bpo-30271: Make sqlite3 statement cache optional

Doc/library/sqlite3.rst

@@ -223,6 +223,9 @@ Module functions and constants
    .. versionchanged:: 3.4
       Added the *uri* parameter.
 
+   .. versionchanged:: 3.7
+      When *cached_statements* is set to 0 there is no statement cache.
+
 
 .. function:: register_converter(typename, callable)
 

Misc/NEWS

@@ -10,6 +10,8 @@ What's New in Python 3.7.0 alpha 1?
 Core and Builtins
 -----------------
 
+- bpo-30271: sqlite3 statement cache is optional.  Patch by Aviv Palivoda.
+
 - bpo-12414: sys.getsizeof() on a code object now returns the sizes
   which includes the code struct and sizes of objects which it references.
   Patch by Dong-hee Na.

Modules/_sqlite/cache.c

@@ -65,9 +65,11 @@ int pysqlite_cache_init(pysqlite_Cache* self, PyObject* args, PyObject* kwargs)
         return -1;
     }
 
-    /* minimum cache size is 5 entries */
-    if (size < 5) {
-        size = 5;
+    /* minimum cache size is 1 entry */
+    if (size < 1) {
+        PyErr_SetString(PyExc_ValueError,
+                        "Minimum cache size is 1");
+        return -1;
     }
     self->size = size;
     self->first = NULL;

Modules/_sqlite/connection.c

@@ -144,9 +144,18 @@ int pysqlite_connection_init(pysqlite_Connection* self, PyObject* args, PyObject
     }
     Py_DECREF(isolation_level);
 
-    self->statement_cache = (pysqlite_Cache*)PyObject_CallFunction((PyObject*)&pysqlite_CacheType, "Oi", self, cached_statements);
-    if (PyErr_Occurred()) {
-        return -1;
+    if (cached_statements != 0) {
+        self->statement_cache = (pysqlite_Cache*)PyObject_CallFunction((PyObject*)&pysqlite_CacheType, "Oi", self, cached_statements);
+        if (PyErr_Occurred()) {
+            return -1;
+        }
+        /* By default, the Cache class INCREFs the factory in its initializer, and
+         * decrefs it in its deallocator method. Since this would create a circular
+         * reference here, we're breaking it by decrementing self, and telling the
+         * cache class to not decref the factory (self) in its deallocator.
+         */
+        self->statement_cache->decref_factory = 0;
+        Py_DECREF(self);
     }
 
     self->created_statements = 0;
@@ -159,14 +168,6 @@ int pysqlite_connection_init(pysqlite_Connection* self, PyObject* args, PyObject
         return -1;
     }
 
-    /* By default, the Cache class INCREFs the factory in its initializer, and
-     * decrefs it in its deallocator method. Since this would create a circular
-     * reference here, we're breaking it by decrementing self, and telling the
-     * cache class to not decref the factory (self) in its deallocator.
-     */
-    self->statement_cache->decref_factory = 0;
-    Py_DECREF(self);
-
     self->detect_types = detect_types;
     self->timeout = timeout;
     (void)sqlite3_busy_timeout(self->db, (int)(timeout*1000));
@@ -238,7 +239,9 @@ void pysqlite_do_all_statements(pysqlite_Connection* self, int action, int reset
 
 void pysqlite_connection_dealloc(pysqlite_Connection* self)
 {
-    Py_XDECREF(self->statement_cache);
+    if (self->statement_cache) {
+        Py_XDECREF(self->statement_cache);
+    }
 
     /* Clean up if user has not called .close() explicitly. */
     if (self->db) {

Modules/_sqlite/cursor.c

@@ -487,9 +487,16 @@ PyObject* _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject*
         (void)pysqlite_statement_reset(self->statement);
     }
 
-    Py_XSETREF(self->statement,
-              (pysqlite_Statement *)pysqlite_cache_get(self->connection->statement_cache, func_args));
-    Py_DECREF(func_args);
+    if (self->connection->statement_cache) {
+        /* We look in statment cache */
+        Py_XSETREF(self->statement,
+                  (pysqlite_Statement *)pysqlite_cache_get(self->connection->statement_cache, func_args));
+        Py_DECREF(func_args);
+    } else {
+        /* We don't have statment cache */
+        Py_XSETREF(self->statement,
+                  (pysqlite_Statement *)PyObject_CallFunction((PyObject*)self->connection, "O", func_args));
+    }
 
     if (!self->statement) {
         goto error;