The server process allocates memory structures that it requires in the PGA.Īn analogy for a PGA is a temporary countertop workspace used by a file clerk. The PGA is a memory heap that contains session-dependent variables required by a dedicated or shared server process. Because the PGA is process-specific, it is never allocated in the SGA. The PGA is memory specific to an operating process or thread that is not shared by other processes or threads on the system. When using a dedicated server connection, the UGA is stored in the PGA. Therefore, the UGA is stored in the SGA when using shared server connections, enabling any shared server process access to it. For this reason, the UGA cannot be stored in the PGA when using a shared server connection because the PGA is specific to a single process. The UGA must be available to a database session for the life of the session. An OLAP session opens automatically whenever a user queries a dimensional object such as a cube. The page pool is allocated at the start of an OLAP session and released at the end of the session. This pool manages OLAP data pages, which are equivalent to data blocks.
The OLAP page pool is also stored in the UGA. By default, the package variables are unique to and persist for the life of the session. The package state changes when a package subprogram changes the variables. If a session loads a PL/SQL package into memory, then the UGA contains the package state, which is the set of values stored in all the package variables at a specific time. If you create a database with Database Configuration Assistant (DBCA) and choose the basic installation option, then automatic memory management is the default.ĭescription of "Figure 14-2 User Global Area (UGA)" Instead of setting the total memory size, you set many initialization parameters to manage components of the SGA and instance PGA individually. You set a target size for the SGA and then have the option of setting an aggregate target size for the PGA or managing PGA work areas individually. This management mode is partially automated. The instance automatically tunes to the target memory size, redistributing memory as needed between the SGA and the instance PGA. You specify the target size for the database instance memory. The basic options for memory management are as follows: Oracle Database manages memory based on the settings of memory-related initialization parameters. Memory management involves maintaining optimal sizes for the Oracle instance memory structures as demands on the database change. The following figure illustrates the relationships among these memory structures.
#Large amount of private cache software#
Oracle Database code is stored in a software area that is typically at a different location from user programs-a more exclusive or protected location. Software code areas are portions of memory used to store code that is being run or can be run. The UGA is memory associated with a user session. Database initialization parameters set the size of the instance PGA, not individual PGAs. The collection of individual PGAs is the total instance PGA, or instance PGA. One PGA exists for each server process and background process. Oracle Database creates the PGA when an Oracle process starts. Examples of data stored in the SGA include cached data blocks and shared SQL areas.Ī PGA is a nonshared memory region that contains data and control information exclusively for use by an Oracle process. All server and background processes share the SGA. The SGA is a group of shared memory structures, known as SGA components, that contain data and control information for one Oracle Database instance. The basic memory structures associated with Oracle Database include: Oracle Database includes several memory areas, each of which contains multiple subcomponents.
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