Multi-file background transfer doesn't work

Hello.
I have setting "Maximal number of transfers at the same time" = 9 and expected, that when I transfer a directory (in background), 9 files from it will be transferred at the same time. But this is not the case: only 1 file is transferred ((
But if I manually split the files between 9 tasks – they all will work together.
What I do wrong? Why single background task is not distributed among 9 transfers?

Please attach a full session log file showing the problem (using the latest version of WinSCP).

Making some experiments, I've found the source of problem.
I've started several background tasks, one of them realized (!) multi-file transfer, others -- not :((. The difference was in Transfer Settings.
The one, that performs multi-file transfer, had default "New and updated files only" settings, the others have added "Preserve timestamps, Including directories" and have "Exclude directories" file mask set. As I just added the file mask, I think that the problem is in "Including directories" option.
Am I right?
By the way, why only 9 transfers available?

Yes, multiple connections are not used, when preserving timestamps of directories is enabled:
https://winscp.net/eng/docs/ui_pref_background#fn1

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You can increase the limit beyond 9 with raw configuration option Interface\QueueTransferLimitMax:
https://winscp.net/eng/docs/rawconfig#queuetransferlimitmax
But I do not recommend it for stability reasons.

Yes, multiple connections are not used, when preserving timestamps of directories is enabled

Hmm... You have to print this with BIG letters, and add some message or/and checkbox hint for this option. I've spent a lot of time, trying to understand what's going wrong!

You can increase the limit beyond 9 with raw configuration option Interface\QueueTransferLimitMax. But I do not recommend it for stability reasons.

OK, thank you. Is there a way to speed up the directory listing?
I have a slow source with >500k files, and this takes a while (several hours). Of course, I can switch off the "Calculate total size" option, but in this case I will not know the transfer progress.
Multi-connection listing? Progress in amount of files, not MBytes?

A directory listing cannot be read from the middle in general. Definitely not over SFTP. So multi-connection listing is not possible.

Just as an idea: read the top directory and pass to multi-connections links to subdirectories. Then merge.

That's a possibility, indeed. Thanks.

martin wrote:

Yes, multiple connections are not used, when preserving timestamps of directories is enabled:
...

I tried above configuration. But it does not work. The max connections is still 9. And the configuration in GUI Preferences shows 9 too.

I start WinSCP with
Any idea? Thanks in advance.

@yeung: Make sure you have the latest version of WinSCP.

My test is based on WinSCP 6.3.3 (Build 14916 2024-04-16). I believe it is latest version at this moment.
Is above command proper way to launch more multiple connections?

@yeung: That command increases maximal number of background connections, that can be set on the Preferences dialog beyond, what we consider safe. It does not enable an actual use of that many connections. You have to go to the Preferences dialog and set it:
https://winscp.net/eng/docs/ui_pref_background

I see. Thank you @martin