DSO Locality API

Introduction

Working with clustered data can present additional challenges to applications which must manage this data across a series of application servers. Using the data locality methods available through the Terracotta Distributed Shared Objects (DSO) API's DsoCluster interface, you can meet these challenges by adding locality awareness to your application code. Adding locality awareness, or visibility, provides a number of advantages, including:

• Making applications more efficient with respect to data location by allowing code to be optimized along locality of reference.
• Exposing data access and usage patterns from within an application.
• Facilitating data commitment and eviction operations by providing information on the real-time location of clustered data or its absence.
• Allowing a cache to send work to the appropriate node by providing the location of data that requires processing.
• Providing insight into the effectiveness of data partitioning techniques by verifying the distribution of clustered data.

For more information on data structures, see the Terracotta DSO Data Structures Guide.

Usage

Classes that are injected with cluster awareness can call data locality methods.

The following code example shows the cluster-aware class ClusterAwareClass with a member, localityAwareFoo(), that calls the data locality method getNodesWithObjects():

See Terracotta DSO Cluster Events for more information on injecting cluster awareness into application classes.

The Methods

The data-locality methods available are:

Note the following characteristics for these methods:

• None returns null, making null checks unnecessary. In cases where there is no data to return, an empty Set or Map of empty Sets is returned (depending on the method's return type).
• An UnclusteredObjectException is thrown if any of the objects or a Map passed to one of these methods is not clustered.
• The "nodes" targeted by these methods refer to Terracotta nodes (application nodes with Terracotta running). Terracotta server instances are not subject data-locality checks.
• The values in the Sets or Maps of Sets returned by these methods are DsoNode instances. Each DsoNode instance is uniquely associated with a node and can identify that node by node ID, IP address, and hostname.

getNodesWithObject(Object object)

Use getNodesWithObject(Object object) to find which nodes contain the specified object in memory. This method has the following format:

For example, getNodesWithObject(myObject) returns a Set containing the nodes which have myObject in memory. If myObject is not resident in any node's memory, an empty Set is returned. If myObject is not clustered, an UnclusteredObjectException is thrown.

getNodesWithObjects(Object objects ... )

Use getNodesWithObjects(Object objects ... ) to find which nodes contain the specified objects in memory. This method has the following format:

For example, getNodesWithObject(myObject1, myObject2, myObject3) returns a Map with each key being one of the specified objects (myObject1, myObject2, or myObject3) and each value being a Set of nodes which have that object in memory. If an object is not resident in any node's memory, its corresponding value is an empty Set. If any of the objects specified is not clustered, an UnclusteredObjectException is thrown.

getNodesWithObjects(Collection objects)

Use getNodesWithObjects(Collection objects) to find which nodes contain the objects from the specified Collection in memory. This method has the following format:

For example, getNodesWithObjects(myObjects) returns a Map with each key being an object from the Collection myObjects and each value being a Set of nodes which have that object in memory. If an object is not resident in any node's memory, its corresponding value is an empty Set. If any of the objects in myObjects is not clustered, an UnclusteredObjectException is thrown.

getKeysForOrphanedValues(Map map)

Use getKeysForOrphanedValues(Map map) to generate a Set of keys for Map values (objects) that are not resident in the memory of any nodes. The map passed to getKeysForOrphanedValues(Map map) must be clustered and support partial loading. This method has the following format:

For example, getKeysForOrphanedValues(myMap) returns a Set of keys from myMap for any objects not found in memory on any node. If myMap is not clustered, an UnclusteredObjectException is thrown.

getKeysForLocalValues(Map map)

Use getKeysForLocalValues(Map map) to generate a Set of keys for Map values (objects) that are resident in the memory of the local node. The map passed to getKeysForLocalValues(Map map) must be clustered and support partial loading. This method has the following format:

For example, getKeysForLocalValues(myMap) returns a Set of keys from myMap for any objects found in the memory of the local node. If no objects from myMap are found, an empty Set is returned. If myMap is not clustered, an UnclusteredObjectException is thrown.