This paper discusses the use of memory-mapped (MMAP) file I/O in database management systems (DBMS). MMAP allows files on secondary storage to be accessed as if they were entirely in memory, with the operating system handling the loading and eviction of pages. While MMAP has been a popular choice for managing large databases, there are significant issues with correctness and performance that aren’t immediately apparent. Many DBMSs have encountered these problems and have had to switch to managing file I/O themselves. The paper warns against using MMAP as a replacement for a traditional buffer pool and provides a prescription for when it might be suitable.
https://db.cs.cmu.edu/mmap-cidr2022/