We want to count the number of time the URL response time exceed the threshold.What measure and aggeration should i choose.
Also we want to charts the graph for the count with response time of that threshold voilation
You will first have create a web request response time measure to calculate when your web request has exceeded your desired threshold. Once that is done, you can then create a threshold violations "Count" measure to record the number of times your initial response time measure has exceed its value. You can add that to an incident with its own threshold to alert when the number of violations exceeds a certain value.
You can create dual axis chart that has the response time measure on one axis and the count measure on another so that you can see how they are correlated.
I'm thinking that might end up showing the count of the PurePaths that included that web request regardless of whether they violated the threshold you set. If that doesn't work and you see the measure is clearly too high I would create the same measure and set the upper severe threshold you want, but use that measure as the source measure in a Thresholds Violations > Count measure where you can also set a threshold for the number of occurrences. You would probably want to use the sum aggregation.