Re: inpricise checkpoint stats

"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote
> "Qingqing Zhou" <zhouqq(at)cs(dot)toronto(dot)edu> writes:
> > The problematic line is "0 written" --
>
> What's your point? Those stats are correct for the current process (or
> if not, better take it up with your kernel vendor) and we've never
> stated that they are anything else than process-local stats. In every
> version of Postgres it's been possible that pages dirtied by one process
> are actually written by some other process --- the bgwriter isn't doing
> anything except altering the probabilities a bit.
>

I mean for other commands, the stats are real for it -- no matter it writes
out its own dirty pages or others. Because the process itself is the *only*
exeuctor. From those numbers, I can roughly figure out why it tooks that
time to finish. But for CHECKPOINT, the process actually is not the
executor.

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.

Regards,
Qingqing