Just been looking again at the way FSM works. In fsm_search_avail() we essentially have just a single way for working out how to search the tree.
Seems like it would be good to abstract this so that we can implement a number of FSM search strategies * (current) randomize - page selection encourages different backends to access different blocks, thus reducing block contention * cluster - page selection made based around selecting block with freespace nearest current block and we prefer keep-in-sequence to avoid-contention * compact - page selection specifically attempts to find the lowest numbered blocks, so that the table will naturally shrink over time. These are not all mutually exclusive, suggested combinations would be randomize, randomize | cluster, randomize | compact So we don't give up the load spreading behaviour, we just apply the logic at lower levels of the tree only. VACUUM could set the FSM into FSMstrategy = compact when it notices that most of the free blocks are at lower end of table. Or explicitly set during VF replacement utility. FSMstrategy = cluster would be the default if clustering is enabled on a table. FSMstrategy can change via ALTER TABLE ... WITH (fsm_strategy = ...) -- Simon Riggs www.2ndQuadrant.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
