>>Some questions> >>1) ... multiple users.. In the same session ? Nope, multiple users implies different sessions as different users can't share the same session. Sync scan is available across sessions.
2) Is Secondary Index mandatory for Sync Scan ? As far as I know the two are not related. Sync Scan is projected as a TD mechanism to reduce physical IO by sharing the read operations on the Disk
3) What is "current scan point" ? my understanding is that it means that if Query 1 which is in progress has already gone past a few blocks, when Query 2 started, Q2 can start sharing disk reads from that point on (where Q1 is now).
It's like joining some one reading a book somewhere after a few chapters (Not my idea of reading a book though :-) )
Probably someone familiar with FSG intrinsics can throw more light on the topic.