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Date: Fri, 20 Mar 2020 13:29:56 +0300
From: Cyrill Gorcunov <gorcunov@gmail.com>
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 <20200320081956.30650-12-gorcunov@gmail.com>
 <20200320102254.GB20273@atlas>
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Subject: Re: [Tarantool-patches] [PATCH v15 11/11] box/journal: redesign
	journal operations
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To: Konstantin Osipov <kostja.osipov@gmail.com>, tml <tarantool-patches@dev.tarantool.org>

On Fri, Mar 20, 2020 at 01:22:54PM +0300, Konstantin Osipov wrote:
> * Cyrill Gorcunov <gorcunov@gmail.com> [20/03/20 11:25]:
> > Redesing notes:
> 
> Redesign

+1

> 
> > +int
> > +journal_no_write_async(struct journal *journal,
> > +		       struct journal_entry *entry)
> > +{
> > +	(void)journal;
> > +
> > +	assert(true);
> > +	entry->res = -1;
> 
> You have to set the diagnostics area if you return -1, otherwise
> you'll get a crash in production.

Will, do, thanks!

> 
> > +	return -1;
> > +}
> > +
> > +void
> > +journal_no_write_async_cb(struct journal_entry *entry)
> > +{
> > +	assert(true);
> > +	entry->res = -1;
> 
> Same here.

OK

> 
> > @@ -636,21 +628,28 @@ txn_commit(struct txn *txn)
> >  		return -1;
> >  	}
> >  
> > -	if (txn_write_to_wal(req) != 0)
> > +	fiber_set_txn(fiber(), NULL);
> > +	if (journal_write(req) != 0) {
> > +		fiber_set_txn(fiber(), txn);
> 
> I wonder why do you need to clear/set txn in txn_commit()?

Because async write engine implies that fiber's txn is dropped.
In particular

void
txn_complete_async(struct journal_entry *entry)
{
	struct txn *txn = entry->complete_data;
	txn->signature = entry->res;
	/*
	 * Some commit/rollback triggers require for in_txn fiber
	 * variable to be set so restore it for the time triggers
	 * are in progress.
	 */
-->	assert(in_txn() == NULL);
	fiber_set_txn(fiber(), txn);
	txn_complete(txn);
	fiber_set_txn(fiber(), NULL);
}

Thus to not use txn.h inside journal/wall I clear it before
the write and restore it back in case of error because rollback
needs txn bound to a fiber.

> > +		txn_rollback(txn);
> > +		txn_free(txn);
> > +
> > +		diag_set(ClientError, ER_WAL_IO);
> > +		diag_log();
> >  		return -1;
> > +	}
> >  
> > -	/*
> > -	 * In case of non-yielding journal the transaction could already
> > -	 * be done and there is nothing to wait in such cases.
> > -	 */
> >  	if (!txn_has_flag(txn, TXN_IS_DONE)) {
> > -		bool cancellable = fiber_set_cancellable(false);
> > -		fiber_yield();
> > -		fiber_set_cancellable(cancellable);
> > +		txn->signature = req->res;
> > +		txn_complete(txn);
> > +		fiber_set_txn(fiber(), NULL);
> 
> Seems you do it twice ?

If you mean the txn_complete call then no, in async write
we call the completion wich sets up TXN_IS_DONE flag, in
turn sync write (without wal) doesn't call the completion
and this flag is clear.

Or you meant something different?