report: add initial context section

report.md

@@ -38,6 +38,59 @@ systems and related subjects, I was given this internship project to work on.
 
 # Context of the subject
 
+The exchange connectivity layer must route orders as fast possible, to stay
+competitive, reduce transaction costs, and lower latencies which could result in
+lost opportunities, therefore less profits.
+
+It must also take on other duties, due to it being closer to the exchange than
+the rest of the infrastructure. For example, a trading strategy can register
+conditional orders with this service: it must monitor the price of product A and
+X, if product A's cost rise over X's, then it must start selling product B at
+price Y.
+
+A new exchange connectivity service, called the Execution Gateway, is being
+built at IMC, the eventual goal being to migrate all trading strategies to using
+this gateway to send orders to exchanges. This will allow it to be scaled more
+appropriately. However, care must be taken to maintain the current performance
+during the entirety of the migration in order to stay competitive, and the only
+way to ensure this is to measure it.
+
+With that context, let's review my expected tasks once more, and expand on each
+of them:
+
+* Become familiar with the service: before writing the code for the benchmark
+  I must first understand what goes into the process of a trade at IMC, what is
+  needed from the gateway and from the clients in order to run them and execute
+  orders. There is a lot of code at IMC: having different teams working at the
+  same time on different trading service results in a lot of churn. The
+  global execution team was created to centralise the work on core services that
+  must be provided to the rest of the IMC workforce. The global execution
+  gateway is one such project, aiming to consolidate all trading strategies
+  under one singular method to send orders to their exchanges.
+* Write a dummy load generator: we want to send orders under different
+  conditions in order to run multiple scenarios which can model varying cases
+  of execution. Having more data for varying corner cases can make us more
+  confident of the robustness and efficiency of the service. This is especially
+  needed becaue of the various roles that the gateway must fulfill: not only
+  must it act as a bridge for the communication between exchanges and traders,
+  but also as an order executor. All those cases must be accounted for when
+  writing the different scenarios.
+* Benchmark the system under the load: once we can run those scenarios smoothly
+  we can start taking multiple measurements. The main one that IMC is interested
+  in is wall-to-wall latency (abbreviated W2W): the time it takes for a trade to
+  go from a trading strategy to an exchange. The lower this time, the more
+  occasions there are to make good trades.
+  FIXME: probably more context in my notes
+* Analyze the measurements: the global execution team has some initial
+  expectations of the gateway's performance. A divergence on that part could
+  mean that the measurements are flawed in some way, or that the gateway is not
+  performing as expected. Further analysis can be done to look at the difference
+  between mean execution time and the 99th percentile, and analyse the tail of
+  the timing distribution: the smaller it is the better. Consistent timing is
+  more important than a lower average, because we must be absolutely confident
+  that a trade order is going to be executed smoothly, and introducing
+  inconsistent latency can result in bad trades.
+
 # Internship roadmap
 
 # Engineering practices