Trigger a merge when |CD | reaches a threshold size st relative to |CM | ▪ Fraction of optimum (fro) strategy: □ Trigger a merge at n-th write, if current select cost reach a defined distance fopt from the theoretically opt. cost (|CD |=0) (selectCostopt(n)) □ Since selectCost(n) and selectCostopt(n) are only defined by current size of |CD | and |CM |, both can be easily computed during runtime HYRISE | Martin Grund / Jens Krueger | Nov. 2011 42 efined fraction fopt of selectCostopt(n). Thus, a merge is triggered is true. As selectCost(n) and selectCostopt(n) are defined by the ta structures, both values can easily be calculated at runtime. selectCost(n) > fopt · selectCostopt(n) (4) main (frm) When applying the fraction of main (frm) strategy, gered, whenever |CD | reaches a threshold size st relative to |CM |. st · | CM |<| CD | (5) erge vs. Partial Merge he performance functions defined in Section 2.2 to choose between artial merge whenever a merge event is triggered. If the expected fter a partial merge selectCost P is comparable to that after a full ost F , a partial merge will be executed. We define the factor fto to tolerated overhead with regard to the merge costs saved, thus a s performed whenever (6) evaluates true, a full merge otherwise. If s a dictionary overflow , we always choose a full merge operation. selectCost P ⇥ fto · selectCost F (6) 0 0 0 ion of read optimum (fro) The basic idea of this strategy is to maintain -cost level that has a defined distance to the theoretical optimal read-costs. fine the optimal read-costs after n inserts, denoted by selectCostopt(n), worst case costs of a range query with |CD | = 0, i.e., selectCostopt(n) bes the maximum costs of a range query when the di erential store is fully d into the main store. The fro strategy allows selectCost(n) to grow until eeds a defined fraction fopt of selectCostopt(n). Thus, a merge is triggered time (4) is true. As selectCost(n) and selectCostopt(n) are defined by the f the data structures, both values can easily be calculated at runtime. selectCost(n) > fopt · selectCostopt(n) (4) ion of main (frm) When applying the fraction of main (frm) strategy, ge is triggered, whenever |CD | reaches a threshold size st relative to |CM |. st · | CM |<| CD | (5)