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> [21/02/27 16:22]:
> On 26.02.2021 22:20, Konstantin Osipov wrote:
> > * 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.
> 
> Yes, such transactions will only occupy memory. But the plan is return
> an error from box.commit({is_async}) if the WAL queue is full already.
> Because we don't want to block the async commit in anyway. Better bail
> out earlier and give the user a chance to call normal box.commit() if
> necessary. Or introduce some kind of 'try_async' to block if the queue
> is full, but no block if not full, I don't know. We didn't think on the
> API yet.

There is no point in doing parasitic work in this case -
performing a transaction and then rolling it back. 
> 

-- 
Konstantin Osipov, Moscow, Russia