already shut down RSS DHT and channel.The other BT clients are less than tixati.

What is the biggest file in your Tixati profile catalog? channels2.dat? How much is it exactly?

If you have used torrent cache channels, you need to remove them from the local list to delete their data. If you see millions of shared files in the status column, your client still stores it. Fully stop the program to be sure. After next gather they re-appear, but remain empty if you don't connect.

Other possible reason is having a lot of torrents with tens of thousands of files.

Probably just a matter of using the RAM available, offload the hard disks. Or is your total free RAM below, say, 5GB?

RSS was turned off，nothing downloads and uploads，the rest space of disk is 50 Gib，still 750 Mib memory，2 times than Bigly BT 4.0.0 with JAVA 25 (64 bit) Eclipse Adoptium with also thousands RSS not auto download，qbittorrent 5.1.4 is much less than other BT clients.

You are sharing the thumbnails not the screenshots.

Linking full images would be great, but those are easy to figure out.

https://pixhost.to/show/5648/693621325_qq20260210101333.png
https://pixhost.to/show/5680/694044759_qq20260211182807.png
https://pixhost.to/show/5680/694044761_qq20260211182702.png

I guess that downloaded RSS data remains stored on disk and in memory until you remove the old RSS feeds themselves. Try doing that, restarting the program, and checking the size. If that doesn't work, stop, and delete rss2.dat and its backup copy manually, that will clean everything you previously did with RSS.

Now why there is so much data is another question. Maybe it's some error. Maybe you subscribed to full stream producing tens of thousands items per day. You filter them locally by some term, but they are still downloaded. In that case, it's better to subscribe to search or tag results RSS to make filtering happen on the server, and produce a small list of items to download.

the memory become small after deleting RSS2.dat, how can I keep the history RSS and maintain low memory usage？other BT clients with thousands of RSS history won't affect the memory usage.

Why do you keep linking to thumbnails, can't see anything with them. Anyway like the guest did, the last 2 are
https://pixhost.to/show/5794/695875724_qq20260216122344.png
https://pixhost.to/show/5794/695875725_qq20260216122338.png
For everyone's convenience.

The RAM you see in Task Manager is just the working amount. Both qB and Tixati can use the same amount of committed RAM, but qB needs 80MB in use and Tixati 730MB in use to work in the moment apparently.
Tixati is a heavier application so it probably takes more, either way a more useful comparison requires the commit/private bytes. Maybe it also has something to do with Tixati using one large profile file while qB relies on per-entry profile files. Core2.dat versus .fastresumes. Not counting RSS and such, I've not used RSS for qB in years and don't remember how it handles that. Maybe that's just one big file.
You can find commit/close enough to commit in Task Manager's "Information" tab under column "virtual memory" or similar. I use Process Explorer for that info, but it should tell you the same thing. Tixati uses the same amount under TM's virtual memory as PE's Private Bytes on my end.

With 900MB Core2 and 330MB RSS, a fresh start is maybe 5.1GB PB for me.

After about 18 hours for Tixati and 96 hours of qBittorrent..
Tixati 33K total entries, 13.4K set to download with most being magnet links that will never reach the next stage
13GB PB, 7.7GB WS
qBittorrent 9.3K total entries, 2.8K set to download with most being in the torrent stage but stalled.
5.6GB PB and 1GB WS.
Not sure qBittorrent is lighter to run. Maybe at base, but Tixati might scale better after 20K entries.
The mostly-stalled qB usually sits around 0-1% CPU usage, Tixati sits at 8% at all times which is one thread.
Neither does everything better than the other. Doubt there is a torrent client that does everything better.
qB probably works better generally for downloading with under 5K torrent entries loaded, less CPU, less RAM, less whatever probably. Only downside might be that it requires individual files for every torrent entry so any time you want to save the whole session it's 5K files being written and any changes requires writing to any entries you've modified.
qB can have a tag and category, I think for Tixati you can only have one. So you can't filter 2 different systems at once to pinpoint entries more accurately.
But it's probably better to rely on sub-foldering either way. That way you still know what's what outside of qB and Tixati.

IIRC qB has a bug at least with the versions I've used(v4.3.7 and older) where it might take almost nothing at all with 800 or less torrents(Maybe 50MB commit) but then suddenly take 1GB+ with 801 or more. Idk exact numbers for all of that these days as I've always been above 3K entries for at least 3 years now so it always takes around 5.5GB.