How do I increase default DBD cache size

[Ramprasad]

I was reading performance tuning information at 

http://cyrusimap.web.cmu.edu/imapd/install-perf.html
I too have a large cyrus setup with minimum  600+ connections at a time
We are upgrading to a 8GB Ram Dual Xeon box , I want to make sure we use
the hardware optimally 

The document talks of increasing cache size in cyrus source which file
do I change ? 

I made this change to the source ( patch file ). Will it work 



Index: lib/imapoptions
===================================================================
--- lib/imapoptions     (.../cyrus-2.3.7-DEFAULT)       (revision 134)
+++ lib/imapoptions     (.../cyrus)     (revision 134)
@@ -155,7 +155,7 @@
    creating the mailbox INBOX.  The user's quota is set to the value
    if it is positive, otherwise the user has unlimited quota. */

-{ "berkeley_cachesize", 512, INT }
+{ "berkeley_cachesize", 4096, INT }
 /* Size (in kilobytes) of the shared memory buffer pool (cache) used
    by the berkeley environment.  The minimum allowed value is 20.  The
    maximum allowed value is 4194303 (4GB). */


Thanks
Ram