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ASP.NET PDF Viewer using C#, VB/NETAll computers use memory, which actually consists of a hierarchy of different levels of memory The heart of this hierarchy is main memory, which contains all the instruction executions and data manipulations All main memories are random access memory (RAM), which means that you can read any byte in memory in the same amount of time Typically, you can access main memory data in the 10 100 nanosecond range An important part of the information Oracle stores in the RAM allocated to it is the program code that is executing currently or that has been executed recently If a new user process needs to use the same code, it s available in memory in a compiled form, making the processing time a whole lot faster The memory areas also hold information about which users are locking a certain table, thereby helping different sessions communicate effectively. free barcode add in for excel 2007, free barcode generator for excel 2007, how create barcode in excel 2010, barcode in excel free, excel formula to generate 13 digit barcode check digit, barcode font excel 2007 free download, barcode in excel vba, free barcode generator add-in for excel, creating barcode in excel 2010, microsoft excel 2013 barcode add in,Most important, perhaps, the memory areas help in processing data that s stored in permanent disk storage Oracle doesn t make changes directly to the data on disk: data is always read from the disks, held in memory, and changed there before being transferred back to disk It s common to use the term buffers to refer to units of memory Memory buffers are page-sized areas of memory into which Oracle transfers the contents of the disk blocks If the database wants to read (select) or update data, it copies the relevant blocks from disk to the memory buffers After it makes any necessary changes, Oracle transfers the contents of the memory buffers to disk Oracle uses two kinds of memory structures, one shared and the other process-specific The system global area (SGA) is the part of total memory that all server processes (including background processes) share. The process-specific part of the memory is known as the program global area (PGA), or process-private memory The following sections examine these two components of Oracle s memory in more detail.. The System Global Area (SGA) else swap_color=$red fi echo -e "Memory: $white$tot_mem$normal $tot_mem_unit Free: $white$free_mem$normal \ $fre_mem_unit %Used: $mem_color$perc_mem_used$normal" echo -e "Swap: $white$tot_swap$normal $tot_swap_unit Free: $white$free_swap$normal \ $fre_swap_unit %Used: $swap_color$perc_swap_used$normal" echo The SGA is the most important memory component in an Oracle instance. In large OLTP databases, especially, the SGA is a much larger and more important memory area than the PGA. In data warehousing environments, on the other hand, the PGA can be the more important Oracle memory area, because it critically influences the efficiency of large data sorts and hashes, which are commonly part of analytic computations in data warehouses. The SGA s purpose is to speed up query performance and to enable a high amount of concurrent database activity. Because processing in memory is much faster than disk I/O, the size of the SGA is one of the more important configuration issues when you re tuning the database for optimal performance. When you start an instance in Oracle, the instance takes a certain amount of memory from the operating system s RAM the amount is based on the size of the SGA component in the initialization file When the instance is shut down, the memory used by the SGA goes back to the host system The SGA isn t a homogeneous entity; rather, it s a combination of several memory structures The following are the main components of the SGA: Database buffer cache: Holds copies of data blocks read from data files Shared pool: Contains the library cache for storing SQL and PL/SQL parsed code in order to share it among users It also contains the data dictionary cache, which holds key data dictionary information Redo log buffer: Contains the information necessary to reconstruct changes made to the database by DML operations This information is then recorded in the redo logs by the log writer Java pool: Keeps the state of Java program execution.
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