Rollback records are logged whenever a transaction is rolled back. Servers save enough space to log a rollback record for every update belonging to an open transaction.
If a transaction completes successfully, no rollback records are logged, and the space reserved for them is released.
In long-running transactions, rollback records can reserve large amounts of space.
sp_spaceused syslogs name total_pages free_pages used_pages reserved_pages --------------- --------------- --------------- -------------- -------------- syslogs 5632 1179 3783 670
Checking syslogs: Logical pagesize is 2048 bytes The total number of data pages in this table is 3761. *** NOTICE: Space used on the log segment is 3783 pages (7.39 Mbytes), 67.17%. *** NOTICE: Space reserved on the log segment is 670 pages (1.31 Mbytes), 11.90%. *** NOTICE: Space free on the log segment is 1179 pages (2.30 Mbytes), 20.93%.
If the last chance threshold for the transaction log fires when it seems to have sufficient space, it may be the space reserved for rollbacks that is causing the problem.