Oracle Concepts of From Burlson
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Oracle commit Processing A commit is a very important Oracle concept. As users make changes in Oracle, those changes are only visible to the user session making the change and are unrecoverable in the case of a crash. A commit changes all that. When the user tells Oracle to commit the change, Oracle makes the change visible to everyone, and ensures that the change is recoverable. Since RAM is wiped out if you lose power to the computer, all the redo data in th e redo buffer would be lost in a power o utage. o prot ect against this problem, a commit asks Oracle to save the redo to disk, which is permanen t. he redo log disk files are called online redo logs. The V$ views hroughout the ne!t two days lectures you will hear about the "# views. he "# views provide a continually updated look at internal statistics. $o u may hear the "# views called dynamic performance views or tables for this reason. here are appro!imately %&' or more "# views in version (.).*. he views themselves are actually constructed on top of the + structs that are at the heart of the Oracle e!ecutable. he + structs in Oracle are named using a # or -# prefi! and general cant be seen by anyone but the S$S user and then only if a view is created against them. /igure %) shows a sa mple of the layout of the "# tables as e!tracted via a partial screen shot from the Reveal 0et Oracle Administrator " isual 1ict ionary. /igure %)2 3!ample of the "# view relations 4ow are they used5 he "# views are used to e!a mine current performance indicators. 6y using a delta method over several e7ually timed selects trending can be performed. his delta method is how many of the monitoring tools get their information about Oracle performance. A s far as 8 know only one tool , 9recise:S;< from 9recise Soft ware Solutions =also sold as 16uner from 3M+> samples e!ternally directly from memory. ;uest Software is working on e!ternally sampling but 8 am not aware if they have it in production as of this writing. he benefits of e!ternal sampling are that increased sample rates =up to ?? per second> can be obtained with little impact on the Oracle database. 8nternal sampling is prone to the same delays and problems any Oracle internal connection falls prey too, thus limiting the sustained sample ratre that can be obtained without seriously impacting performance.
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