tailieunhanh - OCA /OCP Oracle Database 11g A ll-in-One Exam Guide- P60

OCA /OCP Oracle Database 11g A ll-in-One Exam Guide- P60:There is an ever increasing demand for staff with IT industry certification. The benefits to employers are significant—they can be certain that staff have a certain level of competence—and the benefits to the individuals, in terms of demand for their services, are equally great. Many employers are now requiring technical staff to have certifications, and many IT purchasers will not buy from firms that do not have certified staff. | OCA OCP Oracle Database 11g All-in-One Exam Guide 546 TIP You will find that the DBA is expected to know about everything. Not just the database but also the hardware the network the operating system the programming language and the application. Sometimes only the DBA can see the totality of the environment but no one can know it all so work with the appropriate specialists and build up a good relationship with them. Categories of Failures Failures can be divided into a few broad categories. For each type of failure there will be an appropriate course of action to resolve it. Each type of failure may well be documented in a service level agreement certainly the steps to be followed should be documented in a procedures manual. Statement Failure An individual SQL statement can fail for a number of reasons not all of which are within the DBA s domain but even so he she must be prepared to fix them. The first level of fixing will be automatic. Whenever a statement fails the server process executing the statement will detect the problem and roll back the statement. Remember that a statement might attempt to update many rows and fail partway through execution all the rows that were updated before the failure will have their changes reversed through the use of undo. This will happen automatically. If the statement is part of a multistatement transaction all the statements that have already succeeded will remain intact but uncommitted. Ideally the programmers will have included exceptions clauses in their code that will identify and manage any problems but there will always be some errors that get through the error handling routines. A common cause of statement failure is invalid data usually a format or constraint violation. A well-written user program will avoid format problems such as attempting to insert character data into a numeric field but these can often occur when doing batch jobs with data coming from a third-party system. Oracle itself will try to solve .

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