[pbs-devel] [PATCH v4 proxmox proxmox-backup 0/7] fix #4182: concurrent group pull/push support for sync jobs

[Christian Ebner]

On 4/4/25 20:01, Max Carrara wrote:
> On Fri Apr 4, 2025 at 3:49 PM CEST, Christian Ebner wrote:
>> Syncing contents from/to a remote source via a sync job suffers from
>> low throughput on high latency networks because of limitations by the
>> HTTP/2 connection, as described in [0]. To improve, syncing multiple
>> groups in parallel by establishing multiple reader instances has been
>> suggested.
>>
>> This patch series implements the functionality by adding the sync job
>> configuration property `parallel-groups`, allowing to define the
>> number of concurrent groups pull/push futures to be instantiated and
>> executed for each job.
>> The property is currently not exposed on the UI, as intended to be
>> set in the config directly for now.
>>
>> Examplary configuration:
>> ```
>> sync: s-8764c440-3a6c
>> 	ns
>> 	owner root at pam
>> 	remote local
>> 	remote-ns
>> 	remote-store push-target-store
>> 	remove-vanished false
>> 	store datastore
>> 	sync-direction push
>> 	parallel-groups 4
>> ```
>>
>> Since log messages are now also written concurrently, prefix logs
>> related to groups, snapshots and archives with their respective
>> context prefix and add context to error messages.
>>
>> Further, improve logging especially for sync jobs in push direction,
>> which only displayed limited information so far.
>>
>> [0] https://bugzilla.proxmox.com/show_bug.cgi?id=4182
> 
> So, I've given the code a good look -- unfortunately it's too late to do
> any additional testing, but I wanted to shoot this out regardless in the
> meantime.
> 
> Code Review
> ===========
> 
> As always, the code quality is pristine -- I like that you're factoring
> things out into little helper functions where applicable instead of
> letting the existing methods grow. Very nice. Also applies cleanly
> and is formatted correctly, naturally. Really can't complain, the
> changes are straightforward and easy to follow.
> 
> There's only a couple little things I spotted; see my comments inline.
> 
> Regarding that large comment about mutexes and atomics: That's something
> I just wanted to mention, so just to make it clear, you don't need to
> apply my suggestion :P It's probably something we should have a look at
> tree-wide for other data structures, too.
> 
> Splendid work as always, anyhow!
> 
> For now, until I get to test this, consider:
> 
> Reviewed-by: Max Carrara <m.carrara at proxmox.com>

Thanks for your efforts on this one, appreciated!

There are however 2 things which make me hesitate with bringing this 
patch series further in its current approach:

- Thomas raised valid concerns about the feasibility of adding such 
parallelism parameters just for the sake of a quick fix [0].

- There was a user report about sync jobs being slow over a VPN 
connection, which resulted in networking adjustments which did 
significantly increase the throughput on his side [1]. He documented 
this in the bugtracker issue upon my request [2].

So I would like to rather investigate if congestion control settings can 
help increase performance for the sync jobs rather than adding the 
parallel group sync for now.

What do you think? (CC'ing also Thomas asking for his opinion).

[0] 
https://lore.proxmox.com/pbs-devel/e5a2dcac-630e-4797-bbbf-f38bc260c2ca@proxmox.com/
[1] https://forum.proxmox.com/threads/164450/post-761198
[2] https://bugzilla.proxmox.com/show_bug.cgi?id=4182#c12