From mboxrd@z Thu Jan 1 00:00:00 1970
Return-Path: <pbs-devel-bounces@lists.proxmox.com>
Received: from firstgate.proxmox.com (firstgate.proxmox.com [IPv6:2a01:7e0:0:424::9])
by lore.proxmox.com (Postfix) with ESMTPS id DF2041FF16B
for <inbox@lore.proxmox.com>; Thu, 17 Apr 2025 11:30:12 +0200 (CEST)
Received: from firstgate.proxmox.com (localhost [127.0.0.1])
by firstgate.proxmox.com (Proxmox) with ESMTP id 271B0F474;
Thu, 17 Apr 2025 11:30:10 +0200 (CEST)
Date: Thu, 17 Apr 2025 11:29:33 +0200
From: Fabian =?iso-8859-1?q?Gr=FCnbichler?= <f.gruenbichler@proxmox.com>
To: Proxmox Backup Server development discussion <pbs-devel@lists.proxmox.com>
References: <20250416141803.479125-1-c.ebner@proxmox.com>
In-Reply-To: <20250416141803.479125-1-c.ebner@proxmox.com>
MIME-Version: 1.0
User-Agent: astroid/0.16.0 (https://github.com/astroidmail/astroid)
Message-Id: <1744881631.fn7zjvs8b1.astroid@yuna.none>
X-SPAM-LEVEL: Spam detection results: 0
AWL 0.046 Adjusted score from AWL reputation of From: address
BAYES_00 -1.9 Bayes spam probability is 0 to 1%
DMARC_MISSING 0.1 Missing DMARC policy
KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment
SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record
SPF_PASS -0.001 SPF: sender matches SPF record
Subject: Re: [pbs-devel] [RFC proxmox-backup 0/4] implement trash can for
snapshots
X-BeenThere: pbs-devel@lists.proxmox.com
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Proxmox Backup Server development discussion
<pbs-devel.lists.proxmox.com>
List-Unsubscribe: <https://lists.proxmox.com/cgi-bin/mailman/options/pbs-devel>,
<mailto:pbs-devel-request@lists.proxmox.com?subject=unsubscribe>
List-Archive: <http://lists.proxmox.com/pipermail/pbs-devel/>
List-Post: <mailto:pbs-devel@lists.proxmox.com>
List-Help: <mailto:pbs-devel-request@lists.proxmox.com?subject=help>
List-Subscribe: <https://lists.proxmox.com/cgi-bin/mailman/listinfo/pbs-devel>,
<mailto:pbs-devel-request@lists.proxmox.com?subject=subscribe>
Reply-To: Proxmox Backup Server development discussion
<pbs-devel@lists.proxmox.com>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Errors-To: pbs-devel-bounces@lists.proxmox.com
Sender: "pbs-devel" <pbs-devel-bounces@lists.proxmox.com>
On April 16, 2025 4:17 pm, Christian Ebner wrote:
> In an effort to simplify the GC phase 1 logic introduced by commit
> cb9814e3 ("garbage collection: fix rare race in chunk marking phase")
> this patch series implement a trash can functionality for snapshots.
that was fast ;)
> The main intention is to allow snapshot's index files, pruned while
> ongoing phase 1 of garbage collection, to be read and their chunks
> marked as in use as well. This will allow to get rid of the currently
> implemented and rather complex retry looping logic, which could in
> theory lead to failing GC or backups when trying to lock the whole
> group exclusively following the 10-th retry.
I think the other, not really smaller intention is to allow undoing an
accidental/premature deletion/pruning. So we need to consider this
usecase as well when designing the trash can semantics, and ideally
introduce that at the same time so we can properly rule out problems..
> To achieve this, pruning of snapshots does not remove them
> immediately, but rather moves them to a `.trash` subfolder in the
> datastores base directory. This directory will then be cleared before
> starting of GC phase 1, meaning that any index file could be restored
> until the next GC run.
see my comment on patch #3
> This however comes with it's own set of issues, therefore sending
> these patches as RFC for now. Open questions and known limitations
> are:
> - Pruning does not cleanup any space, on the contrary it might
> require additional space on COW filesystem. Should there be a flag
> to bypass the trash, also given that sometimes users truly want to
> remove a snapshot immediately? Although that would re-introduce the
> issue with new snapshot ceration and concurrent GC on a last
> snapshot.
I think it might make sense, but I am not sure how we could avoid the GC
issue (but I think we could design the trash can feature in a way that
we keep the retry logic in GC, but that it only ever triggers in case
such a skip-trash pruning took place in a group).
> - Prune + sync + prune might lead to the same snapshot being pruned
> multiple times, currently any second prune on a snapshot would
> fail. Should this overwrite the trashed snapshot?
this depends on how the trash feature is implemented:
- if it's a mark on the snapshot, then attempting to write the snapshot
again could either fail or overwrite the trashed snapshot
- if the snapshot is moved to a trash can, then we could keep multiple
copies there
> - GC might now read the same index twice, once before it was pruned
> followed by a prune while phase 1 is still ongoing and the second
> time as read from the trash. Not really an issue, but rather a
> limitation.
reading twice is a lot better than never reading ;) I don't think this
should be particularly problematic.
> - Further issues I'm currently overlooking
>
> Christian Ebner (4):
> datastore: always skip over base directory when listing index files
> datastore: allow to specify sub-directory for index file listing
> datastore: move snapshots to trash folder on destroy
> garbage collection: read pruned snapshot index files from trash
>
> pbs-datastore/src/backup_info.rs | 14 ++-
> pbs-datastore/src/datastore.rs | 158 +++++++++++++++----------------
> 2 files changed, 89 insertions(+), 83 deletions(-)
>
> --
> 2.39.5
>
>
>
> _______________________________________________
> pbs-devel mailing list
> pbs-devel@lists.proxmox.com
> https://lists.proxmox.com/cgi-bin/mailman/listinfo/pbs-devel
>
>
>
_______________________________________________
pbs-devel mailing list
pbs-devel@lists.proxmox.com
https://lists.proxmox.com/cgi-bin/mailman/listinfo/pbs-devel