Re: (ITS#8958) 2nd cn=config update blocks slapd while adding subordinate index

[h.b.furuseth@usit.uio.no]

On 1/21/19 7:49 PM, OndÅ?ej Kuzník wrote:
> Except there are no locks as you know being the author of parts of
> code that deals with what I'm about to outline anyway:
>
> Whenever a cn=config op is about to be processed, a pause is requested.
> That tells worker threads to stop picking up new work and waits until
> they're all quiet. The indexing task is run by one of these worker
> threads.

Duuh, right.  I got stuck looking for what's special about the
indexing task and couldn't find it:-(  I need to make it special.

So, let tasks declare their expected speed until finish or
between pausechecks.  At FAST=1 (default) and SLOW=0.
A pause only stops tasks with speed < ltp_pause.
In thread_pool_pause(), replace the WANT_PAUSE stage with

   while (++ltp_pause <= max speed) {
     wait until no more tasks with speed < ltp_pause;
   }

Then fast tasks should breeze past slow ones when preparing
to pause.  Until all threads have slow tasks, anyway.

To mitigate that, we'd need to predeclare the speed when
submitting a task, and limit the number of parallel slow
tasks.  pool_submit() could stash the rest in a "slow queue"
instead of submitting.  But I don't want to go there yet.