Loading adblock cache takes 2-4s with huge cache file

[The-Compiler]

Before I explain the issue, let me note that I'm not sure if this is the right place - chances are, the answer is just "don't do that...", or perhaps this is something that can be improved somehow in the adblocking library rather than this wrapper. However, I lack the Rust knowledge to properly report it there, and I'd like to hear your opinion on this first.

Apparently, there have been posts suggesting to add many more filter lists to qutebrowser, namely:

c.content.blocking.adblock.lists = [
    'https://raw.githubusercontent.com/uBlockOrigin/uAssets/master/filters/annoyances.txt',
    'https://raw.githubusercontent.com/uBlockOrigin/uAssets/master/filters/badlists.txt',
    'https://raw.githubusercontent.com/uBlockOrigin/uAssets/master/filters/badware.txt',
    'https://raw.githubusercontent.com/uBlockOrigin/uAssets/master/filters/filters-2020.txt',
    'https://raw.githubusercontent.com/uBlockOrigin/uAssets/master/filters/filters-2021.txt',
    'https://raw.githubusercontent.com/uBlockOrigin/uAssets/master/filters/filters.txt',
    'https://raw.githubusercontent.com/uBlockOrigin/uAssets/master/filters/privacy.txt',
    'https://raw.githubusercontent.com/uBlockOrigin/uAssets/master/filters/resource-abuse.txt',
    'https://raw.githubusercontent.com/uBlockOrigin/uAssets/master/thirdparties/easylist-downloads.adblockplus.org/easyprivacy.txt',
    'https://raw.githubusercontent.com/uBlockOrigin/uAssets/master/thirdparties/pgl.yoyo.org/as/serverlist',
    'https://raw.githubusercontent.com/StevenBlack/hosts/master/alternates/fakenews-gambling/hosts',
    'https://raw.githubusercontent.com/AdAway/adaway.github.io/master/hosts.txt',
    'https://fanboy.co.nz/fanboy-problematic-sites.txt',
    'https://easylist.to/easylist/easylist.txt',
    'https://raw.githubusercontent.com/bogachenko/fuckfuckadblock/master/fuckfuckadblock.txt'
]

It looks like there are people who blindly copy that, because more clearly must be better or something...

However, running :adblock-update with those lists results in a adblock-cache.dat which is around 130 MB, and qutebrowser hangs about 2-4s at startup with it (when calling self._engine.deserialize_from_file). Some questions/ideas:

• Is it really supposed to be that large (i.e. are there really so many unique filters in those lists)?
• Do we also save things like cosmetic filters and such, despite not supporting them yet? If so, would it help to filter (hah) them out?
• Should it really take 2-4s to deserialize? Can the Brave library maybe improve its performance somehow there?
• Maybe qutebrowser should just detect when deserialization takes more than 1s or so and warn about it?

[ArniDagur]

Do you know if the performance has always been this bad for large blocklists, or if it only started happening after the recent 5.2 update? In the latter case, I may have an inkling of what is wrong.

[The-Compiler]

Looks like it takes a similar time on 0.5.0 too for me.

[ArniDagur]

Ah, I think I know why. The underlying adblock library used to compress the cache file with brotli, but doesn't do that anymore. I guess I should fix that by compressing with brotli in python-adblock. Alternatively, qutebrowser could use serialize (as opposed to serialize_to_file), and do its own compression using zlib.

[The-Compiler]

Both would be fine by me. Though from reading brave/adblock-rust@85063aa (which was then reverted in brave/adblock-rust@d61c0e5 it should still be doing gzip compression, no?