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

[Vladislav Shpilevoy]

> I'd also question the place where you decided to put this gate.
> The source of the issue is async requests, not WAL, which worked
> fine in absence of async requests. So it's async requests that
> should be gated, not WAL.

In the commit message it is clearly stated why it is in the
journal's code, not just in the applier:

	The feature is ready for `box.commit{is_async=true}`. Once it's
	implemented, it should check whether the queue is full and let the user
	decide what to do next. Either wait or roll the tx back.

Async transactions will be exposed to 'userspace' to be able to reduce
latency for network requests ending with a transaction. They won't have
to wait for WAL write to end.

> 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.