Hi, I noticed that the numbers in pg_stat_io dont't quite add up to what I expected in write heavy workloads. Particularly for checkpointer, the numbers for "write" in log_checkpoints output are larger than what is visible in pg_stat_io.
That partially is because log_checkpoints' "write" covers way too many things, but there's an issue with pg_stat_io as well: Checkpoints, and some other sources of writes, will often end up doing a lot of smgrwriteback() calls - which pg_stat_io doesn't track. Nor do any pre-existing forms of IO statistics. It seems pretty clear that we should track writeback as well. I wonder if it's worth doing so for 16? It'd give a more complete picture that way. The counter-argument I see is that we didn't track the time for it in existing stats either, and that nobody complained - but I suspect that's mostly because nobody knew to look. Greetings, Andres Freund
