Is it okay to look for new opportunities just after joining a company?

If companies don't think twice before laying off their employees, then you don't have to think twice about changing jobs so soon. Simple as that. At the end of the day , you're replaceable no matter how good you are at your current job.

Big companies like Oracle can afford. Don't feel bad about it. Think of your career and how your profile look.

If you are getting better role why not! However u won’t get good hike on switching so soon

What is technology you are working on ? And experince?

You should definitely look for a switch. No mercy.