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bpo-44976: Lazy creation of sqlite3 result rows #27884

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Merged
pablogsal merged 1 commit into from
Aug 25, 2021
Merged

bpo-44976: Lazy creation of sqlite3 result rows #27884

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Only build result rows when needed 
- remove 'next_row' member in Cursor object
- remove fetch-one-row call from query execute loop
- rewrite cursor iternext method to comply with the new behaviour
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Erlend E. Aasland committed Aug 22, 2021
commit ce0d55fc55bd72e66f889e2e0d66f2e061102ab6
84 changes: 29 additions & 55 deletions Modules/_sqlite/cursor.c
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Original file line number Diff line number Diff line change
Expand Up @@ -53,7 +53,6 @@ pysqlite_cursor_init_impl(pysqlite_Cursor *self,
Py_INCREF(connection);
Py_XSETREF(self->connection, connection);
Py_CLEAR(self->statement);
Py_CLEAR(self->next_row);
Py_CLEAR(self->row_cast_map);

Py_INCREF(Py_None);
Expand Down Expand Up @@ -94,7 +93,6 @@ cursor_traverse(pysqlite_Cursor *self, visitproc visit, void *arg)
Py_VISIT(self->lastrowid);
Py_VISIT(self->row_factory);
Py_VISIT(self->statement);
Py_VISIT(self->next_row);
return 0;
}

Expand All @@ -111,7 +109,6 @@ cursor_clear(pysqlite_Cursor *self)
pysqlite_statement_reset(self->statement);
Py_CLEAR(self->statement);
}
Py_CLEAR(self->next_row);

return 0;
}
Expand Down Expand Up @@ -489,8 +486,6 @@ _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* operation
self->locked = 1;
self->reset = 0;

Py_CLEAR(self->next_row);

if (multiple) {
if (PyIter_Check(second_argument)) {
/* iterator */
Expand Down Expand Up @@ -658,11 +653,7 @@ _pysqlite_query_execute(pysqlite_Cursor* self, int multiple, PyObject* operation
}
}

if (rc == SQLITE_ROW) {
self->next_row = _pysqlite_fetch_one_row(self);
if (self->next_row == NULL)
goto error;
} else if (rc == SQLITE_DONE && !multiple) {
if (rc == SQLITE_DONE && !multiple) {
pysqlite_statement_reset(self->statement);
Py_CLEAR(self->statement);
}
Expand Down Expand Up @@ -821,10 +812,6 @@ pysqlite_cursor_executescript_impl(pysqlite_Cursor *self,
static PyObject *
pysqlite_cursor_iternext(pysqlite_Cursor *self)
{
PyObject* next_row_tuple;
PyObject* next_row;
int rc;

if (!check_cursor(self)) {
return NULL;
}
Expand All @@ -835,53 +822,40 @@ pysqlite_cursor_iternext(pysqlite_Cursor *self)
return NULL;
}

if (!self->next_row) {
if (self->statement) {
(void)pysqlite_statement_reset(self->statement);
Py_CLEAR(self->statement);
}
if (self->statement == NULL) {
return NULL;
}

next_row_tuple = self->next_row;
assert(next_row_tuple != NULL);
self->next_row = NULL;

if (self->row_factory != Py_None) {
next_row = PyObject_CallFunction(self->row_factory, "OO", self, next_row_tuple);
if (next_row == NULL) {
self->next_row = next_row_tuple;
return NULL;
}
Py_DECREF(next_row_tuple);
} else {
next_row = next_row_tuple;
sqlite3_stmt *stmt = self->statement->st;
assert(stmt != NULL);
if (sqlite3_data_count(stmt) == 0) {
(void)pysqlite_statement_reset(self->statement);
Py_CLEAR(self->statement);
return NULL;
}

if (self->statement) {
rc = pysqlite_step(self->statement->st);
if (PyErr_Occurred()) {
(void)pysqlite_statement_reset(self->statement);
Py_DECREF(next_row);
return NULL;
}
if (rc != SQLITE_DONE && rc != SQLITE_ROW) {
(void)pysqlite_statement_reset(self->statement);
Py_DECREF(next_row);
_pysqlite_seterror(self->connection->state, self->connection->db);
return NULL;
}

if (rc == SQLITE_ROW) {
self->next_row = _pysqlite_fetch_one_row(self);
if (self->next_row == NULL) {
(void)pysqlite_statement_reset(self->statement);
return NULL;
}
}
PyObject *row = _pysqlite_fetch_one_row(self);
if (row == NULL) {
return NULL;
}

return next_row;
int rc = pysqlite_step(stmt);
if (rc == SQLITE_DONE) {
(void)pysqlite_statement_reset(self->statement);
}
else if (rc != SQLITE_ROW) {
(void)_pysqlite_seterror(self->connection->state,
self->connection->db);
Py_DECREF(row);
return NULL;
}
if (!Py_IsNone(self->row_factory)) {
PyObject *factory = self->row_factory;
PyObject *args[] = { (PyObject *)self, row, };
PyObject *new_row = PyObject_Vectorcall(factory, args, 2, NULL);
Py_DECREF(row);
row = new_row;
}
return row;
}

/*[clinic input]
Expand Down
3 changes: 0 additions & 3 deletions Modules/_sqlite/cursor.h
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Original file line number Diff line number Diff line change
Expand Up @@ -46,9 +46,6 @@ typedef struct
int locked;
int initialized;

/* the next row to be returned, NULL if no next row available */
PyObject* next_row;

PyObject* in_weakreflist; /* List of weak references */
} pysqlite_Cursor;

Expand Down