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.