(Sorry, Daniel. Forgot to cc pgsql-hackers.)
Hi, Daniel
    Thanks a lot for your response.
    As I can see for now, in my FYP, as the acyclic schema has the property
that it has a join tree. I will check how many join trees it has and
investigate any best option for the RSN schema. If it does have, I will
modify the planner to just use this join tree if it detects a RSN database,
then no need to use System R to search through all possible join trees. The
implementation is narrow to only RSN schema. It might be too constraint for
Postgres as a generic database system.
    For 'loose index join', I googled it and find the two sites useful to
    This is implemented in MySQL already, while Postgres only emulates the
access method. Do you have any mail thread talking about the current design
and progress?
    About the second topic, so currently TABLESAMPLE is not implemented
inside Postgres? I didn't see this query before, but I googled it just now
and the query seems very weird and interesting.
    Still, do you have any mail thread talking about this?

Best Regards
Huang Qi Victor

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