vCenter is slow and sluggish after upgrading to 5.1

Scenario: vCenter server was upgraded from 5 to 5.1a and after that the vcenter server became too sluggish and slow.
The inventory service was also taking too much of time to load
In the task manager the memory usage was almost 100%,
most of the memory was eaten by multiple java.exe

What to do: for vcenter being very sluggish, high memory usage by multiple java.exe

vCenter Server

Change the wrapper.java.additional.9 setting in the wrapper.conf file located in <installation_directory>\VMware\Infrastructure\tomcat\conf folder.

1. Open the file and search for wrapper.java.additional.9
2. Change the setting to desired value, in my case 512 MB.
3. Save and close the file.

vCenter Single Sing On

Also here, change the wrapper.java.additional.9 setting in the wrapper.conf file located in <installation_directory>\VMware\Infrastructure\SSOServer\conf folder.

1. Open the file and search for wrapper.java.additional.9
2. Change the setting to desired value, in my case once again 512 MB.
3. Save and close the file.

vCenter Inventory Service

Change the wrapper.java.maxmemory setting in wrapper.conf located in the <installation_directory>\VMware\Infrastructure\Inventory Service\conf folder.

1. Open the file and search for wrapper.java.maxmemory
2. Change the setting to desired value, in my case 1024 MB.
3. Save and close the file.

Profile-Drive Storage Service

Also here, change the wrapper.java.maxmemory setting in wrapper.conf located in the <installation_directory>\VMware\Infrastructure\Profile-Driven Storage\conf folder.

1. Open the file and search for wrapper.java.maxmemory
2. Change the setting to desired value, in my case 512 MB.
3. Save and close the file.

Now that you have changed the settings, restart the services or the vCenter Server for the changes to take effect. Try to tweak around with the settings and find out what best suits your environment.
sincere thanks to : http://defaultreasoning.com/2012/09/27/tweaking-java-exe-memory-usage-on-vcenter-server-5-1/

vcenter inventory service being too slow to start : http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2032828