Merge 'set non-shared cache by default' from Pere Diaz Bou

Shared cache requires more locking mechasnisms. We still have multi
threading issues not related to shared cache so it is wise to first fix
those and then once they are fixed, we can incrementally add shared
cache back with locking in place.

Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>

Closes #1568

core/lib.rs

@@ -101,7 +101,7 @@ pub struct Database {
     page_size: u32,
     // Shared structures of a Database are the parts that are common to multiple threads that might
     // create DB connections.
-    shared_page_cache: Arc<RwLock<DumbLruPageCache>>,
+    _shared_page_cache: Arc<RwLock<DumbLruPageCache>>,
     shared_wal: Arc<UnsafeCell<WalFileShared>>,
     open_flags: OpenFlags,
 }
@@ -174,7 +174,7 @@ impl Database {
             mv_store,
             schema: schema.clone(),
             header: db_header.clone(),
-            shared_page_cache: shared_page_cache.clone(),
+            _shared_page_cache: shared_page_cache.clone(),
             shared_wal: shared_wal.clone(),
             db_file,
             io: io.clone(),
@@ -210,12 +210,13 @@ impl Database {
             self.shared_wal.clone(),
             buffer_pool.clone(),
         )));
+        // For now let's open database without shared cache by default.
         let pager = Rc::new(Pager::finish_open(
             self.header.clone(),
             self.db_file.clone(),
             Some(wal),
             self.io.clone(),
-            self.shared_page_cache.clone(),
+            Arc::new(RwLock::new(DumbLruPageCache::default())),
             buffer_pool,
         )?);
         let conn = Rc::new(Connection {
@@ -230,6 +231,7 @@ impl Database {
             last_change: Cell::new(0),
             syms: RefCell::new(SymbolTable::new()),
             total_changes: Cell::new(0),
+            _shared_cache: false,
         });
         if let Err(e) = conn.register_builtins() {
             return Err(LimboError::ExtensionError(e));
@@ -327,6 +329,7 @@ pub struct Connection {
     last_change: Cell<i64>,
     total_changes: Cell<i64>,
     syms: RefCell<SymbolTable>,
+    _shared_cache: bool,
 }
 
 impl Connection {