Oracle Database SGA limitations on 32bit windows

If you have windows 32bit look for the use and setting of PAE/AWE the /3GB flag may be set in the boot.ini file. With the /3GB flag set, only 1 GB is used for the OS, and 3 GB is available for all user threads, including the Oracle SGA. While 3 GB isn’t enough for most production databases, at least it is a step in the right direction.Workarounds are available for using memory above the 4 GB limit. Intel 32-bit processors such as the Xeon processor support Paging Address Extensions for large memory support. MS Win 2K and 2003 support PAE through Address Windowing Extensions (AWE). PAE/AWE may be enabled by setting the /PAE flag in the boot.ini file. The “USE_INDIRECT_BUFFERS=TRUE” parameter must also be set in the Oracle initialization file.

In addition, the DB_BLOCK_BUFFERS parameter must be used instead of the DB_CACHE parameter in the Oracle initialization file. With this method, Windows 2000 Server and Windows Server 2003 versions can support up to 8 GB of total memory. Windows Advanced Server and Data Center versions support up to 64 GB of addressable memory with PAE/AWE.

One limitation of AWE is that only the Data Buffer component of the SGA may be placed in extended memory. Threads for other SGA components such as the Shared Pool and the Large Pool, as well as the PGA and all Oracle user sessions must still fit inside a relatively small memory area.

There is an AWE_WINDOW_SIZE registry key parameter that is used to set the size of a kind of “swap” area in the SGA. This “swap” area is used for mapping data blocks in upper memory to a lower memory location. By default, this takes an additional 1 GB of low memory. This leaves only 2 GB of memory for everything other than the Buffer cache, assuming the /3GB flag is set. If the /3GB flag is not set, only 1 GB of memory is available for the non-Buffer Cache components.

There is always a memory allocation limitation in running Oracle DB on 32bit OS... Linux kernel can be modified to use more memory for Oracle SGA but on Windows 2003 it is always a headache So its better to use x64 Architecture to utilize more RAM for Oracle SGA....