Commit 75430be8 authored by Marten Kenbeek's avatar Marten Kenbeek Committed by Markus Holtermann
Browse files

Refs #24366 -- Fixed recursion depth error in migration graph 

Made MigrationGraph forwards_plan() and backwards_plan() fall back to an
iterative approach in case the recursive approach exceeds the recursion
depth limit.
parent bc83add0

django/db/migrations/graph.py

+43 −2
Original line number Diff line number Diff line 
from __future__ import unicode_literals



import warnings

from collections import deque



from django.db.migrations.state import ProjectState
@@ -7,6 +8,13 @@ from django.utils.datastructures import OrderedSet 
from django.utils.encoding import python_2_unicode_compatible

from django.utils.functional import total_ordering



RECURSION_DEPTH_WARNING = (

    "Maximum recursion depth exceeded while generating migration graph, "

    "falling back to iterative approach. If you're experiencing performance issues, "

    "consider squashing migrations as described at "

    "https://docs.djangoproject.com/en/dev/topics/migrations/#squashing-migrations."

)





@python_2_unicode_compatible

@total_ordering
@@ -139,7 +147,12 @@ class MigrationGraph(object): 
        self.ensure_not_cyclic(target, lambda x: (parent.key for parent in self.node_map[x].parents))

        self.cached = True

        node = self.node_map[target]

        try:

            return node.ancestors()

        except RuntimeError:

            # fallback to iterative dfs

            warnings.warn(RECURSION_DEPTH_WARNING, RuntimeWarning)

            return self.iterative_dfs(node)



    def backwards_plan(self, target):

        """
@@ -154,7 +167,35 @@ class MigrationGraph(object): 
        self.ensure_not_cyclic(target, lambda x: (child.key for child in self.node_map[x].children))

        self.cached = True

        node = self.node_map[target]

        try:

            return node.descendants()

        except RuntimeError:

            # fallback to iterative dfs

            warnings.warn(RECURSION_DEPTH_WARNING, RuntimeWarning)

            return self.iterative_dfs(node, forwards=False)



    def iterative_dfs(self, start, forwards=True):

        """

        Iterative depth first search, for finding dependencies.

        """

        visited = deque()

        visited.append(start)

        if forwards:

            stack = deque(sorted(start.parents))

        else:

            stack = deque(sorted(start.children))

        while stack:

            node = stack.popleft()

            visited.appendleft(node)

            if forwards:

                children = sorted(node.parents, reverse=True)

            else:

                children = sorted(node.children, reverse=True)

            # reverse sorting is needed because prepending using deque.extendleft

            # also effectively reverses values

            stack.extendleft(children)



        return list(OrderedSet(visited))



    def root_nodes(self, app=None):

        """

tests/migrations/test_graph.py

+25 −7
Original line number Diff line number Diff line 
from unittest import expectedFailure

import warnings



from django.db.migrations.graph import (

    CircularDependencyError, MigrationGraph, NodeNotFoundError,

    RECURSION_DEPTH_WARNING, CircularDependencyError, MigrationGraph,

    NodeNotFoundError,

)

from django.test import TestCase

from django.utils.encoding import force_text
@@ -164,11 +165,14 @@ class GraphTests(TestCase): 
            graph.add_node(child, None)

            graph.add_dependency(str(i), child, parent)

            expected.append(child)

        leaf = expected[-1]



        actual = graph.node_map[root].descendants()

        self.assertEqual(expected[::-1], actual)

        forwards_plan = graph.forwards_plan(leaf)

        self.assertEqual(expected, forwards_plan)



        backwards_plan = graph.backwards_plan(root)

        self.assertEqual(expected[::-1], backwards_plan)



    @expectedFailure

    def test_graph_iterative(self):

        graph = MigrationGraph()

        root = ("app_a", "1")
@@ -180,9 +184,23 @@ class GraphTests(TestCase): 
            graph.add_node(child, None)

            graph.add_dependency(str(i), child, parent)

            expected.append(child)

        leaf = expected[-1]



        with warnings.catch_warnings(record=True) as w:

            forwards_plan = graph.forwards_plan(leaf)



        self.assertEqual(len(w), 1)

        self.assertTrue(issubclass(w[-1].category, RuntimeWarning))

        self.assertEqual(str(w[-1].message), RECURSION_DEPTH_WARNING)

        self.assertEqual(expected, forwards_plan)



        with warnings.catch_warnings(record=True) as w:

            backwards_plan = graph.backwards_plan(root)



        actual = graph.node_map[root].descendants()

        self.assertEqual(expected[::-1], actual)

        self.assertEqual(len(w), 1)

        self.assertTrue(issubclass(w[-1].category, RuntimeWarning))

        self.assertEqual(str(w[-1].message), RECURSION_DEPTH_WARNING)

        self.assertEqual(expected[::-1], backwards_plan)



    def test_plan_invalid_node(self):

        """