Today's SQL Server mystery involved runaway tempdb space usage.
I had some existing queries that show what was occupying space in tempdb (internal objects, user objects, version store, etc.) In my particular situation, it was Version Store usage.
I discovered the sys.dm_tran_version_store_space_usage DMV (see link), which pointed me to a user database with no open transactions (I'm still not sure what to think of that).
(Cont'd)
https://learn.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-tran-version-store-space-usage?view=sql-server-ver16
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