![]() ![]() The capacity management plan should include a determination on whether the CPUs should be used more efficiently for the nominal load, or should there be some extra capacity for a burst of activity. Assigning the processes to specific CPU cores, however, can make it impossible to use other CPU cores during peak load bursts. If multiple processes have to share the CPU, the data and instruction cache can be contaminated with the data and instructions from both processes, thus reducing the amount of the cache used effectively. Finally, each of these users will probably require some amount of disk resource (less if they are client-server or web based) let?s give them 5 meg of disk to start apiece, that adds up to 5 gigabytes of disk (give or take a meg or two.It may also be beneficial to dedicate sibling CPUs on a multi-core machine to a single JVM to increase the efficiency of its CPU cache. This leaves 100 concurrent users, of those maybe a second 10 percent will be doing activities that require sort areas, this brings the number down to 10 users each using (from our previous example) 10 megabytes of memory each (100 megabytes.) In addition each of the 100 concurrent users needs approximately 200k of process space (depending on activity, OS and other factors) so we are talking an additional load of 20 megabytes just for user process space. An example would be to assume that of an installed user base of 1000 users, only 10 percent of them will be concurrently using the database. Generally you will need to take a SWAG at how much memory and disk resources each user will require. Naturally a one user database will require fewer resources than a thousand user database. Remember that sort areas can either be a part of the shared pool or a part of the large pool, this too we will cover in a later lesson. ![]() ![]() The final major factor for the SGA would be the size of the sort area, for this size of a database a 10-20 megabyte sort area is about right (depending on the number and size of sorts). The log buffer to support a 50 megabyte redo log file would be a minimum of 5 megabytes maybe as large as 10 megabytes. In most cases the SGA shared pool would size out at around 20-150 megabytes maximum depending on the usage model for the shared SQL areas (covered in a later lesson.) For a 20 gigabyte system the redo logs would most likely run between 20 and 80 megabytes, you would want them mirrored and probably no fewer than 5 groups. For example if the database physical size is 20 gigabytes the database block buffers should size out to around 200 megabytes to 1 gigabyte in size depending on how the data is being used. Generally the database block buffer areas of a database SGA will size out at between 1/20 to 1/100 the physical sum of the total number of database file sizes. ![]()
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