In this architecture, messages are processed and prioritized asynchronously. Messages have headers that include priority information, address and identification number. The message server links to the relational DBMS and other data sources. Messaging systems are alternative for wireless infrastructures. Three tier with an application server This architecture allows the main body of an application to run on a shared host rather than in the user system interface client environment. The application server shares business logic, computations and a data retrieval engine. In this architecture applications are more scalable and installation costs are less on a single server than maintaining each on a desktop client. 3-tier architecture provides A greater degree of flexibility Increased security, as security can be defined for each service, and at each level Increased performance, as tasks are shared between servers Two Phase Commit A commit operation is, by definition, an all-or-nothing affair. If a series of operations bound as a transaction cannot be completed, the rollback must restore the system (or cooperating systems) to the pre-transaction state. In order to ensure that a transaction can be rolled back, a software system typically logs each operation, including the commit operation itself. A transaction/recovery manager uses the log records to undo (and possibly redo) a partially completed transaction. When a transaction involves multiple distributed resources, for example, a database server on each of two different network hosts, the commit process is somewhat complex because the transaction includes operations that span two distinct software systems, each with its own resource manager, log records, and so on. (In this case, the distributed resources are the database servers.) Two-phase commit is a transaction protocol designed for the complications that arise with distributed resource managers. With a two-phase commit protocol, the distributed transaction manager employs a coordinator to manage the individual resource managers. The commit process proceeds as follows: Phase 1 Each participating resource manager coordinates local operations and forces all log records out: If successful, respond "OK" If unsuccessful, either allow a time-out or respond "OOPS" Phase 2
In this architecture, messages are processed and prioritized asynchronously. Messages have headers that include priority information, address and identification number. The message server links to the relational DBMS and other data sources. Messaging systems are alternative for wireless infrastructures. Three tier with an application server This architecture allows the main body of an application to run on a shared host rather than in the user system interface client environment. The application server shares business logic, computations and a data retrieval engine. In this architecture applications are more scalable and installation costs are less on a single server than maintaining each on a desktop client. 3-tier architecture provides A greater degree of flexibility Increased security, as security can be defined for each service, and at each level Increased performance, as tasks are shared between servers Two Phase Commit A commit operation is, by definition, an all-or-nothing affair. If a series of operations bound as a transaction cannot be completed, the rollback must restore the system (or cooperating systems) to the pre-transaction state. In order to ensure that a transaction can be rolled back, a software system typically logs each operation, including the commit operation itself. A transaction/recovery manager uses the log records to undo (and possibly redo) a partially completed transaction. When a transaction involves multiple distributed resources, for example, a database server on each of two different network hosts, the commit process is somewhat complex because the transaction includes operations that span two distinct software systems, each with its own resource manager, log records, and so on. (In this case, the distributed resources are the database servers.) Two-phase commit is a transaction protocol designed for the complications that arise with distributed resource managers. With a two-phase commit protocol, the distributed transaction manager employs a coordinator to manage the individual resource managers. The commit process proceeds as follows: Phase 1 Each participating resource manager coordinates local operations and forces all log records out: If successful, respond "OK" If unsuccessful, either allow a time-out or respond "OOPS" Phase 2
dm-ss-solutions.docx