Oracle architecture trilogy memory structure: PGA & amp; UGA

PGA is the dedicated memory of a process and never allows access by other processes. You can use the C language to call malloc () allocation during runtime to dynamically scale up or down. Furthermore, PGA will never be allocated in the SGA of oracle, and is always allocated locally by the process. PGA is a key role between a user and an oracle instance. The most sensitive contribution of user experience lies in PGA. The user sends a request that is executed in pga. If hit in pga, no soft resolution is required. This is called soft resolution. The cursor in pga points to the data row in database_buffer_cache. A batch is returned, not one. UGA is your session status. Your session can always access this part of memory. The location of UGA depends on how you connect to oracle. For dedicated server connection, UGA is created in PGA; for shared server connection, UGA is created in SGA. Www.2cto.com. Therefore, PGA contains the process memory and UGA. Manual PGA memory management is controlled by the following parameters: SQL> show parameters area_sizeNAME TYPE VALUE contains invalid bitmap_merge_area_size integer 1048576 create_bitmap_area_size integer 8388608 hash_area_size integer 131072 sort_area_size integer 65536 Automatic Memory Management you do not need to manually set the above parameter values. However, if: 1) workarea_size_policy is set to auto www.2cto.com 2) pga_aggregate_target is set to non-0, automatic memory management pga will be introduced. For OLTP, auto is recommended. For OLAP, manual is recommended. Pga memory allocation involves many aspects, including only the workspace (including the sorting area and hash area) under the control of the database instance. Pga_aggregate_target is an upper limit target, rather than the pre-allocated memory size at startup. If you set this value, it means that you want oracle to use much memory to complete sorting and hashing. The actually allocated space may exceed this value. If we have already exceeded pga_aggregate_target, oracle will close one eye. Our request will fail only when the OS reports that there is no memory. What is oracle doing? It will identify the memory used and reduce the memory size allocated by the workspace accordingly. If the request is sorted again, the disk will be I/O. Author: linwaterbin