All databases have a last-chance threshold, including master. The threshold is an estimate of the number of free log pages that are required to back up the transaction log. As you allocate more space to the log segment, Adaptive Server automatically adjusts the last-chance threshold.
When the amount of free space in the log segment falls below the last-chance threshold, Adaptive Server automatically executes a special stored procedure called sp_thresholdaction. (You can specify a different last-chance threshold procedure with sp_modifythreshold.)
Figure 15-1 illustrates a log segment with a last-chance threshold. The shaded area represents log space that has already been used; the unshaded area represents free log space. The last-chance threshold has not yet been crossed.
Figure 15-1: Log segment with a last-chance threshold
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