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One example: I personally used it to deduplicate recently viewed ads in an app, to avoid spamming users with the same ad too much. One interesting challenge there was that we needed to make sure that the client and server encode and decode the filter exactly the same, despite being implemented in different languages.

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Ooh that sounds fun.

Something I spent time thinking about, but wasn’t able to find a huge amount of information on, is how you could use compression alongside bloom filters. You could make enormous bloom filters that make use of run length encoding or sparse bitmaps. You sacrifice insert and lookup speed but you could make enormous bloom filters this way.

Bloom Filters are already lossy compression, so depending on how sparse they are I'm not sure you'll get too much benefit out of it, but maybe I'm just thinking of much, much smaller filters.

BTW we ended up open sourcing that BF library that encodes and decodes filters in multiple languages, the company has been out of business for nearly a decade but the project is still out there https://github.com/EverythingMe/inbloom

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