Adaptive Server version 11.9 and later include rollback records in the transaction logs. 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. However, because Adaptive Server does not allocate the space reserved for the rollback records to the transaction log, this space is not reported by either sp_spaceused or dbcc checktable.
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. See “Determining the current space for rollback records” for more information.
