[Monetdb-developers] some questions

hi, i am a new learner of monetdb.And i have some questions below. 1 when I ran some queries on monetdb,I found that the memory was automatically released by monetdb.And it needs extra time to load data into memory again.I don't know why and if there are some triggers in monetdb? Thank you for helps. 2 how do i see the join path when i run a query? 3 what's source code structure? i want to read the source code .And any advices for better understanding source code. thank, guangliang peng