https://sqlite.org/inmemorydb.html
"In-memory databases are allowed to use shared cache if they are opened using a URI filename. If the unadorned ":memory:" name is used to specify the in-memory database, then that database always has a private cache and is this only visible to the database connection that originally opened it. However, the same in-memory database can be opened by two or more database connections as follows:
rc = sqlite3_open("file::memory:?cache=shared", &db);
Or,
ATTACH DATABASE 'file::memory:?cache=shared' AS aux1;
This allows separate database connections to share the same in-memory database. Of course, all database connections sharing the in-memory database need to be in the same process. The database is automatically deleted and memory is reclaimed when the last connection to the database closes.
If two or more distinct but shareable in-memory databases are needed in a single process, then the mode=memory query parameter can be used with a URI filename to create a named in-memory database:
rc = sqlite3_open("file:memdb1?mode=memory&cache=shared", &db);
Or,
ATTACH DATABASE 'file:memdb1?mode=memory&cache=shared' AS aux1;
When an in-memory database is named in this way, it will only share its cache with another connection that uses exactly the same name."