Under what circumstances will set emplace fail?

I emplace a new custom class in the set container, in which there is a custom comparison function to sort, and then add two elements An and B in the container. I delete B, change the value of B, and re-emplace B, but validating the returned value will find that the insertion failed.

CPP
May.08,2022
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3e25f-2c41a.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3e25f-2c41a.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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