What came back

A fifth of a second after the tap, Traversal’s answer arrives, and the first thing in it is a number.

Every response leads with a status codeConcept · lights on your mapstatus codeThe three-digit summary a server puts in every response. 2xx it worked, 3xx look elsewhere, 4xx the request was wrong, 5xx the server itself failed. The first digit alone narrows any investigation.. Case’s parcel earns a 200: received, understood, acted on. The rest of the response says what to do next, and what it says is a thing Act 0 never mentioned. We will get there.

The numbers people remember

Harborview runners have a favourite number, and it is not 200. Years ago, before Traversal, the race sold out in an hour, the old website buckled, and somebody screenshotted the sold-out page failing with its three digits showing: 404, not found. A 4xx says the asking was wrong, which felt like an insult on top of the heartbreak. A 5xx says the answering broke, and the veterans still argue that a 5xx is what that morning truly deserved. Either way the screenshot gets reposted every registration morning, and either way the new system gets compared to it whenever anything looks slow.

The old website left one more ghost. Its registration address still exists, and anyone who follows a years-old bookmark gets a redirectConcept · lights on your mapredirectA 3xx response saying the thing you asked for lives somewhere else, with the new address in a header. The browser follows it automatically, which is why moved pages, shortened links, and HTTP-to-HTTPS upgrades all just work.: a response whose whole message is a forwarding address. The browser follows it without asking. Nobody with the old bookmark has ever noticed.

Molly’s second visit

Three states away, Molly reloads the route page for the something-th time, and it appears instantly. Her first visit this morning took a noticeable moment. This one is immediate, and the difference is not the network being kinder.

Two things govern how fast the web feels. One is bandwidthConcept · lights on your mapbandwidthHow much data a connection can carry over a period of time. The width of the pipe, measured in megabits or gigabits per second. It is capacity, and capacity is a ceiling, never a promise., the width of the pipe between her house and everything else, which will matter enormously on race morning and matters barely at all for one page about one bridge. The other is how much has to travel through the pipe in the first place, and on a second visit the answer is much less. Her browser kept copies.

That keeping is browser cachingConcept · lights on your mapbrowser cachingThe browser’s local store of files it may need again: images, fonts, stylesheets. Return visits reuse the saved copies instead of downloading them again, which is why second visits feel faster and why clearing the cache is an occasional cure.. The course map has not changed since Molly first saw it, her browser suspected as much, and so the map never crossed the wire at all. No trip. No wait. She is looking at her own copy.

A copy that was true when it was made. If that phrase rings a bell, it should: it is the 6:04 problem from lottery day wearing different clothes, and this act is three scenes from naming it properly.