It means there was a particularly long/slow database transaction. Frequent occurrences may indicate an opportunity for optimization. Though, offhand, I’m not sure why this particularly one is being logged at the WARN level rather than DEBUG (or at least INFO). It was just added in v29 so that’s why you wouldn’t have seen it previously: Performance considerations — Nextcloud latest Developer Manual latest documentation
But the message is not “Transaction took longer than 1s:” as stated in the documentation. It is “Transaction took <x.xxxxx>s”.
It also appears in log level 2 and not only in log level 0 as documented.
The message is created in “lib/private/DB/Connection.php” under line 685 if getTransactionNestingLevel is 0.
How can I set the TransactionNestingLevel so that this message no longer appears? Even if my database is slow. It is fast enough for me and I would like to disable this message.