sqlite3_release_memory —
Attempt To Free Heap Memory
int
sqlite3_release_memory(int);
The sqlite3_release_memory() interface attempts to free N bytes of heap memory
  by deallocating non-essential memory allocations held by the database library.
  Memory used to cache database pages to improve performance is an example of
  non-essential memory. sqlite3_release_memory() returns the number of bytes
  actually freed, which might be more or less than the amount requested. The
  sqlite3_release_memory() routine is a no-op returning zero if SQLite is not
  compiled with SQLITE_ENABLE_MEMORY_MANAGEMENT.