This requires no report reading / merging.
We plan to expose this in the HTTP API, so the UI gets a cheap way of
checking whether the app is currently receiving data from probes.
* Hacky working prototype.
* Operate with time.Duration offset instead of fixed timestamp.
* Polished the backend code.
* Made a nicer UI component.
* Small refactorings of the websockets code.
* Fixed the backend tests.
* Better websocketing and smoother transitions
* Small styling refactoring.
* Detecting empty topologies.
* Improved error messaging.
* Addressed some of David's comments.
* Moved nodesDeltaBuffer to a global state to fix the paused status rendering bug.
* Small styling changes
* Changed the websocket global state variables a bit.
* Polishing & refactoring.
* More polishing.
* Final refactoring.
* Addressed a couple of bugs.
* Hidden the timeline control behind Cloud context and a feature flag.
* Addressed most of @davkal's comments.
* Added mixpanel tracking.
We fell victim to variable shadowing here. Each store would be fed the
original list of report keys, instead of only the ones that weren't
found in the previous store. So if a single report was missing from the
in-process cache, we would then fetch all reports from memcache. And if
that in turn was missing a single report we would fetch all reports from
S3.
We chain report stores for a reason - to reduce latency and, in case of
the in-process cache, eliminate decoding costs. So this bug has a huge
impact on query service performance.
To make matters worse, we return *all* the reports - now possibly in
triplicate. Fortunately, the SmartMerger filters these out, so at least
we were not incurring extra merge costs.
