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This page describes a frecency measure based on exponential decay, and a way to store and update this measure efficiently. == Problems with the current old algorithm ==
https://developer.mozilla.org/en/The_Places_frecency_algorithm
That takes care of the buckets and sampling. It could be implemented by storing the URL frecency score, and having an idle-daily job that multiplies all scores by (e ^ (-(ln 2) / 30)) = 0.977.
== Efficient computation ==
But with an additional trick, ''no recomputation is necessary''. The trick is to store in the database something with units of date.
* Doesn't emulate the "slowing decay" of the current bucket weights.
** Could be emulated by having two exponential decays with different rates, if desired.
== Implementation ==
* Gecko - HTTP cache: [https://hg.mozilla.org/mozilla-central/file/b40296602083/netwerk/cache2/CacheEntry.cpp#l1497 in CacheEntry::BackgroundOp]
* Firefox - URL history: Still uses the old algorithm ([https://bugzilla.mozilla.org/show_bug.cgi?id=704025 bug 704025])
