That's patently false. There are about 8 bn. people. Even if everyone has a smartphone or two, it's nothing compared to the total of all devices that can be called "computer". I think that "smart TV" alone will beat the number of smartphones. But even that is a drop in a bucket when it comes to the total of running programs on Earth / its orbit.
But, that's beside the point. Smartphones aren't designed to run database servers. Even if they indeed were the majority, they'd still be irrelevant for this conversation because they are a wrong platform for deploying databases. In other words, it doesn't matter how people deploy databases to smartphones -- they have no hopes of achieving good performance, and whether they use mmap or not is of no consequences -- they've lost the race before they even qualified for it.
> LMDB
Are we talking about this? https://en.wikipedia.org/wiki/Lightning_Memory-Mapped_Databa... If so, this is irrelevant for databases in general.
> LMDB databases may have only one writer at a time
(Taken from the page above) -- this isn't a serious contender for database server space. It's a toy database. You shouldn't give general advice based on whatever this system does or doesn't.
