Re: pg_basebackup throttling doesn't throttle as promised

On Fri, Sep 1, 2017 at 1:32 PM, Jeff Janes <jeff.janes@gmail.com> wrote:

> The "-r" option to pg_basebackup is supposed to throttle the rate of the
> backup.  But it only works properly if the server is mostly idle.
>
> Every non-trivial call to XLogFlush or XLogBackgroundFlush will wake up
> the wal sender (the one which is not really sending wal, but base files),
> and the throttling routine doesn't go back to sleep after being awoke
> early.  Rather, it releases another 32kb of data.
>
>
> Should the basebackup.c throttle sleep in a loop until its time has
> expired?
>
> Or should walsender.c WalSndWakeup not wake a wal sender whose status
> is WALSNDSTATE_BACKUP?
>
> Or both?
>


I'm attaching a patch for each option.  Each one independently solves the
problem.  But I think we should do both.  There is no point in issuing
unnecessary kill system calls, and there may also be more spurious wake-ups
than just these ones.

Cheers,

Jeff