Oracle memory-instant attack (I)

Oracle memory: memory architecture: oracle database allocates memory and background processes whenever the database instance is started, the following information is stored in the memory area: program code and connection session information, even if the session is not active." Information required during program execution, information about data sharing locks. Buffered data, data blocks, redo log records, and so on. You can check the figure above: A) The basic memory structure includes the following parts: 1) sga (system global area) sga has many shared memory structures, the sga component contains some instance data information and control information, which is shared by all service processes and background processes. For example, data is stored in sga, including cached data blocks and shared SQL areas. 2) pga (program global area) is an area that is owned by an oracle process alone rather than shared. It contains some data and control information. The region is created when the oracle process starts. Pga exists for each service process and background process. All service processes and all pga allocated by the background process lock become the instance pga size. Oracle can only limit the size of all pga and cannot set the size of pga for a single process. 3) uga saves session information of some users. 4) software code zone (software code areas) is a region that stores executed code or code that can be executed. B) oracle database memory management is to maintain the oracle memory structure size based on the database's constant changes, and give the memory-related components a reasonable value. Oracle memory management is performed by setting parameters in the relevant parameter files.

This includes the following management methods: 1) the automatic memory management dba can specify a total target memory value, then, the database instance automatically adjusts the memory size based on different requirements for memory-related components, that is, dynamically adjusts the size of pga and sga based on the requirements for installing different memory. (This content will be further studied later) 2) automatic memory Sharing management (automatic shared memory management) This management mode is an automatic management of a part of the memory. You can set a total size target value for sga and then set a total pga size memory value for management. 3) manual memory management (manual memory management) manual memory management is not to set a maximum value of the target, but to manually manage each memory component through relevant parameters in the parameter file. (This method is cumbersome and discarded.) note: In the 11g scenario, if you use dbca when creating a database and select the basic mode, automatic memory management is used by default.