weiping he <laser(at)qmail(dot)zhengmai(dot)net(dot)cn> writes:
> txn1: txn2:
> begin; begin;
> update table_a set col= col + 1; update table_a set col = col + 1;
> end; end;
> if two transaction begin at exact the same time,
> what's the result of 'col' after both transactions committed
> in Read committed level? it's 3 or 2?
> My understanding is the result is 3,
If the second xact to lock the row is READ COMMITTED, you get 3.
If it's SERIALIZABLE you get an error. In no case will you silently
lose an update.
regards, tom lane