web server - Borland Technical Publications

System Contracts
Transaction Management
Transactional access to multiple EISs is an important and often critical requirement for
enterprise applications. The Connectors supports transaction access to multiple,
heterogeneous EISs - where a number of interactions must be committed together, or
not at all, in order to maintain data consistency and integrity.
VisiConnect utilizes the Borland Enterprise Server's transaction manager and supports
Resource Adapters conforming to the following transaction support levels.
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■
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No Transaction support: if a Resource Adapter supports neither Local
Transactions nor XA Transactions, it is non-transactional. If an application
component uses a non-transactional Resource Adapter, the application component
must not involve any connections to the respective EIS in a transaction. If the
application component is required to involve EIS connections in a transaction, the
application component must use a Resource Adapter which support Local or XA
Transactions.
Local Transaction support: the application server manages resources directly,
which are local to the Resource Adapter. Unlike XA Transactions, local transactions
can neither participate in the two-phase commit (2PC) protocol, nor participate as a
distributed transaction (whereas the transaction context is simply propagated);
instead, local transactions solely target one-phase commit (1PC) optimization. A
Resource Adapter defines the type of transaction support in its Sun standard
deployment descriptor. When an application component requests an EIS connection
as part of a transaction, Borland Enterprise Server starts a local transaction based
on the current transaction context. When the application closes the connection,
Borland Enterprise Server commits the local transaction, and cleans up the EIS
connection once the transaction is completed.
XA Transaction support: a transaction is managed by a transaction manager
external to the Resource Adapter and the EIS. A Resource Adapter defines the type
of transaction support in its Sun-standard deployment descriptor. When an
application component demarcates an EIS connection request as part of a
transaction, the Borland Enterprise Server is responsible for enlisting the XA
resource with the transaction manager. When the application component closes that
connection, the application server unlists the XA resource from the transaction
manager, and cleans up the EIS connection once the transaction is completed.
In compliance with the Connectors 1.0 specification, VisiConnect provides full
support for all three specified transaction levels.
One-Phase Commit Optimization
In many cases, a transaction is limited in scope to a single EIS, and the EIS resource
manager performs its own transaction management - this is the Local Transaction. An
XA Transaction can span multiple resource managers, thus requiring transaction
coordination to be performed by an external transaction manager, typically one
packaged with an application server. This external transaction manager can either use
the 2PC protocol, or propagate the transaction context as a distributed transaction, to
manage a transaction that spans multiple EISs. If only one resource manager is
participating in an XA Transaction, it uses the 1PC protocol. In an environment where a
singleton resource manager is handling its own transaction management, 1PC
optimization can be performed, as this involves a less expensive resource than a 1PC
XA Transaction.
Chapter 26: VisiConnect overview 249