Re: [HACKERS] Restricting maximum keep segments by repslots

At Wed, 29 Apr 2020 18:58:16 -0400, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote in
> On 2020-Apr-28, Alvaro Herrera wrote:
>
> > On 2020-Apr-28, Kyotaro Horiguchi wrote:
> >
> > > > Anyway I think this patch should fix it also -- instead of adding a new
> > > > flag, we just rely on the existing flags (since do_checkpoint must have
> > > > been set correctly from the flags earlier in that block.)
> > >
> > > Since the added (!do_checkpoint) check is reached with
> > > do_checkpoint=false at server start and at archive_timeout intervals,
> > > the patch makes checkpointer run a busy-loop at that timings, and that
> > > loop lasts until a checkpoint is actually executed.
> > >
> > > What we need to do here is not forgetting the fact that the latch has
> > > been set even if the latch itself gets reset before reaching to
> > > WaitLatch.
> >
> > After a few more false starts :-) I think one easy thing we can do
> > without the additional boolean flag is to call SetLatch there in the
> > main loop if we see that ckpt_flags is nonzero.
>
> I went back to "continue" instead of SetLatch, because it seems less
> wasteful, but I changed the previously "do_checkpoint" condition to
> rechecking ckpt_flags. We would not get in the busy loop in that case,
> because the condition is true when the next loop would take action and
> false otherwise. So I think this should fix the problem without causing
> any other issues. But if you do see problems with this, please let us
> know.

Checking ckpt_flags then continue makes sense to me.

Thanks for committing.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center