HI all, apologize me for my stupid questions but I'd like to better understand how mvcc works. Now, each tuple has xmin (insert xid) and xmax (delete/update xid). In short each transaction with xmin<=xid<=xmax can see such tuple, otherwise it cannot (of course beeing xmin and xmax different transtaction from xid and beeing committed), isn't it? Now, for subtrans the xid is laizyly obtained, due to efficiency purposes. But in such way subtrans xid should be greater than each other xid of concurrent (main) transactions. If the subtrans inserts a record is the subtrans xid placed in xmin? Because in this case the xmin value makes the tuple invisible to every other concurrent transaction started with the parent one. Is this true or do the subtrans commit with the parent xid (in this case why the subtrans should have a xid?)? Ok, I'm bit confused here.... Finally, the pg_class.relfrozenxid should not be set to the frozen value specified in transam.h when vacuum is executed? And what is its meaning for a newly created table (I see a value that I cannot understand)? Thanks, Luca
