Adaptive Servers that use rollback records must reserve additional room for the last-chance threshold. The last-chance threshold (“LCT”) is also likely to be reached sooner because of the space used by already logged rollback records and the space reserved against open transactions for potential rollback records. Figure 31-4 illustrates how space is used in a transaction log with rollback records:
Figure 31-4: Space used in log with rollback records
In Figure 31-4, in the 11.9 Adaptive Server, log space is occupied by logged rollback records for closed transactions that did not complete successfully. In addition, space is reserved for rollback records that may need to be logged, if any of the currently open transactions do not complete successfully. Together, the space for logged rollback records and for potential rollback records is likely to be considerably greater than the extra space for the last-chance threshold. Consequently, transaction logs that use rollback records reach the last-chance threshold significantly sooner than transaction logs that do not use rollback records, even if the size of the transaction log is not increased.
In general, about 18 percent more log space is reserved for the last-chance threshold in 11.9 and later Adaptive Servers than in earlier versions. For example, for a transaction log of 5000 pages, version 11.5 reserves 264 pages and version 11.9 reserves 312 pages. This is an increase of 18.18 percent between version 11.5 and 11.9.
