To calculate the 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 transactions that have already rolled back
The maximum number of update records in the transaction log that are likely to belong to open transactions at any one time
Update records change the timestamp value, and include changes to data pages, index pages, allocation pages, and so on.
Each rollback record requires approximately 60 bytes of space, or 3/100ths 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.
