Transaction Processing Monitors
TP Monitor A program that controls data transfer between clients and servers in
order to provide a consistent environment, particularly for online transaction
processing (OLTP).
Complex applications are often built on top of several resource managers (such as DBMSs,
operating systems, user interfaces, and messaging software). A Transaction Processing
Monitor, or TP Monitor, is a middleware component that provides access to the services
of a number of resource managers and provides a uniform interface for programmers who
are developing transactional software. A TP Monitor forms the middle tier of a three-tier
architecture, as illustrated in Figure 2.16. TP Monitors provide significant advantages,
including:
n Transaction routing The TP Monitor can increase scalability by directing transactions
to specific DBMSs.
n Managing distributed transactions The TP Monitor can manage transactions that
require access to data held in multiple, possibly heterogeneous, DBMSs. For example,
a transaction may require to update data items held in an Oracle DBMS at site 1, an
Informix DBMS at site 2, and an IMS DBMS as site 3. TP Monitors normally control
transactions using the X/Open Distributed Transaction Processing (DTP) standard. A
DBMS that supports this standard can function as a resource manager under the control
of a TP Monitor acting as a transaction manager. We discuss distributed transactions
and the DTP standard in Chapters 22 and 23.
n Load balancing The TP Monitor can balance client requests across multiple DBMSs
on one or more computers by directing client service calls to the least loaded server.
In addition, it can dynamically bring in additional DBMSs as required to provide the
necessary performance.
n Funneling In environments with a large number of users, it may sometimes be
difficult for all users to be logged on simultaneously to the DBMS. In many cases, we
would find that users generally do not need continuous access to the DBMS. Instead
of each user connecting to the DBMS, the TP Monitor can establish connections
with the DBMSs as and when required, and can funnel user requests through these
connections. This allows a larger number of users to access the available DBMSs with
a potentially much smaller number of connections, which in turn would mean less
resource usage.
n Increased reliability The TP Monitor acts as a transaction manager, performing the
necessary actions to maintain the consistency of the database, with the DBMS acting as
a resource manager. If the DBMS fails, the TP Monitor may be able to resubmit the
transaction to another DBMS or can hold the transaction until the DBMS becomes
available again.
TP Monitors are typically used in environments with a very high volume of transactions,
where the TP Monitor can be used to offload processes from the DBMS server. Prominent
examples of TP Monitors include CICS and Encina from IBM (which are primarily used
on IBM AIX or Windows NT and bundled now in the IBM TXSeries) and Tuxedo from
BEA Systems.
TP Monitor A program that controls data transfer between clients and servers in
order to provide a consistent environment, particularly for online transaction
processing (OLTP).
Complex applications are often built on top of several resource managers (such as DBMSs,
operating systems, user interfaces, and messaging software). A Transaction Processing
Monitor, or TP Monitor, is a middleware component that provides access to the services
of a number of resource managers and provides a uniform interface for programmers who
are developing transactional software. A TP Monitor forms the middle tier of a three-tier
architecture, as illustrated in Figure 2.16. TP Monitors provide significant advantages,
including:
n Transaction routing The TP Monitor can increase scalability by directing transactions
to specific DBMSs.
n Managing distributed transactions The TP Monitor can manage transactions that
require access to data held in multiple, possibly heterogeneous, DBMSs. For example,
a transaction may require to update data items held in an Oracle DBMS at site 1, an
Informix DBMS at site 2, and an IMS DBMS as site 3. TP Monitors normally control
transactions using the X/Open Distributed Transaction Processing (DTP) standard. A
DBMS that supports this standard can function as a resource manager under the control
of a TP Monitor acting as a transaction manager. We discuss distributed transactions
and the DTP standard in Chapters 22 and 23.
n Load balancing The TP Monitor can balance client requests across multiple DBMSs
on one or more computers by directing client service calls to the least loaded server.
In addition, it can dynamically bring in additional DBMSs as required to provide the
necessary performance.
n Funneling In environments with a large number of users, it may sometimes be
difficult for all users to be logged on simultaneously to the DBMS. In many cases, we
would find that users generally do not need continuous access to the DBMS. Instead
of each user connecting to the DBMS, the TP Monitor can establish connections
with the DBMSs as and when required, and can funnel user requests through these
connections. This allows a larger number of users to access the available DBMSs with
a potentially much smaller number of connections, which in turn would mean less
resource usage.
n Increased reliability The TP Monitor acts as a transaction manager, performing the
necessary actions to maintain the consistency of the database, with the DBMS acting as
a resource manager. If the DBMS fails, the TP Monitor may be able to resubmit the
transaction to another DBMS or can hold the transaction until the DBMS becomes
available again.
TP Monitors are typically used in environments with a very high volume of transactions,
where the TP Monitor can be used to offload processes from the DBMS server. Prominent
examples of TP Monitors include CICS and Encina from IBM (which are primarily used
on IBM AIX or Windows NT and bundled now in the IBM TXSeries) and Tuxedo from
BEA Systems.
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