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Transaction manager services
When to use two-phase commit transactions
One of the basic principals of building high performance distributed applications is to
limit the number of remote procedure calls (RPCs). The following explains typical
situations; when and when not to use two-phase commit transactions. Avoiding a twophase
commit transaction when it is not needed, therefore avoiding unnecessary RPCs
involving JTA XAResource objects and the OTS engine, greatly improves your
application's performance.
Using multiple JDBC connections for access to multiple database
resources from a single vendor in the same transaction
In scenarios involving multiple databases from a single vendor, it is often possible to
avoid using two-phase commit. You can access one database and use it to access the
second database by tunneling access through the connection to the first database.
Oracle and other DBMSs provide this capability. In this case the BES Partition can be
configured with only one JDBC connection to the “fronting” database. Access to the
“backing” database is tunneled through the first JDBC connection.
Using multiple JDBC connections to the same database resource in the
same transaction
When multiple JDBC connections to the same database are obtained and used by
distributed participants within a single transaction, a two-phase commit can be
avoided. The JDBC connections, as expected, need to be obtained from a XA
datasource. But, rather than performing a two-phase commit, a one-phase commit can
be used to complete the transaction since only a single resource is involved. This is
achieved by using the Transaction Manager rather than the OTS engine. An alternative
is to collocate all EJBs involved in the transaction, rather than having them deployed in
distributed Partitions. In this case, a non-XA datasource is used and no two-phase
commit is required.
Note
Using multiple disparate resources in a single transaction
In this case there is a need for a two-phase commit transaction. This situation arises
when, for example, you are running a single transaction against both Oracle and
Sybase, or if you have a transaction that includes access to an Oracle database and a
JMS provider, such as MQSeries. In the latter case, the transaction is coordinated
using JTA XAResource object, obtained from Oracle via JDBC and MQSeries via JMS,
and enables both resources to participate in the two-phase commit transaction
completion. It is worth noting that two-phase commit capabilities (provided by the OTS
engine), are only needed when a single transaction involves access to multiple
incompatible resources.
In order to utilize the OTS engine as the default transaction service, the Transaction
Manager must be stopped first.
170 BES Developer’s Guide