SGA

[shailendra]

HI FRIENDS

I JUST WANTED TO KNOW WHAT IS THE DRAWBACK OF KEEPING VERY HIGH SGA

ALSO I WANTED TO KNOW WHAT ARE THE THINGS I SHOULD CONSIDER WHILE SIZING THE SGA, I MEAN HOW MUCH THE SIZE OF A SGA SHOULD BE? IS THERE ANY RATIO

THANKS IN ADVANCE
SHAILENDRA

[dave777]

SGA shouldn't be more than system can allocate, or you will
force heavy paging. You also should leave enough memory for OS to operate.

[shailendra]

thanks
but is there any calculation for the sizing the sga?

please advice me

Shailendra

[Sureshy]

In simple terms.

50-60% total memmory.

use OS commands to monitor paging/swapping after each increase.

Do not modify unless you have checked your sga hit ratios.

[julian]

Originally posted by Sureshy
In simple terms.

50-60% total memmory.

That's what many people say but if you have the memory use it! This 60% border is meant for not exceding the RAM after (for example) 100s of session use SORT_AREA_SIZE etc.

[Zaggy]

The 50-60% range is the safe area for almost all people. I think this based on the following:
-- Number of concurrent users (around 10K per session)
-- Sort are size (init.ora and whatever is used)
-- OS paging/swapping thresholds (OS and RAM specific)
-- SGA size (init.ora)

I might be missing somethings, but I think that this is the bulk of it. The 50-60% range has existed for a while and 64bit systems are just starting to take off. So, I would guess with a 64bit systems with large amounts of RAM, let say 20GB, using 75% of it is not a bad thing. Also, on Unix machines the paging and swapping parameters can be adjusted to be much lower. But, setting them to low can cause the system to panic, when it needs RAM the most.