Re: [Tarantool-patches] [PATCH v3] wal: introduce limits on simultaneous writes

[Konstantin Osipov via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

* Vladislav Shpilevoy <v.shpilevoy@tarantool.org> [21/02/26 23:24]:
> Talking of the other limits - firstly we need to find if some of them
> really overflows. Then yes, such a semaphone-thing could be applied
> there too. But AFAIK, there are no other known similar bugs yet.

Exploring this rather theoretically, since there are no user async
transactions yet, I can imagine such transaction takes up memory
and then blocks on WAL semaphore. If there is no limit on the
number of async transactions, it can be a lot of memory. On the
other hand this can be limited by a yet another semaphore.

> >>> Otherwise your overflow will just spill out someplace else.
> >>
> >> On the contrary. Your proposal to do it in the applier would lead to
> >> queue overflow in some other place - in userspace. When the queue is
> >> for the entire WAL, it won't overflow.
> > 
> > I did  not say it should be in the applier. 
> 
> It was a misunderstanding.

-- 
Konstantin Osipov, Moscow, Russia