Re: O(n) tasks cause lengthy startups and checkpoints

On Fri, Dec 3, 2021 at 11:50 PM Bossart, Nathan <bossartn(at)amazon(dot)com> wrote:
>
> On 12/3/21, 5:57 AM, "Bharath Rupireddy" <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
> > On Fri, Dec 3, 2021 at 3:01 AM Bossart, Nathan <bossartn(at)amazon(dot)com> wrote:
> >>
> >> On 12/1/21, 6:48 PM, "Bharath Rupireddy" <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
> >> > +1 for the overall idea of making the checkpoint faster. In fact, we
> >> > here at our team have been thinking about this problem for a while. If
> >> > there are a lot of files that checkpoint has to loop over and remove,
> >> > IMO, that task can be delegated to someone else (maybe a background
> >> > worker called background cleaner or bg cleaner, of course, we can have
> >> > a GUC to enable or disable it). The checkpoint can just write some
> >>
> >> Right. IMO it isn't optimal to have critical things like startup and
> >> checkpointing depend on somewhat-unrelated tasks. I understand the
> >> desire to avoid adding additional processes, and maybe it is a bigger
> >> hammer than what is necessary to reduce the impact, but it seemed like
> >> a natural solution for this problem. That being said, I'm all for
> >> exploring other ways to handle this.
> >
> > Having a generic background cleaner process (controllable via a few
> > GUCs), which can delete a bunch of files (snapshot, mapping, old WAL,
> > temp files etc.) or some other task on behalf of the checkpointer,
> > seems to be the easiest solution.
> >
> > I'm too open for other ideas.
>
> I might hack something together for the separate worker approach, if
> for no other reason than to make sure I really understand how these
> functions work. If/when a better idea emerges, we can alter course.

Thanks. As I said upthread we've been discussing the approach of
offloading some of the checkpoint tasks like (deleting snapshot files)
internally for quite some time and I would like to share a patch that
adds a new background cleaner process (currently able to delete the
logical replication snapshot files, if required can be extended to do
other tasks as well). I don't mind if it gets rejected. Please have a
look.

Regards,
Bharath Rupireddy.