From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <v.shpilevoy@tarantool.org>
Received: from smtp44.i.mail.ru (smtp44.i.mail.ru [94.100.177.104])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (No client certificate requested)
 by dev.tarantool.org (Postfix) with ESMTPS id 01F11445320
 for <tarantool-patches@dev.tarantool.org>;
 Sun,  5 Jul 2020 18:29:44 +0300 (MSK)
From: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
References: <cover.1593472477.git.v.shpilevoy@tarantool.org>
 <d6cf4d6c5382b0248fb86e470d05dece2e292360.1593472477.git.v.shpilevoy@tarantool.org>
Message-ID: <ee969871-2180-6093-91f7-2756f20f05e7@tarantool.org>
Date: Sun, 5 Jul 2020 17:29:43 +0200
MIME-Version: 1.0
In-Reply-To: <d6cf4d6c5382b0248fb86e470d05dece2e292360.1593472477.git.v.shpilevoy@tarantool.org>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Subject: Re: [Tarantool-patches] [PATCH v2 10/19] txn_limbo: add ROLLBACK
 processing
List-Id: Tarantool development patches <tarantool-patches.dev.tarantool.org>
List-Unsubscribe: <https://lists.tarantool.org/mailman/options/tarantool-patches>, 
 <mailto:tarantool-patches-request@dev.tarantool.org?subject=unsubscribe>
List-Archive: <https://lists.tarantool.org/pipermail/tarantool-patches/>
List-Post: <mailto:tarantool-patches@dev.tarantool.org>
List-Help: <mailto:tarantool-patches-request@dev.tarantool.org?subject=help>
List-Subscribe: <https://lists.tarantool.org/mailman/listinfo/tarantool-patches>, 
 <mailto:tarantool-patches-request@dev.tarantool.org?subject=subscribe>
To: tarantool-patches@dev.tarantool.org, sergepetrenko@tarantool.org

> diff --git a/src/box/txn_limbo.c b/src/box/txn_limbo.c
> index ac57fd1bd..680e81d3d 100644
> --- a/src/box/txn_limbo.c
> +++ b/src/box/txn_limbo.c
> @@ -127,33 +141,64 @@ txn_limbo_wait_complete(struct txn_limbo *limbo, struct txn_limbo_entry *entry)
> -/**
> - * Write a confirmation entry to WAL. After it's written all the
> - * transactions waiting for confirmation may be finished.
> - */
>  static int
> -txn_limbo_write_confirm(struct txn_limbo *limbo, struct txn_limbo_entry *entry)
> +txn_limbo_write_confirm_rollback(struct txn_limbo *limbo,
> +				 struct txn_limbo_entry *entry,
> +				 bool is_confirm)
>  {
>  	struct xrow_header row;
>  	struct request request = {
>  		.header = &row,
>  	};
>  
> -	if (xrow_encode_confirm(&row, limbo->instance_id, entry->lsn) < 0)
> +	int res = 0;
> +	if (is_confirm) {
> +		res = xrow_encode_confirm(&row, limbo->instance_id, entry->lsn);
> +	} else {
> +		/*
> +		 * This entry is the first to be rolled back, so
> +		 * the last "safe" lsn is entry->lsn - 1.
> +		 */
> +		res = xrow_encode_rollback(&row, limbo->instance_id,
> +					   entry->lsn - 1);

Why can't you write the exact lsn + change the check in txn_limbo_read_rollback()
from

    if (e->lsn <= lsn)
        break;

to

    if (e->lsn < lsn)
        break;

Currently the rollback entry contains LSN which counter-intuitively shouldn't be
rolled back.