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Depends on your workload and whether incremental or not, Jukka measured 10-15% in #17955 (comment) , I've seen the lower end of that

It composes with sqlite, since mypy's sqlite thing just dumps json into sqlite. I think sqlite cache is mainly a way to workaround filesystem performance. I haven't benchmarked (or really used) the sqlite option. Jukka mentions he'd like to make it the default in the future though: #17955 (comment)