> So I was thinking rest of the RAM (1.5GB) is not being utilised. Hence I
> posted the question.
Yes, you are wasting RAM, and this is very common on 32-bit Oracle
Windows databases, especially servers with 8 gig RAM and a HWM PGA
uasgae of less than 500 meg.
There are two solutions used by most shops. You have two choices, 4GT
or AWE. AWE is best and you can use all of the RAM for Oracle.
In my experience the increased data caching can make a huge difference
and for a dedicated Windowsz server you only need to reserve 20% of
the RAM for the OS, and save the rest for SGA and PGA.
4GT:
- In Windows NT Server v4.0 EE, 4 gig RAM Tuning (4GT) was added which
allows SGA up to 3 gig of memory as opposed to the standard 2 gig.
(Yes, 4GT = 3 gig)
- Gives Oracle up to 50% more memory. (but still not enough)
- For larger systems 64-bit Oracle allows up to 512 gig SGA sizes.
- All that's needed is an added boot.ini switch -- /3GB
AWE:
- AWE (Address Windowing Extension) - Allows 32-bit Windows Oracle to
have up to 64 gig of database buffers.
- Available after Oracle8i (8.1.6).
- Moves database buffers out of the 3GB address space "above the
line", leaving low-memory RAM for more connections, larger sort areas,
etc...
- The Win32 AWE (Address Windowing Extension) calls are used which
provide a fast map/unmap interface to "above the line" RAM.
- When running on a machine with >16GB of RAM, Oracle can either use
the 4GT feature or the memory above 16GB, but not both. This is a
Windows limitation.
- From the Oracle 3 gig address space, we allocate space for a
‘window' onto the whole of the db buffers.
- The size of this window is user-configurable.
- The larger the window, the more buffers are quickly available,
however the larger the window, the less space there is for other
memory structures like shared pool, connections, PGAs, etc.
INSTALLING AWE:
- Set use_indirect_data_buffers=true
- Set AWE_WINDOW_SIZE in the registry to the number of bytes of
address space to use for your window onto extended memory. The
default is 1GB.
- Increase db_cache_size to a higher value up to available memory
Received on Tue Aug 24 2004 - 17:56:42 CDT
