Hi,
I have a large INBOX (300K+ messages) ; on a regular base, I get IMAP queries that take arount 15 seconds to execute, even small ones - like fetches.
This sometimes for FETCH ops, other times for FLAG ones …
Here is an example of my IMAP client (claws-mail)
[2025-11-17 10:06:27] IMAP> 108 UID FETCH 374195 BODY.PEEK[]
[2025-11-17 10:06:44] IMAP< * 339245 FETCH (UID 374195 BODY[] {3576}
[2025-11-17 10:06:44] IMAP< Ret
[2025-11-17 10:06:44] IMAP< [FETCH data - 3576 bytes]
[2025-11-17 10:06:44] IMAP< [data - 56 bytes]
[2025-11-17 10:06:44] IMAP> 62 NOOP
[2025-11-17 10:06:44] IMAP< 62 OK NOOP completed.
[2025-11-17 10:06:45] IMAP> 109 UID STORE 374195 +FLAGS.SILENT (\Seen)
[2025-11-17 10:07:00] IMAP< 109 OK Store completed (15.264 + 0.000 + 15.263 secs).
I tried to reproduce using a script that fetch / flag / unflag and it does reproduce only sometime when running the script twice (simulating 2 IMAP clients)
Any idea of what setup/config I should improve?
My intuition is this is about lock files (especially inbox index file) but no proof - and no information in the logs.
Thanks for your help - all ideas are welcome!