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Date: Fri, 31 Jan 2020 22:44:48 +0300
From: Konstantin Osipov <kostja.osipov@gmail.com>
Message-ID: <20200131194448.GA17326@atlas>
References: <20200124151706.18482-1-gorcunov@gmail.com>
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In-Reply-To: <20200124151706.18482-1-gorcunov@gmail.com>
Subject: Re: [Tarantool-patches] [PATCH] box/txn: do not zap fiber txn
 pointer before txn_write_to_wal completes
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To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: tml <tarantool-patches@dev.tarantool.org>

* Cyrill Gorcunov <gorcunov@gmail.com> [20/01/24 18:18]:
> The txn_write_to_wal operates with txn by own: on success it calls
> txn_entry_done_cb which completes transaction, on error it calls
> txn_rollback which expects the transaction we're rolling back is
> the one the fiber carries in storage.
> 
>  | txn_write
>  |   fiber_set_txn(fiber(), NULL); // zap fiber's storage.txn
>  |   txn_write_to_wal(txn);
>  |     journal_entry_new(..., txn_entry_done_cb, ...)
>  |     if (req == NULL)
>  |       txn_rollback(txn);
>  |         assert(txn == in_txn()); // in_txn()=nil, triggers

Wile I agree this call chain is problematic...


> index bedb57449..060d91536 100644
> --- a/src/box/txn.c
> +++ b/src/box/txn.c
> @@ -583,7 +583,6 @@ txn_write(struct txn *txn)
>  		fiber_set_txn(fiber(), NULL);
>  		return 0;
>  	}
> -	fiber_set_txn(fiber(), NULL);
>  	return txn_write_to_wal(txn);

I believe Georgy added this for a reason - since the current fiber
is no longer locked until the transaction is resumed, it should
be removed from the fiber key (this change AFAIU comes from
parallel applier patch).

I suggest you move this statement inside txn_write_to_wal(). I
can't find a good place for it yet though.

-- 
Konstantin Osipov, Moscow, Russia