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Fix cycle detection for foreign keys (#15458)
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Signed-off-by: Manan Gupta <manan@planetscale.com>
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@GuptaManan100
GuptaManan100 authored Mar 13, 2024
1 parent f889134 commit d119295
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Showing 6 changed files with 223 additions and 35 deletions.
10 changes: 5 additions & 5 deletions go/vt/graph/graph.go
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Original file line number Diff line number Diff line change
Expand Up @@ -83,10 +83,10 @@ func (gr *Graph[C]) Empty() bool {
// HasCycles checks whether the given graph has a cycle or not.
// We are using a well-known DFS based colouring algorithm to check for cycles.
// Look at https://cp-algorithms.com/graph/finding-cycle.html for more details on the algorithm.
func (gr *Graph[C]) HasCycles() bool {
func (gr *Graph[C]) HasCycles() (bool, []C) {
// If the graph is empty, then we don't need to check anything.
if gr.Empty() {
return false
return false, nil
}
// Initialize the coloring map.
// 0 represents white.
Expand All @@ -96,12 +96,12 @@ func (gr *Graph[C]) HasCycles() bool {
for vertex := range gr.edges {
// If any vertex is still white, we initiate a new DFS.
if color[vertex] == white {
if hasCycle, _ := gr.hasCyclesDfs(color, vertex); hasCycle {
return true
if hasCycle, cycle := gr.hasCyclesDfs(color, vertex); hasCycle {
return true, cycle
}
}
}
return false
return false, nil
}

// GetCycles returns all known cycles in the graph.
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6 changes: 4 additions & 2 deletions go/vt/graph/graph_test.go
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Expand Up @@ -82,7 +82,8 @@ func TestIntegerGraph(t *testing.T) {
}
require.Equal(t, tt.wantedGraph, graph.PrintGraph())
require.Equal(t, tt.wantEmpty, graph.Empty())
require.Equal(t, tt.wantHasCycles, graph.HasCycles())
hasCycle, _ := graph.HasCycles()
require.Equal(t, tt.wantHasCycles, hasCycle)
})
}
}
Expand Down Expand Up @@ -155,7 +156,8 @@ F - A`,
}
require.Equal(t, tt.wantedGraph, graph.PrintGraph())
require.Equal(t, tt.wantEmpty, graph.Empty())
require.Equal(t, tt.wantHasCycles, graph.HasCycles())
hasCycle, _ := graph.HasCycles()
require.Equal(t, tt.wantHasCycles, hasCycle)
if tt.wantCycles == nil {
tt.wantCycles = map[string][]string{}
}
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10 changes: 10 additions & 0 deletions go/vt/sqlparser/ast_funcs.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2556,6 +2556,16 @@ func (ra ReferenceAction) IsRestrict() bool {
}
}

// IsCascade returns true if the reference action is of cascade type.
func (ra ReferenceAction) IsCascade() bool {
switch ra {
case Cascade:
return true
default:
return false
}
}

// IsLiteral returns true if the expression is of a literal type.
func IsLiteral(expr Expr) bool {
switch expr.(type) {
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2 changes: 1 addition & 1 deletion go/vt/vterrors/code.go
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Original file line number Diff line number Diff line change
Expand Up @@ -89,7 +89,7 @@ var (
VT09016 = errorWithState("VT09016", vtrpcpb.Code_FAILED_PRECONDITION, RowIsReferenced2, "Cannot delete or update a parent row: a foreign key constraint fails", "SET DEFAULT is not supported by InnoDB")
VT09017 = errorWithoutState("VT09017", vtrpcpb.Code_FAILED_PRECONDITION, "%s", "Invalid syntax for the statement type.")
VT09018 = errorWithoutState("VT09018", vtrpcpb.Code_FAILED_PRECONDITION, "%s", "Invalid syntax for the vindex function statement.")
VT09019 = errorWithoutState("VT09019", vtrpcpb.Code_FAILED_PRECONDITION, "keyspace '%s' has cyclic foreign keys", "Vitess doesn't support cyclic foreign keys.")
VT09019 = errorWithoutState("VT09019", vtrpcpb.Code_FAILED_PRECONDITION, "keyspace '%s' has cyclic foreign keys. Cycle exists between %v", "Vitess doesn't support cyclic foreign keys.")
VT09020 = errorWithoutState("VT09020", vtrpcpb.Code_FAILED_PRECONDITION, "can not use multiple vindex hints for table %s", "Vitess does not allow using multiple vindex hints on the same table.")
VT09021 = errorWithState("VT09021", vtrpcpb.Code_FAILED_PRECONDITION, KeyDoesNotExist, "Vindex '%s' does not exist in table '%s'", "Vindex hints have to reference an existing vindex, and no such vindex could be found for the given table.")

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61 changes: 39 additions & 22 deletions go/vt/vtgate/vschema_manager.go
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Original file line number Diff line number Diff line change
Expand Up @@ -260,43 +260,60 @@ func (vm *VSchemaManager) updateFromSchema(vschema *vindexes.VSchema) {
}
}

type tableCol struct {
tableName sqlparser.TableName
colNames sqlparser.Columns
}

var tableColHash = func(tc tableCol) string {
res := sqlparser.String(tc.tableName)
for _, colName := range tc.colNames {
res += "|" + sqlparser.String(colName)
}
return res
}

func markErrorIfCyclesInFk(vschema *vindexes.VSchema) {
for ksName, ks := range vschema.Keyspaces {
// Only check cyclic foreign keys for keyspaces that have
// foreign keys managed in Vitess.
if ks.ForeignKeyMode != vschemapb.Keyspace_managed {
continue
}
/*
3 cases for creating the graph for cycle detection:
1. ON DELETE RESTRICT ON UPDATE RESTRICT: This is the simplest case where no update/delete is required on the child table, we only need to verify whether a value exists or not. So we don't need to add any edge for this case.
2. ON DELETE SET NULL, ON UPDATE SET NULL, ON UPDATE CASCADE: In this case having any update/delete on any of the columns in the parent side of the foreign key will make a corresponding delete/update on all the column in the child side of the foreign key. So we will add an edge from all the columns in the parent side to all the columns in the child side.
3. ON DELETE CASCADE: This is a special case wherein a deletion on the parent table will affect all the columns in the child table irrespective of the columns involved in the foreign key! So, we'll add an edge from all the columns in the parent side of the foreign key to all the columns of the child table.
*/
g := graph.NewGraph[string]()
for _, table := range ks.Tables {
for _, cfk := range table.ChildForeignKeys {
// Check for case 1.
if cfk.OnUpdate.IsRestrict() && cfk.OnDelete.IsRestrict() {
continue
}

childTable := cfk.Table
parentVertex := tableCol{
tableName: table.GetTableName(),
colNames: cfk.ParentColumns,
var parentVertices []string
var childVertices []string
for _, column := range cfk.ParentColumns {
parentVertices = append(parentVertices, sqlparser.String(sqlparser.NewColNameWithQualifier(column.String(), table.GetTableName())))
}
childVertex := tableCol{
tableName: childTable.GetTableName(),
colNames: cfk.ChildColumns,

// Check for case 3.
if cfk.OnDelete.IsCascade() {
for _, column := range childTable.Columns {
childVertices = append(childVertices, sqlparser.String(sqlparser.NewColNameWithQualifier(column.Name.String(), childTable.GetTableName())))
}
} else {
// Case 2.
for _, column := range cfk.ChildColumns {
childVertices = append(childVertices, sqlparser.String(sqlparser.NewColNameWithQualifier(column.String(), childTable.GetTableName())))
}
}
g.AddEdge(tableColHash(parentVertex), tableColHash(childVertex))
addCrossEdges(g, parentVertices, childVertices)
}
}
if g.HasCycles() {
ks.Error = vterrors.VT09019(ksName)
hasCycle, cycle := g.HasCycles()
if hasCycle {
ks.Error = vterrors.VT09019(ksName, cycle)
}
}
}

// addCrossEdges adds the edges from all the vertices in the first list to all the vertices in the second list.
func addCrossEdges(g *graph.Graph[string], from []string, to []string) {
for _, fromStr := range from {
for _, toStr := range to {
g.AddEdge(fromStr, toStr)
}
}
}
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169 changes: 164 additions & 5 deletions go/vt/vtgate/vschema_manager_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -449,7 +449,7 @@ func TestMarkErrorIfCyclesInFk(t *testing.T) {
errWanted string
}{
{
name: "Has a cycle",
name: "Has a direct cycle",
getVschema: func() *vindexes.VSchema {
vschema := &vindexes.VSchema{
Keyspaces: map[string]*vindexes.KeyspaceSchema{
Expand All @@ -472,13 +472,44 @@ func TestMarkErrorIfCyclesInFk(t *testing.T) {
},
},
}
_ = vschema.AddForeignKey("ks", "t2", createFkDefinition([]string{"col"}, "t1", []string{"col"}, sqlparser.Cascade, sqlparser.Cascade))
_ = vschema.AddForeignKey("ks", "t3", createFkDefinition([]string{"col"}, "t2", []string{"col"}, sqlparser.Cascade, sqlparser.Cascade))
_ = vschema.AddForeignKey("ks", "t1", createFkDefinition([]string{"col"}, "t3", []string{"col"}, sqlparser.Cascade, sqlparser.Cascade))
_ = vschema.AddForeignKey("ks", "t2", createFkDefinition([]string{"col"}, "t1", []string{"col"}, sqlparser.SetNull, sqlparser.SetNull))
_ = vschema.AddForeignKey("ks", "t3", createFkDefinition([]string{"col"}, "t2", []string{"col"}, sqlparser.SetNull, sqlparser.SetNull))
_ = vschema.AddForeignKey("ks", "t1", createFkDefinition([]string{"col"}, "t3", []string{"col"}, sqlparser.SetNull, sqlparser.SetNull))
return vschema
},
errWanted: "VT09019: keyspace 'ks' has cyclic foreign keys",
},
{
name: "Has a direct cycle but there is a restrict constraint in between",
getVschema: func() *vindexes.VSchema {
vschema := &vindexes.VSchema{
Keyspaces: map[string]*vindexes.KeyspaceSchema{
ksName: {
ForeignKeyMode: vschemapb.Keyspace_managed,
Tables: map[string]*vindexes.Table{
"t1": {
Name: sqlparser.NewIdentifierCS("t1"),
Keyspace: keyspace,
},
"t2": {
Name: sqlparser.NewIdentifierCS("t2"),
Keyspace: keyspace,
},
"t3": {
Name: sqlparser.NewIdentifierCS("t3"),
Keyspace: keyspace,
},
},
},
},
}
_ = vschema.AddForeignKey("ks", "t2", createFkDefinition([]string{"col"}, "t1", []string{"col"}, sqlparser.SetNull, sqlparser.SetNull))
_ = vschema.AddForeignKey("ks", "t3", createFkDefinition([]string{"col"}, "t2", []string{"col"}, sqlparser.Restrict, sqlparser.Restrict))
_ = vschema.AddForeignKey("ks", "t1", createFkDefinition([]string{"col"}, "t3", []string{"col"}, sqlparser.SetNull, sqlparser.SetNull))
return vschema
},
errWanted: "",
},
{
name: "No cycle",
getVschema: func() *vindexes.VSchema {
Expand Down Expand Up @@ -508,14 +539,142 @@ func TestMarkErrorIfCyclesInFk(t *testing.T) {
return vschema
},
errWanted: "",
}, {
name: "Self-referencing foreign key with delete cascade",
getVschema: func() *vindexes.VSchema {
vschema := &vindexes.VSchema{
Keyspaces: map[string]*vindexes.KeyspaceSchema{
ksName: {
ForeignKeyMode: vschemapb.Keyspace_managed,
Tables: map[string]*vindexes.Table{
"t1": {
Name: sqlparser.NewIdentifierCS("t1"),
Keyspace: keyspace,
Columns: []vindexes.Column{
{
Name: sqlparser.NewIdentifierCI("id"),
},
{
Name: sqlparser.NewIdentifierCI("manager_id"),
},
},
},
},
},
},
}
_ = vschema.AddForeignKey("ks", "t1", createFkDefinition([]string{"manager_id"}, "t1", []string{"id"}, sqlparser.SetNull, sqlparser.Cascade))
return vschema
},
errWanted: "VT09019: keyspace 'ks' has cyclic foreign keys. Cycle exists between [ks.t1.id ks.t1.id]",
}, {
name: "Self-referencing foreign key without delete cascade",
getVschema: func() *vindexes.VSchema {
vschema := &vindexes.VSchema{
Keyspaces: map[string]*vindexes.KeyspaceSchema{
ksName: {
ForeignKeyMode: vschemapb.Keyspace_managed,
Tables: map[string]*vindexes.Table{
"t1": {
Name: sqlparser.NewIdentifierCS("t1"),
Keyspace: keyspace,
Columns: []vindexes.Column{
{
Name: sqlparser.NewIdentifierCI("id"),
},
{
Name: sqlparser.NewIdentifierCI("manager_id"),
},
},
},
},
},
},
}
_ = vschema.AddForeignKey("ks", "t1", createFkDefinition([]string{"manager_id"}, "t1", []string{"id"}, sqlparser.SetNull, sqlparser.SetNull))
return vschema
},
errWanted: "",
}, {
name: "Has an indirect cycle because of cascades",
getVschema: func() *vindexes.VSchema {
vschema := &vindexes.VSchema{
Keyspaces: map[string]*vindexes.KeyspaceSchema{
ksName: {
ForeignKeyMode: vschemapb.Keyspace_managed,
Tables: map[string]*vindexes.Table{
"t1": {
Name: sqlparser.NewIdentifierCS("t1"),
Keyspace: keyspace,
Columns: []vindexes.Column{
{
Name: sqlparser.NewIdentifierCI("a"),
},
{
Name: sqlparser.NewIdentifierCI("b"),
},
{
Name: sqlparser.NewIdentifierCI("c"),
},
},
},
"t2": {
Name: sqlparser.NewIdentifierCS("t2"),
Keyspace: keyspace,
Columns: []vindexes.Column{
{
Name: sqlparser.NewIdentifierCI("d"),
},
{
Name: sqlparser.NewIdentifierCI("e"),
},
{
Name: sqlparser.NewIdentifierCI("f"),
},
},
},
},
},
},
}
_ = vschema.AddForeignKey("ks", "t2", createFkDefinition([]string{"f"}, "t1", []string{"a"}, sqlparser.SetNull, sqlparser.Cascade))
_ = vschema.AddForeignKey("ks", "t1", createFkDefinition([]string{"b"}, "t2", []string{"e"}, sqlparser.SetNull, sqlparser.Cascade))
return vschema
},
errWanted: "VT09019: keyspace 'ks' has cyclic foreign keys",
}, {
name: "Cycle part of a multi-column foreign key",
getVschema: func() *vindexes.VSchema {
vschema := &vindexes.VSchema{
Keyspaces: map[string]*vindexes.KeyspaceSchema{
ksName: {
ForeignKeyMode: vschemapb.Keyspace_managed,
Tables: map[string]*vindexes.Table{
"t1": {
Name: sqlparser.NewIdentifierCS("t1"),
Keyspace: keyspace,
},
"t2": {
Name: sqlparser.NewIdentifierCS("t2"),
Keyspace: keyspace,
},
},
},
},
}
_ = vschema.AddForeignKey("ks", "t2", createFkDefinition([]string{"e", "f"}, "t1", []string{"a", "b"}, sqlparser.SetNull, sqlparser.SetNull))
_ = vschema.AddForeignKey("ks", "t1", createFkDefinition([]string{"b"}, "t2", []string{"e"}, sqlparser.SetNull, sqlparser.SetNull))
return vschema
},
errWanted: "VT09019: keyspace 'ks' has cyclic foreign keys",
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
vschema := tt.getVschema()
markErrorIfCyclesInFk(vschema)
if tt.errWanted != "" {
require.EqualError(t, vschema.Keyspaces[ksName].Error, tt.errWanted)
require.ErrorContains(t, vschema.Keyspaces[ksName].Error, tt.errWanted)
return
}
require.NoError(t, vschema.Keyspaces[ksName].Error)
Expand Down

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