within one split to be mapped to 1 group, so they can be located on the same grid node. For example, default Hadoop split size is 64mb and default GGFS block size is 64kb. This means that to make sure that each split goes only through blocks on the same node (without hopping between nodes over network), we have to make the groupSize() value be equal to 64mb / 64kb = 1024.

It is required for GGFS data cache to be configured with this mapper. Here is an example of how it can be specified in XML configuration:

 <bean id="cacheCfgBase" class="org.gridgain.grid.cache.GridCacheConfiguration" abstract="true">
     ...
     <property name="affinityMapper">
         <bean class="org.gridgain.grid.ggfs.GridGgfsGroupDataBlocksKeyMapper">
             <!-- How many sequential blocks will be stored on the same node. -->
             <constructor-arg value="512"/>
         </bean>
     </property>
     ...
 </bean>
 

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
GridGgfsGroupDataBlocksKeyMapper(int grpSize) Constructs affinity mapper to group several data blocks with the same key.

Method Summary

Methods

Modifier and Type	Method and Description
Object	affinityKey(Object key)
int	groupSize()
String	toString()

Methods inherited from class org.gridgain.grid.kernal.processors.cache.GridCacheDefaultAffinityKeyMapper

reset

Methods inherited from class java.lang.Object

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

Constructor Detail

GridGgfsGroupDataBlocksKeyMapper

public GridGgfsGroupDataBlocksKeyMapper(int grpSize)

Constructs affinity mapper to group several data blocks with the same key.

Parameters:

grpSize - Size of the group in blocks.

Method Detail

affinityKey

public Object affinityKey(Object key)

Specified by:

affinityKey in interface org.gridgain.grid.cache.affinity.GridCacheAffinityKeyMapper

Overrides:

affinityKey in class org.gridgain.grid.kernal.processors.cache.GridCacheDefaultAffinityKeyMapper

groupSize

public int groupSize()

Returns:

Size of the group.

toString

public String toString()

Overrides:

toString in class Object