SQLite Forum

memory vs mmap
Great to hear you found the bottleneck. I admit that my test was not a very realistic in that it had a very high IO/CPU ratio. Just tried the one involving more or less the linear reading of the 100M file already in the system cache, the time of the disk db was almost as good as the equivalent one in the memory.   

An interesting side point. I found that :memory: databases indeed have some special treatment inside sqlite. My tweaking for VFS statistics never worked for memory databases. I suspected that I should just find a correct vfs. The one that jumped in the sources was "memdb", but actually it's another vfs-semantic memory database interface probably for serialization (available for finding only when sqlite is compiled with SQLITE_ENABLE_DESERIALIZE flag) and it looked like the bases opened with it works slower than native ":memory:" bases and even slower than memory-mapped disk bases (when the system already cached the data). I suppose this is an illustration of the phrase from the docs "Skipping the copy step is what makes memory mapped I/O faster". Probably ":memory:" databases are also able skip the copy step.