The product detail page team has strict latency requirements for any content rendered “above the fold“, which refers to any part of a product detail page that you see when the page first loads without scrolling down.
Figure 1: Screenshot of an Amazon product detail page, with a red horizontal line across the image to indicate "the fold" in "above the fold". We consider any content on the detail page above the red line "above the fold".
We've been looking at our latency graphs, and we've discovered that our latency increases almost linearly with the
number of TargetingPredicates in a TargetingGroup. It's probably because each TargetingPredicate calls
the DAOs it needs on its own.
You recall from the KindlePublishingService project that when RecommendationsService was slowing us down, you cached
the calls using an in-memory cache. However, since our service runs on Lambda, our activities can run on
different hosts every time, so any data we save in an in-memory cache will not be there in subsequent calls.
We have learned to perform multiple I/O calls at the same time with an ExecutorService.
By running all the predicates in a targeting group concurrently,
we can choose an ad quickly enough to meet the latency requirements!
Use an ExecutorService to concurrently call the predicates in each group.
You may use a Future to store the results, but that's not required.
You also don't have to use lambda expressions, but they will probably make your code more readable.
Exit Checklist:
- You've implemented your new functionality with unit tests
- Running the gradle command
./gradlew -q clean :test --tests "com.tct.mastery.task2.*"passes. - Running the gradle command
./gradlew -q clean :test --tests com.tct.introspection.MT2IntrospectionTestspasses.