Program guide > Access data with client applications

Use Sessions to access data in the grid

Applications can begin and end transactions through the Session interface. The Session interface also provides access to the application-based ObjectMap and JavaMap interfaces.

Each ObjectMap or JavaMap instance is directly tied to a specific Session object. Each thread that wants access to an eXtreme Scale must first obtain a Session from the ObjectGrid object. A Session instance cannot be shared concurrently between threads. WebSphere eXtreme Scale does not use any thread local storage, but platform restrictions might limit the opportunity to pass a Session from one thread to another.


The following methods are available with the Session interface. See the API documentation for more information about the following methods:

public interface Session {
    ObjectMap getMap(String cacheName) throws UndefinedMapException;

    void begin() throws TransactionAlreadyActiveException, TransactionException;

    void beginNoWriteThrough() throws TransactionAlreadyActiveException,

    public void commit() throws NoActiveTransactionException, TransactionException;

    public void rollback() throws NoActiveTransactionException, TransactionException;

    public void flush()    throws TransactionException;

    TxID getTxID() throws NoActiveTransactionException;

    boolean isWriteThroughEnabled();

    void setTransactionType(String tranType);

    public void processLogSequence(LogSequence logSequence) throws
            NoActiveTransactionException, UndefinedMapException, ObjectGridException;

    ObjectGrid getObjectGrid();

    public void setTransactionTimeout(int timeout);
    public int getTransactionTimeout();
    public boolean transactionTimedOut();

    public boolean isCommitting();
    public boolean isFlushing();

    public void markRollbackOnly(Throwable t) throws NoActiveTransactionException;
    public boolean isMarkedRollbackOnly();

Get method

An application obtains a Session instance from an ObjectGrid object using the ObjectGrid.getSession method. The following example demonstrates how to obtain a Session instance:

ObjectGrid objectGrid = ...; Session sess = objectGrid.getSession();

After a Session is obtained, the thread keeps a reference to the session for its own use. Calling the getSession method multiple times returns a new Session object each time.

Transactions and Session methods

A Session can be used to begin, commit, or rollback transactions. Operations against BackingMaps using ObjectMaps and JavaMaps are most efficiently performed within a Session transaction. After a transaction has started, any changes to one or more BackingMaps in that transaction scope are stored in a special transaction cache until the transaction is committed. When a transaction is committed, the pending changes are applied to the BackingMaps and Loaders and become visible to any other clients of that ObjectGrid.

WebSphere eXtreme Scale also supports the ability to automatically commit transactions, also known as auto-commit. If any ObjectMap operations are performed outside of the context of an active transaction, an implicit transaction is started before the operation and the transaction is automatically committed before returning control to the application.

Session session = objectGrid.getSession();
ObjectMap objectMap = session.getMap("someMap");
objectMap.insert("key1", "value1");
objectMap.insert("key2", "value2");
objectMap.insert("key3", "value3"); // auto−commit

Session.flush method

The Session.flush method only makes sense when a Loader is associated with a BackingMap. The flush method invokes the Loader with the current set of changes in the transaction cache. The Loader applies the changes to the backend. These changes are not committed when the flush is invoked. If a Session transaction is committed after a flush invocation, only updates that happen after the flush invocation are applied to the Loader. If a Session transaction is rolled back after a flush invocation, the flushed changes are discarded with all other pending changes in the transaction. Use the Flush method sparingly because it limits the opportunity for batch operations against a Loader. Following is an example of the usage of the Session.flush method:

Session session = objectGrid.getSession();
// make some changes
session.flush(); // push these changes to the Loader, but don't commit yet
// make some more changes

NoWriteThrough method

Some eXtreme Scale maps are backed by a Loader, which provides persistent storage for the data in the map. Sometimes it is useful to commit data just to the eXtreme Scale map and not push data out to the Loader. The Session interface provides the beginNoWriteThough method for this purpose. The beginNoWriteThrough method starts a transaction like the begin method. With the beginNoWriteThrough method, when the transaction is committed, the data is only committed to the eXtreme Scale in-memory map and is not committed to the persistent storage that is provided by the Loader. This method is very useful when performing data preload on the map.

When using a distributed ObjectGrid instance, the beginNoWriteThrough method is useful for making changes to the near cache only, without modifying the far cache on the server. If the data is known to be stale in the near cache, using the beginNoWriteThrough method can allow entries to be invalidated on the near cache without invalidating them on the server as well.

The Session interface also provides the isWriteThroughEnabled method to determine what type of transaction is currently active.

Session session = objectGrid.getSession();
// make some changes ...
session.commit(); // these changes will not get pushed to the Loader

Obtain the TxID object method

The TxID object is an opaque object that identifies the active transaction. Use the TxID object for the following purposes:

See TransactionCallback plug-in and Loaders for additional information about the Object slot feature.

Performance monitoring method

If you are using eXtreme Scale within WAS, it might be necessary to reset the transaction type for performance monitoring. You can set the transaction type with the setTransactionType method. See Monitoring ObjectGrid performance with WAS performance monitoring infrastructure (PMI) for more information about the setTransactionType method.

Process a complete LogSequence method

WebSphere eXtreme Scale can propagate sets of map changes to ObjectGrid listeners as a means of distributing maps from one Java™ virtual machine to another. To make it easier for the listener to process the received LogSequences, the Session interface provides the processLogSequence method. This method examines each LogElement within the LogSequence and performs the appropriate operation, for example, insert, update, invalidate, and so on, against the BackingMap that is identified by the LogSequence MapName. An ObjectGrid Session must be available before the processLogSequence method is invoked. The application is also responsible for issuing the appropriate commit or rollback calls to complete the Session. Autocommit processing is not available for this method invocation. Normal processing by the receiving ObjectGridEventListener at the remote JVM would be to start a Session using the beginNoWriteThrough method, which prevents endless propagation of changes, followed by a call to this processLogSequence method, and then committing or rolling back the transaction.

// Use the Session object that was passed in during
// process the received LogSequence
try {
} catch (Exception e) {
    session.rollback(); throw e;
// commit the changes

markRollbackOnly method

This method is used to mark the current transaction as "rollback only". Marking a transaction "rollback only" ensures that even if the commit method is called by application, the transaction is rolled back. This method is typically used by ObjectGrid itself or by the application when it knows that data corruption could occur if the transaction was allowed to be committed. After this method is called, the Throwable object that is passed to this method is chained to the exception that results by the commit method if it is called on a Session that was previously marked a "rollback only". Any subsequent calls to this method for a transaction that is already marked as "rollback only" is ignored. That is, only the first call that passes a non-null Throwable reference is used. Once the marked transaction is completed, the "rollback only" mark is removed so that the next transaction that is started by the Session can be committed.

isMarkedRollbackOnly method

Returns if Session is currently marked as "rollback only". Boolean true is returned by this method if and only if markRollbackOnly method was previously called on this Session and the transaction started by the Session is still active.

setTransactionTimeout method

Set transaction timeout for next transaction started by this Session to a specified number of seconds. This method does not affect the transaction timeout of any transactions previously started by this Session. It only affects transactions that are started after this method is called. If this method is never called, then the timeout value that was passed to the setTxTimeout method of the method is used.

getTransactionTimeout method

This method returns the transaction timeout value in seconds. The last value that was passed as the timeout value to the setTransactionTimeout method is returned by this method. If the setTransactionTimeout method is never called, then the timeout value that was passed to the setTxTimeout method of the method is used.


This method returns boolean true if the current transaction that was started by this Session has timed out.

isFlushing method

This method returns boolean true if and only if all transaction changes are being flushed out to the Loader plug-in as a result of the flush method of Session interface being invoked. A Loader plug-in may find this method useful when it needs to know why its batchUpdate method was invoked.

isCommitting method

This method returns boolean true if and only if all transaction changes are being committed as a result of the commit method of Session interface being invoked. A Loader plug-in might find this method useful when it needs to know why its batchUpdate method was invoked.

setRequestRetryTimeout method

This method sets the request retry timeout value for the session in milliseconds. If the client set a request retry timeout, the session setting overrides the client value.

getRequestRetryTimeout method

This method gets the current request retry timeout setting on the session. A value of -1 indicates that the timeout is not set. A value of 0 indicates it is in fail-fast mode. A value greater than 0 indicates the timeout setting in milliseconds.

Parent topic:

Access data with client applications

Related concepts

ObjectGrid interface

BackMap interface

Interacting with an ObjectGrid using ObjectGridManager

Data access with indexes (Index API)

Access data in WebSphere eXtreme Scale

Cache objects with no relationships involved (ObjectMap API)

Cache objects and their relationships (EntityManager API)

Retrive entities and objects (Query API)

Configure clients with WebSphere eXtreme Scale

HTTP session management

Related tasks

Program for transactions

Configure HTTP session managers

Related reference

Connect to a distributed ObjectGrid


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