bpo-42862: Use functools.lru_cache iso. _sqlite.Cache in sqlite3 module (GH-24203)

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>

Doc/library/sqlite3.rst

@@ -213,7 +213,7 @@ Module functions and constants
    The :mod:`sqlite3` module internally uses a statement cache to avoid SQL parsing
    overhead. If you want to explicitly set the number of statements that are cached
    for the connection, you can set the *cached_statements* parameter. The currently
-   implemented default is to cache 100 statements.
+   implemented default is to cache 128 statements.
 
    If *uri* is true, *database* is interpreted as a URI. This allows you
    to specify options. For example, to open a database in read-only mode

Misc/NEWS.d/next/Library/2021-01-13-00-02-44.bpo-42862.Z6ACLN.rst

@@ -0,0 +1,4 @@
+:mod:`sqlite3` now utilizes :meth:`functools.lru_cache` to implement the
+connection statement cache. As a small optimisation, the default
+statement cache size has been increased from 100 to 128.
+Patch by Erlend E. Aasland.

Modules/_sqlite/cache.c

@@ -1,344 +0,0 @@
-/* cache .c - a LRU cache
- *
- * Copyright (C) 2004-2010 Gerhard Häring <gh@ghaering.de>
- *
- * This file is part of pysqlite.
- *
- * This software is provided 'as-is', without any express or implied
- * warranty.  In no event will the authors be held liable for any damages
- * arising from the use of this software.
- *
- * Permission is granted to anyone to use this software for any purpose,
- * including commercial applications, and to alter it and redistribute it
- * freely, subject to the following restrictions:
- *
- * 1. The origin of this software must not be misrepresented; you must not
- *    claim that you wrote the original software. If you use this software
- *    in a product, an acknowledgment in the product documentation would be
- *    appreciated but is not required.
- * 2. Altered source versions must be plainly marked as such, and must not be
- *    misrepresented as being the original software.
- * 3. This notice may not be removed or altered from any source distribution.
- */
-
-#include "cache.h"
-#include <limits.h>
-
-/* only used internally */
-static pysqlite_Node *
-pysqlite_new_node(PyObject *key, PyObject *data)
-{
-    pysqlite_Node* node;
-
-    node = (pysqlite_Node*) (pysqlite_NodeType->tp_alloc(pysqlite_NodeType, 0));
-    if (!node) {
-        return NULL;
-    }
-
-    node->key = Py_NewRef(key);
-    node->data = Py_NewRef(data);
-
-    node->prev = NULL;
-    node->next = NULL;
-
-    return node;
-}
-
-static int
-node_traverse(pysqlite_Node *self, visitproc visit, void *arg)
-{
-    Py_VISIT(Py_TYPE(self));
-    Py_VISIT(self->key);
-    Py_VISIT(self->data);
-    return 0;
-}
-
-static int
-node_clear(pysqlite_Node *self)
-{
-    Py_CLEAR(self->key);
-    Py_CLEAR(self->data);
-    return 0;
-}
-
-static void
-pysqlite_node_dealloc(pysqlite_Node *self)
-{
-    PyTypeObject *tp = Py_TYPE(self);
-    PyObject_GC_UnTrack(self);
-    tp->tp_clear((PyObject *)self);
-    tp->tp_free(self);
-    Py_DECREF(tp);
-}
-
-static int
-pysqlite_cache_init(pysqlite_Cache *self, PyObject *args, PyObject *kwargs)
-{
-    PyObject* factory;
-    int size = 10;
-
-    self->factory = NULL;
-
-    if (!PyArg_ParseTuple(args, "O|i", &factory, &size)) {
-        return -1;
-    }
-
-    /* minimum cache size is 5 entries */
-    if (size < 5) {
-        size = 5;
-    }
-    self->size = size;
-    self->first = NULL;
-    self->last = NULL;
-
-    self->mapping = PyDict_New();
-    if (!self->mapping) {
-        return -1;
-    }
-
-    self->factory = Py_NewRef(factory);
-    return 0;
-}
-
-static int
-cache_traverse(pysqlite_Cache *self, visitproc visit, void *arg)
-{
-    Py_VISIT(Py_TYPE(self));
-    Py_VISIT(self->mapping);
-    Py_VISIT(self->factory);
-
-    pysqlite_Node *node = self->first;
-    while (node) {
-        Py_VISIT(node);
-        node = node->next;
-    }
-    return 0;
-}
-
-static int
-cache_clear(pysqlite_Cache *self)
-{
-    Py_CLEAR(self->mapping);
-    Py_CLEAR(self->factory);
-
-    /* iterate over all nodes and deallocate them */
-    pysqlite_Node *node = self->first;
-    self->first = NULL;
-    while (node) {
-        pysqlite_Node *delete_node = node;
-        node = node->next;
-        Py_CLEAR(delete_node);
-    }
-    return 0;
-}
-
-static void
-pysqlite_cache_dealloc(pysqlite_Cache *self)
-{
-    if (!self->factory) {
-        /* constructor failed, just get out of here */
-        return;
-    }
-
-    PyObject_GC_UnTrack(self);
-    PyTypeObject *tp = Py_TYPE(self);
-    tp->tp_clear((PyObject *)self);
-    tp->tp_free(self);
-    Py_DECREF(tp);
-}
-
-PyObject* pysqlite_cache_get(pysqlite_Cache* self, PyObject* key)
-{
-    pysqlite_Node* node;
-    pysqlite_Node* ptr;
-    PyObject* data;
-
-    node = (pysqlite_Node*)PyDict_GetItemWithError(self->mapping, key);
-    if (node) {
-        /* an entry for this key already exists in the cache */
-
-        /* increase usage counter of the node found */
-        if (node->count < LONG_MAX) {
-            node->count++;
-        }
-
-        /* if necessary, reorder entries in the cache by swapping positions */
-        if (node->prev && node->count > node->prev->count) {
-            ptr = node->prev;
-
-            while (ptr->prev && node->count > ptr->prev->count) {
-                ptr = ptr->prev;
-            }
-
-            if (node->next) {
-                node->next->prev = node->prev;
-            } else {
-                self->last = node->prev;
-            }
-            if (node->prev) {
-                node->prev->next = node->next;
-            }
-            if (ptr->prev) {
-                ptr->prev->next = node;
-            } else {
-                self->first = node;
-            }
-
-            node->next = ptr;
-            node->prev = ptr->prev;
-            if (!node->prev) {
-                self->first = node;
-            }
-            ptr->prev = node;
-        }
-    }
-    else if (PyErr_Occurred()) {
-        return NULL;
-    }
-    else {
-        /* There is no entry for this key in the cache, yet. We'll insert a new
-         * entry in the cache, and make space if necessary by throwing the
-         * least used item out of the cache. */
-
-        if (PyDict_GET_SIZE(self->mapping) == self->size) {
-            if (self->last) {
-                node = self->last;
-
-                if (PyDict_DelItem(self->mapping, self->last->key) != 0) {
-                    return NULL;
-                }
-
-                if (node->prev) {
-                    node->prev->next = NULL;
-                }
-                self->last = node->prev;
-                node->prev = NULL;
-
-                Py_DECREF(node);
-            }
-        }
-
-        /* We cannot replace this by PyObject_CallOneArg() since
-         * PyObject_CallFunction() has a special case when using a
-         * single tuple as argument. */
-        data = PyObject_CallFunction(self->factory, "O", key);
-
-        if (!data) {
-            return NULL;
-        }
-
-        node = pysqlite_new_node(key, data);
-        if (!node) {
-            return NULL;
-        }
-        node->prev = self->last;
-
-        Py_DECREF(data);
-
-        if (PyDict_SetItem(self->mapping, key, (PyObject*)node) != 0) {
-            Py_DECREF(node);
-            return NULL;
-        }
-
-        if (self->last) {
-            self->last->next = node;
-        } else {
-            self->first = node;
-        }
-        self->last = node;
-    }
-
-    return Py_NewRef(node->data);
-}
-
-static PyObject *
-pysqlite_cache_display(pysqlite_Cache *self, PyObject *args)
-{
-    pysqlite_Node* ptr;
-    PyObject* prevkey;
-    PyObject* nextkey;
-    PyObject* display_str;
-
-    ptr = self->first;
-
-    while (ptr) {
-        if (ptr->prev) {
-            prevkey = ptr->prev->key;
-        } else {
-            prevkey = Py_None;
-        }
-
-        if (ptr->next) {
-            nextkey = ptr->next->key;
-        } else {
-            nextkey = Py_None;
-        }
-
-        display_str = PyUnicode_FromFormat("%S <- %S -> %S\n",
-                                           prevkey, ptr->key, nextkey);
-        if (!display_str) {
-            return NULL;
-        }
-        PyObject_Print(display_str, stdout, Py_PRINT_RAW);
-        Py_DECREF(display_str);
-
-        ptr = ptr->next;
-    }
-
-    Py_RETURN_NONE;
-}
-
-static PyType_Slot node_slots[] = {
-    {Py_tp_dealloc, pysqlite_node_dealloc},
-    {Py_tp_traverse, node_traverse},
-    {Py_tp_clear, node_clear},
-    {0, NULL},
-};
-
-static PyType_Spec node_spec = {
-    .name = MODULE_NAME ".Node",
-    .basicsize = sizeof(pysqlite_Node),
-    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,
-    .slots = node_slots,
-};
-PyTypeObject *pysqlite_NodeType = NULL;
-
-static PyMethodDef cache_methods[] = {
-    {"get", (PyCFunction)pysqlite_cache_get, METH_O,
-        PyDoc_STR("Gets an entry from the cache or calls the factory function to produce one.")},
-    {"display", (PyCFunction)pysqlite_cache_display, METH_NOARGS,
-        PyDoc_STR("For debugging only.")},
-    {NULL, NULL}
-};
-
-static PyType_Slot cache_slots[] = {
-    {Py_tp_dealloc, pysqlite_cache_dealloc},
-    {Py_tp_methods, cache_methods},
-    {Py_tp_init, pysqlite_cache_init},
-    {Py_tp_traverse, cache_traverse},
-    {Py_tp_clear, cache_clear},
-    {0, NULL},
-};
-
-static PyType_Spec cache_spec = {
-    .name = MODULE_NAME ".Cache",
-    .basicsize = sizeof(pysqlite_Cache),
-    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,
-    .slots = cache_slots,
-};
-PyTypeObject *pysqlite_CacheType = NULL;
-
-int
-pysqlite_cache_setup_types(PyObject *mod)
-{
-    pysqlite_NodeType = (PyTypeObject *)PyType_FromModuleAndSpec(mod, &node_spec, NULL);
-    if (pysqlite_NodeType == NULL) {
-        return -1;
-    }
-
-    pysqlite_CacheType = (PyTypeObject *)PyType_FromModuleAndSpec(mod, &cache_spec, NULL);
-    if (pysqlite_CacheType == NULL) {
-        return -1;
-    }
-    return 0;
-}

Modules/_sqlite/cache.h

@@ -1,64 +0,0 @@
-/* cache.h - definitions for the LRU cache
- *
- * Copyright (C) 2004-2010 Gerhard Häring <gh@ghaering.de>
- *
- * This file is part of pysqlite.
- *
- * This software is provided 'as-is', without any express or implied
- * warranty.  In no event will the authors be held liable for any damages
- * arising from the use of this software.
- *
- * Permission is granted to anyone to use this software for any purpose,
- * including commercial applications, and to alter it and redistribute it
- * freely, subject to the following restrictions:
- *
- * 1. The origin of this software must not be misrepresented; you must not
- *    claim that you wrote the original software. If you use this software
- *    in a product, an acknowledgment in the product documentation would be
- *    appreciated but is not required.
- * 2. Altered source versions must be plainly marked as such, and must not be
- *    misrepresented as being the original software.
- * 3. This notice may not be removed or altered from any source distribution.
- */
-
-#ifndef PYSQLITE_CACHE_H
-#define PYSQLITE_CACHE_H
-#include "module.h"
-
-/* The LRU cache is implemented as a combination of a doubly-linked with a
- * dictionary. The list items are of type 'Node' and the dictionary has the
- * nodes as values. */
-
-typedef struct _pysqlite_Node
-{
-    PyObject_HEAD
-    PyObject* key;
-    PyObject* data;
-    long count;
-    struct _pysqlite_Node* prev;
-    struct _pysqlite_Node* next;
-} pysqlite_Node;
-
-typedef struct
-{
-    PyObject_HEAD
-    int size;
-
-    /* a dictionary mapping keys to Node entries */
-    PyObject* mapping;
-
-    /* the factory callable */
-    PyObject* factory;
-
-    pysqlite_Node* first;
-    pysqlite_Node* last;
-} pysqlite_Cache;
-
-extern PyTypeObject *pysqlite_NodeType;
-extern PyTypeObject *pysqlite_CacheType;
-
-PyObject* pysqlite_cache_get(pysqlite_Cache* self, PyObject* args);
-
-int pysqlite_cache_setup_types(PyObject *module);
-
-#endif

Modules/_sqlite/connection.c

@@ -21,7 +21,6 @@
  * 3. This notice may not be removed or altered from any source distribution.
  */
 
-#include "cache.h"
 #include "module.h"
 #include "structmember.h"         // PyMemberDef
 #include "connection.h"
@@ -57,6 +56,26 @@ static const char * const begin_statements[] = {
 static int pysqlite_connection_set_isolation_level(pysqlite_Connection* self, PyObject* isolation_level, void *Py_UNUSED(ignored));
 static void _pysqlite_drop_unused_cursor_references(pysqlite_Connection* self);
 
+static PyObject *
+new_statement_cache(pysqlite_Connection *self, int maxsize)
+{
+    PyObject *args[] = { PyLong_FromLong(maxsize), };
+    if (args[0] == NULL) {
+        return NULL;
+    }
+    pysqlite_state *state = pysqlite_get_state(NULL);
+    PyObject *inner = PyObject_Vectorcall(state->lru_cache, args, 1, NULL);
+    Py_DECREF(args[0]);
+    if (inner == NULL) {
+        return NULL;
+    }
+
+    args[0] = (PyObject *)self;  // Borrowed ref.
+    PyObject *res = PyObject_Vectorcall(inner, args, 1, NULL);
+    Py_DECREF(inner);
+    return res;
+}
+
 static int
 pysqlite_connection_init(pysqlite_Connection *self, PyObject *args,
                          PyObject *kwargs)
@@ -73,7 +92,7 @@ pysqlite_connection_init(pysqlite_Connection *self, PyObject *args,
     PyObject* isolation_level = NULL;
     PyObject* factory = NULL;
     int check_same_thread = 1;
-    int cached_statements = 100;
+    int cached_statements = 128;
     int uri = 0;
     double timeout = 5.0;
     int rc;
@@ -134,7 +153,10 @@ pysqlite_connection_init(pysqlite_Connection *self, PyObject *args,
     }
     Py_DECREF(isolation_level);
 
-    self->statement_cache = (pysqlite_Cache*)PyObject_CallFunction((PyObject*)pysqlite_CacheType, "Oi", self, cached_statements);
+    self->statement_cache = new_statement_cache(self, cached_statements);
+    if (self->statement_cache == NULL) {
+        return -1;
+    }
     if (PyErr_Occurred()) {
         return -1;
     }

Modules/_sqlite/connection.h

@@ -28,7 +28,6 @@
 #include "pythread.h"
 #include "structmember.h"
 
-#include "cache.h"
 #include "module.h"
 
 #include "sqlite3.h"
@@ -64,7 +63,7 @@ typedef struct
     /* thread identification of the thread the connection was created in */
     unsigned long thread_ident;
 
-    pysqlite_Cache* statement_cache;
+    PyObject *statement_cache;
 
     /* Lists of weak references to statements and cursors used within this connection */
     PyObject* statements;

Modules/_sqlite/cursor.c

@@ -415,6 +415,14 @@ static int check_cursor(pysqlite_Cursor* cur)
     return pysqlite_check_thread(cur->connection) && pysqlite_check_connection(cur->connection);
 }
 
+static PyObject *
+get_statement_from_cache(pysqlite_Cursor *self, PyObject *operation)
+{
+    PyObject *args[] = { operation, };
+    PyObject *cache = self->connection->statement_cache;
+    return PyObject_Vectorcall(cache, args, 1, NULL);
+}
+
 static PyObject *
 _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* operation, PyObject* second_argument)
 {
@@ -423,7 +431,6 @@ _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* operation
     PyObject* parameters = NULL;
     int i;
     int rc;
-    PyObject* func_args;
     PyObject* result;
     int numcols;
     PyObject* column_name;
@@ -485,22 +492,12 @@ _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* operation
     Py_SETREF(self->description, Py_None);
     self->rowcount = 0L;
 
-    func_args = PyTuple_New(1);
-    if (!func_args) {
-        goto error;
-    }
-    if (PyTuple_SetItem(func_args, 0, Py_NewRef(operation)) != 0) {
-        goto error;
-    }
-
     if (self->statement) {
         (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);
-
+    PyObject *stmt = get_statement_from_cache(self, operation);
+    Py_XSETREF(self->statement, (pysqlite_Statement *)stmt);
     if (!self->statement) {
         goto error;
     }

Modules/_sqlite/module.c

@@ -24,7 +24,6 @@
 #include "connection.h"
 #include "statement.h"
 #include "cursor.h"
-#include "cache.h"
 #include "prepare_protocol.h"
 #include "microprotocols.h"
 #include "row.h"
@@ -56,6 +55,14 @@ PyObject* _pysqlite_converters = NULL;
 int _pysqlite_enable_callback_tracebacks = 0;
 int pysqlite_BaseTypeAdapted = 0;
 
+pysqlite_state pysqlite_global_state;
+
+pysqlite_state *
+pysqlite_get_state(PyObject *Py_UNUSED(module))
+{
+    return &pysqlite_global_state;
+}
+
 static PyObject* module_connect(PyObject* self, PyObject* args, PyObject*
         kwargs)
 {
@@ -261,6 +268,23 @@ static int converters_init(PyObject* module)
     return res;
 }
 
+static int
+load_functools_lru_cache(PyObject *module)
+{
+    PyObject *functools = PyImport_ImportModule("functools");
+    if (functools == NULL) {
+        return -1;
+    }
+
+    pysqlite_state *state = pysqlite_get_state(module);
+    state->lru_cache = PyObject_GetAttrString(functools, "lru_cache");
+    Py_DECREF(functools);
+    if (state->lru_cache == NULL) {
+        return -1;
+    }
+    return 0;
+}
+
 static PyMethodDef module_methods[] = {
     {"connect",  (PyCFunction)(void(*)(void))module_connect,
      METH_VARARGS | METH_KEYWORDS, module_connect_doc},
@@ -373,7 +397,6 @@ PyMODINIT_FUNC PyInit__sqlite3(void)
         (pysqlite_row_setup_types(module) < 0) ||
         (pysqlite_cursor_setup_types(module) < 0) ||
         (pysqlite_connection_setup_types(module) < 0) ||
-        (pysqlite_cache_setup_types(module) < 0) ||
         (pysqlite_statement_setup_types(module) < 0) ||
         (pysqlite_prepare_protocol_setup_types(module) < 0)
        ) {
@@ -424,6 +447,10 @@ PyMODINIT_FUNC PyInit__sqlite3(void)
         goto error;
     }
 
+    if (load_functools_lru_cache(module) < 0) {
+        goto error;
+    }
+
     return module;
 
 error:

Modules/_sqlite/module.h

@@ -29,6 +29,12 @@
 #define PYSQLITE_VERSION "2.6.0"
 #define MODULE_NAME "sqlite3"
 
+typedef struct {
+    PyObject *lru_cache;
+} pysqlite_state;
+
+extern pysqlite_state *pysqlite_get_state(PyObject *module);
+
 extern PyObject* pysqlite_Error;
 extern PyObject* pysqlite_Warning;
 extern PyObject* pysqlite_InterfaceError;

PCbuild/_sqlite3.vcxproj

@@ -97,7 +97,6 @@
     </ClCompile>
   </ItemDefinitionGroup>
   <ItemGroup>
-    <ClInclude Include="..\Modules\_sqlite\cache.h" />
     <ClInclude Include="..\Modules\_sqlite\connection.h" />
     <ClInclude Include="..\Modules\_sqlite\cursor.h" />
     <ClInclude Include="..\Modules\_sqlite\microprotocols.h" />
@@ -108,7 +107,6 @@
     <ClInclude Include="..\Modules\_sqlite\util.h" />
   </ItemGroup>
   <ItemGroup>
-    <ClCompile Include="..\Modules\_sqlite\cache.c" />
     <ClCompile Include="..\Modules\_sqlite\connection.c" />
     <ClCompile Include="..\Modules\_sqlite\cursor.c" />
     <ClCompile Include="..\Modules\_sqlite\microprotocols.c" />

PCbuild/_sqlite3.vcxproj.filters

@@ -12,9 +12,6 @@
     </Filter>
   </ItemGroup>
   <ItemGroup>
-    <ClInclude Include="..\Modules\_sqlite\cache.h">
-      <Filter>Header Files</Filter>
-    </ClInclude>
     <ClInclude Include="..\Modules\_sqlite\connection.h">
       <Filter>Header Files</Filter>
     </ClInclude>
@@ -41,9 +38,6 @@
     </ClInclude>
   </ItemGroup>
   <ItemGroup>
-    <ClCompile Include="..\Modules\_sqlite\cache.c">
-      <Filter>Source Files</Filter>
-    </ClCompile>
     <ClCompile Include="..\Modules\_sqlite\connection.c">
       <Filter>Source Files</Filter>
     </ClCompile>

setup.py

@@ -1578,7 +1578,7 @@ class PyBuildExt(build_ext):
                 sqlite_libdir = [os.path.abspath(os.path.dirname(sqlite_libfile))]
 
         if sqlite_incdir and sqlite_libdir:
-            sqlite_srcs = ['_sqlite/cache.c',
+            sqlite_srcs = [
                 '_sqlite/connection.c',
                 '_sqlite/cursor.c',
                 '_sqlite/microprotocols.c',