The long-transaction high-watermark is the percentage of total log space that a transaction is allowed to span before it is rolled back. If the database server finds an open transaction in the oldest used log file, it dynamically adds log files. Because the log space is increasing, the high-watermark expands outward. When the log space reaches the high-watermark, the database server rolls back the transaction. The transaction rollback and other processes also generate logical-log records. The database server continues adding log files until the rollback is complete to prevent the logical log from running out of space. More than one transaction can be rolled back if more than one long transaction exists.
For example, the database server has ten logical logs and LTXHWM is set to 98. A transaction begins in log file 1 and update activity fills logs 1 through 9. The database server dynamically adds log file 11 after log file 10. As long as the transaction does not complete, this process continues until the database server has added 40 log files. When the database server adds the fiftieth log, the transaction has caught up to the high-watermark and the database server rolls it back.
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