I am a PHP developer and the title basically says it all. However I was hoping on some more in-depth information as I am starting to get confused about how the flow for the project I work on should go.

For an (web) application I need to implement a feature like Facebook does it with notifying users about replies/comments and instantly showing these.

I figured I could use long-polling with ajax requests but this does not seem to be a nice solution as the notifications never really are instant and it is resource heavy.

So I should use some form of sockets if I understand correctly, and Node.Js would be a good choice. So based on the last assumption I now get confused about the work flow.

I thought about two possible solutions:

1) It seems to me, that if I would use Node.Js I could skip using PHP at all and base the application on Node.js only.

2) Or I could use PHP as a base and only use Node.js for notifying users and instantly showing messages but saving the data using PHP and Mysql.

These two possibilities confuse me and I can't make up my mind about what would be the "best" and cleanest way.

I do not have much experience in Node.js, played with it for a while. But managing and saving data seems to be hard in Node.js so that is why I came up with option 2. 

I know Facebook is build on PHP so I am assuming that they save the data via PHP and notify / instantly show replies and comments via Node.

Could someone help me out on this? 

Thanks in advance!

**EDIT:** 
I just noticed, Stackoverflow does something similar. I get a notification in the upper left, and below my question a box with "new answer to this question". I am really interested in the technologie(s) used.