User guide

Double-click on [self invalidateGraphic:graphic]; and you'll get Figure 6-20. This contains one

line of expensive code that tests for nested objects.

Figure 6-20

Source View: SKTGraphicView invalidateGraphic

It is interesting to note that even with this fairly quick analysis we have already identified several glaring

problems. The first problem we found was O(N

) behavior introduced by our code implementation hiding

within functions and the use of abstraction. In general it is good to create and use abstraction in your coding.

However, doing so can unintentionally introduce unnecessary performance pitfalls. Each of these functions is

well conceived locally, but when they are used together they combine to have poor scalability. Second, we

used expensive framework calls (in this case, to the undo manager) inside of a loop. Since undoing each step

of a “select all” operation really isn’t necessary, the expensive call can be moved up to a higher level, in order

to just undo all of the selects at once. This is an example of hoisting functionality to a higher level in the

execution tree. Finally, the invalidateGraphic routine was doing some heavyweight testing, and it would

clearly be worthwhile to see if we can move this testing outside of the inner loops, if possible.

Advanced Session Management and Data Mining

Example: Using Data Mining with a Time Profile

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