queues: didn’t deal with directly in clojure until core.async
queues are everywhere: even software threads have queues for their execution, and correspond to hardware threads that have their own buffers (queues)
queueing theory: a lot of math, ignore most
performance modeling and design of computer systems: queueing theory in action
closed systems: when produce something, must wait for consumer to deal with it before we can produce something else
ex: repl, web browser
open systems: requests come in without regard for how fast the consumer is using them
adding consumers makes the open systems we build more robust
but: because we’re often adding producers and consumers, our systems may respond well for a good while, but then suddenly fall over (can keep up better for longer, but when gets unstable, does so rapidly)
lesson: unbounded queues are fundamentally broken
three responses to too much incoming data:
drop: valid if new data overrides old data, or if don’t care
reject: often the only choice for an application
pause (backpressure): often the only choice for a closed system, or sub-system (can’t be sure that dropping or rejecting would be the right choice for the system as a whole)
this is why core.async has the puts buffer in front of their normal channel buffer
in fact, queues don’t need buffer, so much as they need the puts and takes buffers; which is the default channel you get from core.async
