Re: [Tarantool-patches] [PATCH v17 3/5] qsync: track confirmed_lsn upon CONFIRM packet

[Serge Petrenko via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

22.09.2021 16:05, Cyrill Gorcunov пишет:
> While been investigating various cluster split-brain scenarios and
> trying to gather valid incoming synchro request domains and ranges
> we've discovered that limbo::confirmed_lsn updated not dense enough
> to cover our needs.
>
> In particular this variable is always updated by a limbo owner upon
> write of syncro entry (to a journal) while replica just reads such
> record without confirmed_lsn update, so when the replica become a cluster
> leader it sends a promote request back to the former leader where the
> packet carries zero LSN instead of previous confirmed_lsn and validation
> of such packet won't pass.
>
> Note the packet validation is not yet implemented in this patch so it
> is rather a preparatory work for future.
>
> Part-of #6036
>
> Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
> ---
>   src/box/txn_limbo.c | 14 ++++++++++++++
>   1 file changed, 14 insertions(+)
>
> diff --git a/src/box/txn_limbo.c b/src/box/txn_limbo.c
> index eb9aa7780..959811309 100644
> --- a/src/box/txn_limbo.c
> +++ b/src/box/txn_limbo.c
> @@ -774,6 +774,20 @@ txn_limbo_process_run(struct txn_limbo *limbo,
>   	switch (req->type) {
>   	case IPROTO_RAFT_CONFIRM:
>   		txn_limbo_read_confirm(limbo, lsn);
> +		/*
> +		 * We have to adjust confirmed_lsn according
> +		 * to LSN coming from the request. It is because
> +		 * we will need to report it as old's limbo owner
> +		 * LSN inside PROMOTE requests (if administrator
> +		 * or election engine will make us so).
> +		 *
> +		 * We could update confirmed_lsn on every
> +		 * txn_limbo_read_confirm call but this function
> +		 * is usually called in a couple with
> +		 * txn_limbo_write_confirm, thus to eliminate redundant
> +		 * variables update we make so once but explicitly.
> +		 */
> +		limbo->confirmed_lsn = req->lsn;
>   		break;
>   	case IPROTO_RAFT_ROLLBACK:
>   		txn_limbo_read_rollback(limbo, lsn);
LGTM.

-- 
Serge Petrenko