Why does Chrome's cache max out at 638 MB?
August 27, 2016 7:10 PM   Subscribe

I periodically wipe Chrome's browsing data (usually when it starts feeling sluggish). The window that pops up shows the 'cached images and files' size. It's almost always at 638 MB and I've never seen it go higher. Why 638? Is it truthful? Is it arbitrary?
posted by cichlid ceilidh to Computers & Internet (4 answers total) 3 users marked this as a favorite
It may be capped at a percentage of your total disk space.
posted by mbrubeck at 8:00 PM on August 27, 2016

That's interesting, my Chrome cache is also capped at 638 MB.

I have a 2014 Macbook Pro Retina, 16GB DDR3, 500GB flash storage drive (405GB free).
posted by invisible ink at 9:39 PM on August 27, 2016

Response by poster: invisible ink, none of those specs match mine (2011 Macbook Pro, 4GB RAM, 318 GB storage with 142 GB free).
posted by cichlid ceilidh at 5:27 AM on August 28, 2016

Best answer: This is an interesting question, I never thought about it! My iMac with bazillions of disk space and browser usage also is 639MB. This has to be some global maximum. I did a bit of research.

This post from 2012 appears to be a Chromium developer talking about how the cache size maximum is 320MB. Using more disk did not improve performance.
Why do we cap at 320MB you ask? Well, during the Chrome beta, Ricardo ran a bunch of experiments with different cache sizes and found that beyond 320MB, the cache hit rate improvements were negligible, but the long tail of disk lookups started increasing, so performance actually degraded
So that explains why the cache has a limit. Not sure if 320MB is still the limit, it's possible they just doubled it to 640MB?

Except... if you open chrome://net-internals/#httpCache you'll see cache statistics. Mine has a current size of 334945927, or 319.4MB, even though when I clear the cache I'm told it's 639MB. But maybe there's a 320MB limit for "files" (being shown here) and another 320MB for images?

There's some official docs on setting cache sizes, but they don't describe what the defaults are. There are separate settings for DiskCacheSize and MediaCacheSize.
posted by Nelson at 7:33 AM on August 28, 2016 [1 favorite]

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