To calculate the increased amount of space to add to a transaction log to accommodate rollback records, estimate:
The number of update records in the transaction log that are likely to belong to already rolled-back transactions
The maximum number of update records in the transaction log that are likely to belong to open transactions at any one time
Update records are the records that change the timestamp value. They include changes to datapages, indexpages, allocation pages, and so on.
Each rollback record requires approximately 60 bytes of space, or 3 one hundredths of a page. Thus, the calculation for including rollback records (RRs) in the transaction log is:
Added space, in pages = (logged RRs + # open updates) X 3/100.
You may also want to add log space to compensate for the effects of rollback records on the last-chance threshold and on user-defined thresholds, as described in the following sections.
