Another question about using shmop!

I read about the php manual, I find that, shmop function can let me use to store information directly on a shared segment memory. However, I have some question about these! Does it provide a faster performance, if I use these rather than store things in mysql DB, I know this might be stupid, but I have to make sure this. And, can I shared the segment ( the data stored inside ) with different user session. Would you show me how. Lastly, is there any further information about using this? the manual only take a little bit!! Thanks Zenith