how to estimate the SGA values ?

[vr76413]

Hello all...

Sun 5.8 / Oracle 9.2 and Oracle8.1.7

This is one question that always have at the back of my mind ...

How do we estimate the size of the SGA ?.....Like say when i created a database using DBCA, it already assigns some default SGA values.

Is there a "Rule of Thumb" for assigning SGA values for each instance..?...Most of my databases have atmost 25-50 connections at a given time with about 1GB data. ...

How do we calculate the SGA values for these kinds of Databases ?...

currently i have values ranging from :
320,308,312 to 48,075,571

So can anyone pleas expalin how to estimate the SGA values ?


Thanks
Ron

[supower]

It's mainly depending on how much real memory in your box. General speaking, do not allocate >60% of your box memory for SGA.

[vr76413]

Sun 5.8/Oracle 9.2

So for eg. If my Physical RAM is 1GB and i have 4 Instances each with 400MB and if my SWAP AREA is 1GB....what happens ?...

Will it stop loading from 3rd instance since 800 MB already used for Loading the First 2 Instances ?...
Iam new to DBA and iam trying to figure out the MAth here ...
Thanks

[supower]

The 3rd instance will start and the box will have a lot of PAGING.... make system slow....

[vr76413]

Iam Sorry ...Iam new to DBA ...

So what are my Options to make it work better ?....Increase RAM ?...or SWAP Area ?....

Thanks
Ron

[Shestakov]

Originally posted by vr76413
Iam Sorry ...Iam new to DBA ...

So what are my Options to make it work better ?....Increase RAM ?...or SWAP Area ?....

Thanks
Ron

One of the main rule for dba:
SGA should be in REAL memory and NEVER in swap.

[supower]

Increase RAM.