Any trx log file can contain only committed transactions. If you have more than 1 log file, and the first log file is full and can't grow, - the next transaction will start being written to the next trx log file. But that new transaction will have to be completely written to that log file. If it's too large to fit that log file, - it will fail and roll back, even if you have 100 more brand new shiny log files waiting to be used
"The data in a record depends on the Key to the record, the Whole Key, and
nothing but the Key, so help me Codd."