DBA Services and Online Oracle Tutorials.">Some programs and their data or selected parts of these suspended, you may need to be swapped out to main memory to the hard disk to make room for the next scheduled program. Later, when the operating system selects them for execution, exchanged items must be restored from disk to memory. Much research has been devoted to the art of scheduling and swap active programs and data from the immediate effect of excessive swap are performance degradation. Disk IO is relatively much slower than memory reads and writes. And remember that the CPU itself is involved in trading activity. An extreme case, known as surra may bring the system to a snail's pace; In this case, the system is so concerned with the exchange of information between the main memory and the hard disk that performs little or no productive transformation. The inner details of this gym happy are hidden for the average user, but have a general feeling leads to some sympathy for the people who design of operating systems. In practical terms, it also States the old adage that you can never have too much RAM, in a different way in the main memory. This situation is further complicated by the need to remember which programs are suspended, when and why. The operating system needs to store the context of each suspended program can resume execution at the right point with the same values in force at the time of suspension. Contexts are actually snapshots of program counter and registers of the CPU, and contexts are being saved and restored regularly by the operating system, as programs are exchanged. Oracle database itself uses this kind of methodology in own way called SGA. SGA stands for global system area or sometimes also known as shared global area. SGA is populated memory region of operating system. SGA has its own buffer cache to stores recent data access page geheugen's (buffers). During heavy memory use of operating system, as a part of SGA or entire SGA would be swapped out to disk and later back to memory consumed than the heavy CPU and disk IO downshifts. Performance of database and server would be humiliating. All memory regions such as main memory, disk cache, The file system buffer cache and Oracle SGA's are for-improving accessibility and earns more than the performance of the database server using the high end features of the system. But due to wrong configuration or wrong prediction resource usage, the advantages of the memories become losses and demand from users or users of the database are not able to achieve good results from high end server with excellent features. Author is having 15+ years experience and providing DBA Services and Online Oracle Tutorials.
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