suzanne.soy/shields
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Send cached badge directly if statistically accurate.

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See rationale here:
<https://github.com/badges/shields/issues/161#issuecomment-41812007>.
This commit is contained in:
Thaddee Tyl 2014-05-02 17:16:07 +00:00
parent 0a4bcd6ff9
commit 99d490e1c3
2 changed files with 43 additions and 15 deletions
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1
lru-cache.js
View File

@ -17,6 +17,7 @@ function addToCache(cacheIndex, cached) {
this.order.splice(this.cache[cacheIndex].index, 1);
// Put the new element at the end of `order`.
this.cache[cacheIndex].index = this.order.length;
this.cache[cacheIndex].content = cached;
this.order.push(cacheIndex);
} else {
// If the cache is full, remove the oldest data

57
server.js
View File

@ -94,8 +94,18 @@ camp.ajax.on('analytics/v1', function(json, end) { end(analytics); });
// Cache
var cacheTimeout = 60000; // 1 minute.
var cacheFromIndex = Object.create(null);
// We avoid calling the vendor's server for computation of the information in a
// number of badges.
var minAccuracy = 0.75;
// The quotient of (vendor) data change frequency by badge request frequency
// must be lower than this to trigger sending the cached data *before*
// updating our data from the vendor's server.
// Indeed, the accuracy of our badges are:
// A(Δt) = 1 - min(# data change over Δt, # requests over Δt)
// / (# requests over Δt)
// = 1 - max(1, df) / rf
var freqRatioMax = 1 - minAccuracy;
// Request cache size of size 1_000_000 (~1GB, 1kB/image).
var requestCache = new LruCache(1000000);
@ -108,10 +118,12 @@ function cache(f) {
var cacheIndex = match[0] + '?label=' + data.label + '&style=' + data.style;
// Should we return the data right away?
var cached = cacheFromIndex[cacheIndex];
if (cached != null) {
badge(cached.badgeData, makeSend(cached.format, ask.res, end));
return;
var cached = requestCache.get(cacheIndex);
var cachedVersionSent = false;
if (cached !== undefined
&& cached.dataChange / cached.reqs <= freqRatioMax) {
badge(cached.data.badgeData, makeSend(cached.data.format, ask.res, end));
cachedVersionSent = true;
}
// In case our vendor servers are unresponsive.
@ -119,24 +131,39 @@ function cache(f) {
var serverResponsive = setTimeout(function() {
serverUnresponsive = true;
if (requestCache.has(cacheIndex)) {
var cached = requestCache.get(cacheIndex);
badge(cached.badgeData, makeSend(cached.format, ask.res, end));
var cached = requestCache.get(cacheIndex).data;
if (!cachedVersionSent) {
badge(cached.badgeData, makeSend(cached.format, ask.res, end));
}
return;
}
var badgeData = getBadgeData('vendor', data);
badgeData.text[1] = 'unresponsive';
badge(badgeData, makeSend('svg', ask.res, end));
if (!cachedVersionSent) {
badge(badgeData, makeSend('svg', ask.res, end));
}
}, 25000);
f(data, match, function sendBadge(format, badgeData) {
if (serverUnresponsive) { return; }
clearTimeout(serverResponsive);
cacheFromIndex[cacheIndex] = { format: format, badgeData: badgeData };
requestCache.set(cacheIndex, { format: format, badgeData: badgeData });
setTimeout(function clearCache() {
delete cacheFromIndex[cacheIndex];
}, cacheTimeout);
badge(badgeData, makeSend(format, ask.res, end));
// Check for a change in the data.
var dataHasChanged = false;
if (cached !== undefined
&& cached.data.badgeData.text[1] !== badgeData.text[1]) {
dataHasChanged = true;
}
// Update information in the cache.
var updatedCache = {
reqs: cached? (cached.reqs + 1): 1,
dataChange: cached? (cached.dataChange + (dataHasChanged? 1: 0))
: 1,
data: { format: format, badgeData: badgeData }
};
requestCache.set(cacheIndex, updatedCache);
if (!cachedVersionSent) {
badge(badgeData, makeSend(format, ask.res, end));
}
});
};
}