Re: inpricise checkpoint stats

"Qingqing Zhou" <zhouqq(at)cs(dot)toronto(dot)edu> writes:
> I raise this problem because (1) I want to add a stat number for xlog
> write/sync; (2) Considering we may have a background xlog writer (discussed
> long time before), the stats may become pointless for local process.

The bgwriter is already capable of pushing xlog data to disk --- it must
do so to guarantee the invariant that xlog hits disk before data-file
change. I think it could do with some tweaking to make it more probable
that the bgwriter issues such writes rather than a regular backend, but
it can happen now. And even without the bgwriter, xlog data your
process created could be forced to disk by some other backend if the
other backend wants to commit before you do.

I'm not entirely sure that the getrusage stats ever meant a lot for
Postgres; they're certainly a pretty incomplete view of what's going
on now.

regards, tom lane