Re: [tarantool-patches] [PATCH v3 07/14] wal: remove fiber from a journal_entry structure

["Георгий Кириченко" <georgy@tarantool.org>]

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On Thursday, June 13, 2019 5:17:02 PM MSK Vladimir Davydov wrote:
> On Sun, Jun 09, 2019 at 11:44:36PM +0300, Georgy Kirichenko wrote:
> > Use a fiber_cond to signal a condition and wake up a waiting fiber.
> > This relaxes friction between fiber and transaction life cycles.
> 
> I don't see how it relaxes anything ;-)
> 
> Please be more specific when writing comments.
Oh, thanks, I will do it
> 
> > +
> 
> Using a fiber_cond to wake up a single fiber is an overkill. You could
> as well do
> 
> 	while (!entry->done)
> 		fiber_yield_timeout(TIMEOUT_INFINITY);
It is not even possible. In common case (an asynchronous transaction for 
instance) WAL  doesn't know which fiber should be awaken and even does such 
fiber exist. Please consider following case: an applier fired a transaction and 
died. Transaction is finished and could be finalized in any fiber which possible 
doesn't exist in this time. So the one way I see do handle this is to let fiber 
subscribe on transaction done. If you could offer me with better solution I 
would be happy.
> 
> Anyway, I have my reservations re how you handle WAL writer wakeups.
> Please see my comments to the final patch.


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