Often, PRAGMA are documented like mmap_size, like: > Query or change the maximum number of bytes that are set aside > for memory-mapped I/O on a single database. The first > form (without an argument) queries the current limit. The > second form (with a numeric argument) sets the limit for the > specified database, or for all databases if the optional > database name is omitted.
I notice that mmap_size _also_ returns the set value, which is useful to query since it could be constrained by compile-time options or sqlite3_config settings. Like: sqlite> pragma mmap_size = 3221225472; -- 3GB 2147418112 -- 2GB - 64KB Sometimes pragma don't do this: sqlite> pragma auto_vacuum = 1; sqlite> pragma auto_vacuum; 1 Might it be useful to have a general policy that all PRAGMA calls return a result consistent with the first form, even if an argument is passed? As things currently stand, you really shouldn't depend on behavior like mmap_size's current implementation to do set-and-query, but you also can't write code as if setting pragma do not return results. -scott
