||Oracle Tips by Burleson
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
OPEN_LINKS. The number of database links allowed open
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.
Some System-Specific Notes
Each specific operating system contains certain items that a Remote DBA
needs to be aware of and take into account when installing Oracle.
This section attempts to consolidate these system-specific notes in
There are many different versions of UNIX, including Solaris, AIX,
SV4, and the new kid on the block, Linux (while Linux has been
around since the early 90's it is just now coming to the fore in
business uses, hence the new kid label.) This subsection provides
general guidelines and some specific suggestions for those systems I
have experience with.
On the install for the general-use database, the MAXDATAFILES
parameter defaults to a value of 100. On older versions of UNIX
there may be a kernel-based limit of 60 open files per process. This
can be overcome by altering the OPEN_MAX value in the limits.h file.
Under some versions of UNIX this may be different; to make the
determination, look under configurable kernel parameters. Another
UNIX-specific limit is on the total number of file extents.
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