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What is PGA (Program Global Area) in Oracle Database?

  1. PGA
    The Program/ Process Global Area (PGA) is a private memory region that contains the data and control information for a server process. Only a server process can access the PGA. Oracle Database reads and writes information in the PGA on behalf of the server process.
    PGA stands for Process Global Area. This is memory reserved for each process that uses Oracle. It contains the context area. Oracle sets this area's size based on the values of the initialization parameters:
    OPEN_LINKS. The number of database links allowed open per user.
    DB_FILES. The number of database files allowed for the database (up to the value of MAX_DATAFILES).
    LOG_FILES. The maximum number of redo log file groups (up to the value of MAX_LOGFILES).
    The PGA also contains session-related information if MTS is not used.
    In environments where MTS is used, the session information is placed in the SHARED_POOL region of the SGA if the LARGE POOL (in Oracle8,8i and 9i) is not configured.
    This session information consists of the user's private SQL area and other session-specific data. The PGA will always hold the user's stack information. The section of the shared or LARGE POOL allocated for the user is called the UGA, which stands for Users Global Area.
    Another contributor to the memory footprint of each process is the size of the SORT_AREA_SIZE and SORT_AREA_RETAINED_SIZE parameters. When a process executes a sort memory, the size of SORT_AREA_SIZE is allocated to the user. If SORT_AREA_RETAINED_SIZE is also set, then this amount of memory is reduced to that value and allowed to grow to SORT_AREA_SIZE. If the sort requires more space than is specified in SORT_AREA_SIZE, the sort is broken into SORT_AREA_SIZED chunks, which are swapped out to disk as needed.h

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