In retrospect, I’d say it was something like 50% driven by Java memory mapping having insane issues on Windows, 20% Java memory mapping having insane issues on every platform, 25% me being a noob and 5% actual issues with memory mapping on Linux.
I think if could say “this DB is posix only” I would try memory mapping for the next DB I build
Great! Please reach out to us after you learn (again) that this is a bad idea!
At startup, it would read everything into memory so everything was hot, ready to go. The "database" was intended to run on a dedicated node with no other applications running. It also kept a write ahead log for transaction recovery.
I'm very interested, what issues? I've occasionally considered using mmap for a few things, but never had justification to. I'm curious what issues I might have run into.
Did you use JNI/JNA to mmap or via RandomAccessFile?
I've implemented a modest database in both C and Java with memory mapping. It's hard to explain the feeling of programming both but in general: with java I found myself trying to add intelligence at the cost of complexity to make things run faster. In C I could get speed by removing overheads and doing less work.