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Oracle Interview Questions And Answers
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The advantages over file system files. I/O will be improved because Oracle is bye-passing the kernnel which writing into disk. Disk Corruption will be very less. 38. What is a Control file ? Database's overall physical architecture is maintained in a file called control file. It will be used to maintain internal consistency and guide recovery operations. Multiple copies of control files are advisable. 39. How to implement the multiple control files for an existing database ? Shutdown the databse Copy one of the existing control file to new location Edit Config ora file by adding new control file.name Restart the database. 40. What is meant by Redo Log file mirrorring ? How it can be achieved? Process of having a copy of redo log files is called mirroring. This can be achieved by creating group of log files together, so that LGWR will automatically writes them to all the members of the current on-line redo log group. If any one group fails then database automatically switch over to next group. It degrades performance. 41. What is advantage of having disk shadowing/ Mirroring ? Shadow set of disks save as a backup in the event of disk failure. In most Operating System if any disk failure occurs it automatically switchover to place of failed disk. Improved performance because most OS support volume shadowing can direct file I/O request to use the shadow set of files instead of the main set of files. This reduces I/O load on the main set of disks. 42. What is use of Rollback Segments In Database ? They allow the database to maintain read consistency between multiple transactions. 43. What is a Rollback segment entry ? It is the set of before image data blocks that contain rows that are modified by a transaction. Each Rollback Segment entry must be completed within one rollback segment. A single rollback segment can have multiple rollback segment entries. 44. What is hit ratio ? |