Database Reference
In-Depth Information
memory architecture is also called PGA or Program Global Area. The
utilization of PGA depends how you configure the Oracle Server.
Unlike SGA where RAM is shared by all the background process, PGA
is utilized by server process for sorting, session information and as
stack space. Oracle Server can be configured to run as Dedicated
Server mode or Shared Server mode.
Similarly Oracle utilizes RAM too for the same purpose what
other programs does i.e. speedy processing. How that RAM is
categorized or what's its architecture, that's exactly what is
shown in the Figure 4-6. The RAM or simply memory, occupied
by Oracle is divided into two major categories. One is called
Shared Memory and the other one is called Non Shared Memory.
Oracle allocates SGA (System Global Area) whenever Instance
starts and deallocates it when the Instance ends. In OracleRAC
(Oracle Real Application Cluster, used to be called as Oracle
Parallel Server) multiple Instances can access the same database
and we can achieve performance using load balancing etc, each
instance has its own SGA. The study of OracleRAC (multiple
instances and one database) is beyond the scope of this topic but
you cannot jump on to that topic without mastering Oracle
system with one instance and one database. If you have full
mastery over the topics discussed in this topic then learning and
implementing OracleRAC will be piece a cake.
Shared Memory is shared among all connected users with the
Oracle Instance i.e. if one user has submitted the SQL statement
from Canada and another user in Japan has submitted the same
SQL statement, if its parsed version is available in SGA, Oracle
uses that instead
of reparsing.
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