Database Reference
In-Depth Information
Figure 29-5.
Data modifications: CHECKPOINT
At this time, pages in the data file store data from uncommitted transaction T1. However, log records in the transaction
log have enough information to undo the changes if needed. When this is the case, SQL Server performs
compensation
operations
, which execute the opposite actions of the original data modifications and generate
compensation log records.
Figure
29-6
shows such an example. SQL Server performed a compensation update generating the compensation
log record with an LSN of 7219 to reverse the changes of the original update operation with an LSN of 7214. It also
generated a compensation insert with an LSN of 7920 to compensate the delete operation with an LSN of 7216.
Figure 29-6.
Data modifications: ROLLBACK
