Hello. Lets's imagine a sequence in time: (1) Some transactions commit data (simple table inserts/updates). (2) I get data from a table using select. (3) A CHECKPOINT occurs, data from pg_xlog is copied to actual table data files. Questions: Where does PostgreSQL read data during (2) process? For example, I've got some old data and recently committed data there(but not passed CHECKPOINT). Would it scan both pg_xlog(for committed data that dind't pass CHECKPOINT) and table data files? What happens if an index could be used? Evgeny.
