Swap space Calculation

Refer MOS Doc: 286388.1

There are two swap memory allocation algorithms, used widely.
1. Eager Allocation Model
This algorithm preallocates swap at the time of process creation.
2. Lazy Allocation Model
In this swap is allocated on-demand. (Called Paging).

In Eager model, 
Minimum swap required = Total virtual memory of all the processes on the Machine

In Lazy Model:
Minimum swap required = Total virtual memory of all processes - Size of RAM

In both models, the Virtual Memory is calculated using, the following sql (in peak time)

select (value/1024/1024)+(select (sum(st.value )/1024/1024)
 from v$sesstat st , v$statname sn
where st.statistic# = sn.statistic#
and sn.name like '%ga memory') "Virtual Memory" 
from v$parameter 
where name='sga_max_size'
;




For 32-bit machines swap can be 
Minimum of 400Mb or 2* size of RAM which ever is greater.
OR
If physical RAM < 2GB , swap = 2* Physical RAM
If Physical RAM >2B & <4GB swap = Size of Physical RAM
If Physical RAM > 4GB swap = 4GB