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Date: Fri, 20 Mar 2020 16:33:02 +0300
From: Cyrill Gorcunov <gorcunov@gmail.com>
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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 04:09:05PM +0300, Konstantin Osipov wrote:
> * Cyrill Gorcunov <gorcunov@gmail.com> [20/03/20 14:15]:
> > On Fri, Mar 20, 2020 at 01:58:42PM +0300, Konstantin Osipov wrote:
> > > * Cyrill Gorcunov <gorcunov@gmail.com> [20/03/20 13:34]:
> > > > > >
> > > > > > - 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()?
> > >
> > > Forgive me for being really painful about it, but why not use
> > > different complete callbacks for sync and async wal writes?-)
> > > Under the hood they will still call txn_complete(), but one will
> > > assert, and another will not?
> >
> > Hmm. If I remember correctly we've been planning to use callbacks
> > only for async writes. Actually I can introduce callback helper
> > for sync writes as well but this ruines the whole idea, no?
>
> But aren't you using the same callback for sync and async now?
Yes, but this is only because we _have_ to use callbacks in
wal engine for both sync\async writes. The general architecture
is that - sync writes do _not_have_ to use callbacks.
The use of callback in wal is transparent to the caller. At
least I tried to make it so.
> And if you are not using callback for sync, why do you need to
> manipulate with txn in sync?
>
> I'm lost, I accept it.
Because of wal and async engine in it :(
Look the whole idea is the following:
- journal_write_async always use write_async_cb
- journal_write should not use async write (or
it could but transparently)
- journal_write can complete transaction by self,
for this sake it tests for TXN_IS_DONE bit and
doesn't call for txn_complete if bit is set.
You know, I think we're in good shape right now
and can cleanup the series on top maybe?
> > I can easily hide this bit test inside txn_complete itself and
> > for sync write there will be plain txn_complete call, like
> >
> > txn_commit
> > ...
> > journal_write();
> > ...
> > txn_complete();
>
> My point is simple: can we avoid the whole mess of clearing and
> restoring fiber txn for sync write calls?
Letme think about it. But I would prefer to make it on top.