Paul Randal has written code to determine how much log an operation has generated:
Over the weekend there was a discussion on the MVP distribution list about the sys.dm_tran_database_transactions DMV and how one cannot use it to accurately determine how much log an operation has generated because it doesn’t provide a roll-up of the sub-transaction metrics to the outer transaction. This makes the output somewhat non-intuitive.
The discussion prompted me to write some code I’ve been meaning to do since 2012, when SQL Server 2012 introduced a field in LOP_BEGIN_XACT log records that tracks the transaction ID of the parent transaction, allowing the hierarchy of transactions to be investigated.
The actual code is at the bottom of the article, and is available in a zip file here.
It provides two stored procs, sp_SQLskillsAnalyzeLog and sp_SQLskillsAnalyzeLogInner, with the former making use of the latter, and the latter calling itself recursively.
I’d consider this squarely in the advanced troubleshooting realm. Definitely read the whole thing and Paul’s code.