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    There are plenty of databases that use mmap. Some of them decided to not use anymore.

    Most of the “high profile” databases ignore mmap these days, or use it for limited purposes. For example, SQLite still uses mmap for shared memory between concurrent users of a single database file.

    Adjusting the memory map takes a write lock in Linux, making mmap prohibitively expensive for highly concurrent workloads. In one unfortunate but hilarious case, a colleague and I observed 100ms+ mmap latencies in production.