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Memory-Mapped I/O

Memory-Mapped I/O

The default mechanism by which SQLite accesses and updates database disk files is the xRead() and xWrite() methods of the sqlite3_io_methods VFS object. These methods are typically implemented as "read()" and "write()" system calls which cause the operating system to copy disk content between the kernel buffer cache and user space.

Beginning with version 3.7.17 (2013-05-20), SQLite has the option of accessing disk content directly using memory-mapped I/O and the new xFetch() and xUnfetch() methods on sqlite3_io_methods.

There are advantages and disadvantages to using memory-mapped I/O. Advantages include:

  1. Many operations, especially I/O intensive operations, can be faster since content does need to be copied between