to know what version of exam could be effective and put some weight in my resume while applying for jobs
Well, I can only relate my personal experience. I'm working as EE developer for about 5 years already (before it I was C programmer and electronics developer) - and when I just started with Java I also wondered whether I can interest my potential employers with some Java Certificate.
However, after working in several companies, I found that they are only interested in these certificates when their customers request that certain percent of developers of given projects are certified. It may be necessary, for example, if customer wants to certify the project somehow in order to sold it further.
But in such cases your future employer usually tells you "we want you to have certificate. you have 2-3 months to prepare. if you succeed, we pay the expences."
So to conclude - much more weight is put on resume by your "portfolio" on github, some side projects etc.
If you will get Master in CS - this will also put "additional weight" and I believe increase in salary - especially if you will apply to some project about data warehouse analytics, bigdata etc...
I have gone through that website already
Yes, oracle's site is quite a clumsy thing. See now:
1. Open the page by the link above
2. Above green buttons click "Professional Level Certification"
3. Green buttons will change - choose "Oracle Certified Professional - Java SE 8 Programmer"
4. Now you'll get two links
Oracle Certified Associate, Java SE 8 Programmer - leading to this form
- it is Associate level, required prerequisite
Exam for Professional level itself - this link
P.S. I do not think it is worth getting older certificates as Java 8 added serious changes. Also I'd say that though you can surely stop just at Associate level, without pretending to Professional level - but to be honest the range of topics covered by Associate do not sound impressive