Merge #32504

32504: sql: run check constraint mutations and validation by schema changer r=lucy-zhang a=eriktrinh

This change moves check constraint adds and drops through the schema
changer when the transaction commits, moving the constraint through the
same intermediate states as when index/columns are added or dropped. The
only small differences are:
 - Constraint adds can start in write-only and immediately start being
   enforced if all used columns are in write-only or public.
 - Constraint drops can move immediately from public to absent if they
   have not yet been validated.

Therefore, the check constraint is no longer immediately public when it
is added, but allows data validation of the constraint to be performed
when the constraint is added (and is now the default behaviour).
Constraints can now also be added on columns in the process of being
added.

This change also ensures that there are no data anomalies in either
versions of the schema when dropping a validated check constraint, as
previously the transition moved the constraint from public -> absent.
Writes on the new version were not being checked even though nodes on an
older version expect all rows to conform to the constraint.

Release note (sql change): Check constraint adds by default will
validate table data with the added constraint asynchronously after the
transaction commits.

Co-authored-by: Erik Trinh <erik@cockroachlabs.com>

pkg/sql/alter_table.go

@@ -15,7 +15,6 @@
 package sql
 
 import (
-	"bytes"
 	"context"
 	gojson "encoding/json"
 	"fmt"
@@ -180,6 +179,11 @@ func (n *alterTableNode) startExec(params runParams) error {
 			for k := range info {
 				inuseNames[k] = struct{}{}
 			}
+			for _, m := range n.tableDesc.Mutations {
+				if ck := m.GetCheck(); ck != nil {
+					inuseNames[ck.Name] = struct{}{}
+				}
+			}
 			switch d := t.ConstraintDef.(type) {
 			case *tree.UniqueConstraintTableDef:
 				if d.PrimaryKey {
@@ -213,14 +217,17 @@ func (n *alterTableNode) startExec(params runParams) error {
 				}
 
 			case *tree.CheckConstraintTableDef:
+				// A previous command could have added a column which the new constraint uses,
+				// allocate IDs now.
+				if err != n.tableDesc.AllocateIDs() {
+					return err
+				}
 				ck, err := MakeCheckConstraint(params.ctx,
 					n.tableDesc, d, inuseNames, &params.p.semaCtx, params.EvalContext(), n.n.Table)
 				if err != nil {
 					return err
 				}
-				ck.Validity = sqlbase.ConstraintValidity_Unvalidated
-				n.tableDesc.Checks = append(n.tableDesc.Checks, ck)
-				descriptorChanged = true
+				n.tableDesc.AddCheckMutation(*ck, sqlbase.DescriptorMutation_ADD)
 
 			case *tree.ForeignKeyConstraintTableDef:
 				for _, colName := range d.FromCols {
@@ -404,6 +411,8 @@ func (n *alterTableNode) startExec(params runParams) error {
 					return err
 				} else if !used {
 					validChecks = append(validChecks, check)
+				} else {
+					n.tableDesc.MaybeAddCheckDropMutation(*check)
 				}
 			}
 
@@ -419,6 +428,17 @@ func (n *alterTableNode) startExec(params runParams) error {
 				return err
 			}
 
+			// Check that no dependent check constraints are queued to be added.
+			for _, m := range n.tableDesc.Mutations {
+				if ck := m.GetCheck(); ck != nil && m.Direction == sqlbase.DescriptorMutation_ADD {
+					if used, err := ck.UsesColumn(n.tableDesc.TableDesc(), col.ID); err != nil {
+						return err
+					} else if used {
+						return fmt.Errorf("referencing constraint %q in the middle of being added, try again later", ck.Name)
+					}
+				}
+			}
+
 			found := false
 			for i := range n.tableDesc.Columns {
 				if n.tableDesc.Columns[i].ID == col.ID {
@@ -451,13 +471,19 @@ func (n *alterTableNode) startExec(params runParams) error {
 			case sqlbase.ConstraintTypeUnique:
 				return fmt.Errorf("UNIQUE constraint depends on index %q, use DROP INDEX with CASCADE if you really want to drop it", t.Constraint)
 			case sqlbase.ConstraintTypeCheck:
-				for i := range n.tableDesc.Checks {
-					if n.tableDesc.Checks[i].Name == name {
+				found := false
+				for i, ck := range n.tableDesc.Checks {
+					if ck.Name == name {
+						n.tableDesc.MaybeAddCheckDropMutation(*ck)
 						n.tableDesc.Checks = append(n.tableDesc.Checks[:i], n.tableDesc.Checks[i+1:]...)
 						descriptorChanged = true
+						found = true
 						break
 					}
 				}
+				if !found {
+					return fmt.Errorf("constraint %q in the middle of being added, try again later", t.Constraint)
+				}
 			case sqlbase.ConstraintTypeFK:
 				idx, err := n.tableDesc.FindIndexByID(details.Index.ID)
 				if err != nil {
@@ -496,7 +522,7 @@ func (n *alterTableNode) startExec(params runParams) error {
 					}
 				}
 				if !found {
-					panic("constraint returned by GetConstraintInfo not found")
+					return fmt.Errorf("constraint %q in the middle of being added, try again later", t.Constraint)
 				}
 				ck := n.tableDesc.Checks[idx]
 				if err := params.p.validateCheckExpr(
@@ -772,19 +798,6 @@ func applyColumnMutation(
 	return nil
 }
 
-func labeledRowValues(cols []sqlbase.ColumnDescriptor, values tree.Datums) string {
-	var s bytes.Buffer
-	for i := range cols {
-		if i != 0 {
-			s.WriteString(`, `)
-		}
-		s.WriteString(cols[i].Name)
-		s.WriteString(`=`)
-		s.WriteString(values[i].String())
-	}
-	return s.String()
-}
-
 // injectTableStats implements the INJECT STATISTICS command, which deletes any
 // existing statistics on the table and replaces them with the statistics in the
 // given json object (in the same format as the result of SHOW STATISTICS USING

pkg/sql/backfill.go

@@ -41,9 +41,15 @@ const (
 	// processed per chunk during column truncate or backfill.
 	columnTruncateAndBackfillChunkSize = 200
 
+	// checkConstraintBackfillChunkSize is the maximum number of rows
+	// processed per chunk during check constraint validation. This value
+	// is larger than the other chunk constants because the operation involves
+	// only running a scan and does not write.
+	checkConstraintBackfillChunkSize = 1600
+
 	// indexTruncateChunkSize is the maximum number of index entries truncated
-	// per chunk during an index truncation. This value is larger than the
-	// other chunk constants because the operation involves only running a
+	// per chunk during an index truncation. This value is larger than other
+	// chunk constants because the operation involves only running a
 	// DeleteRange().
 	indexTruncateChunkSize = 600
 
@@ -132,13 +138,18 @@ func (sc *SchemaChanger) runBackfill(
 		tableDesc.Name, tableDesc.Version, sc.mutationID)
 
 	needColumnBackfill := false
+	needCheckValidation := false
 	for _, m := range tableDesc.Mutations {
 		if m.MutationID != sc.mutationID {
 			break
 		}
 		switch m.Direction {
 		case sqlbase.DescriptorMutation_ADD:
 			switch t := m.Descriptor_.(type) {
+			case *sqlbase.DescriptorMutation_Check:
+				if t.Check.Validity == sqlbase.ConstraintValidity_Validating {
+					needCheckValidation = true
+				}
 			case *sqlbase.DescriptorMutation_Column:
 				if sqlbase.ColumnNeedsBackfill(m.GetColumn()) {
 					needColumnBackfill = true
@@ -151,6 +162,8 @@ func (sc *SchemaChanger) runBackfill(
 
 		case sqlbase.DescriptorMutation_DROP:
 			switch t := m.Descriptor_.(type) {
+			case *sqlbase.DescriptorMutation_Check:
+				// Nothing to do.
 			case *sqlbase.DescriptorMutation_Column:
 				needColumnBackfill = true
 			case *sqlbase.DescriptorMutation_Index:
@@ -186,6 +199,13 @@ func (sc *SchemaChanger) runBackfill(
 		}
 	}
 
+	// Validate checks.
+	if needCheckValidation {
+		if err := sc.validateChecks(ctx, evalCtx, lease, version); err != nil {
+			return err
+		}
+	}
+
 	return nil
 }
 
@@ -202,6 +222,18 @@ func (sc *SchemaChanger) getTableVersion(
 	return tableDesc, nil
 }
 
+func (sc *SchemaChanger) validateChecks(
+	ctx context.Context,
+	evalCtx *extendedEvalContext,
+	lease *sqlbase.TableDescriptor_SchemaChangeLease,
+	version sqlbase.DescriptorVersion,
+) error {
+	return sc.distBackfill(
+		ctx, evalCtx,
+		lease, version, checkConstraintBackfill, checkConstraintBackfillChunkSize,
+		backfill.CheckMutationFilter)
+}
+
 func (sc *SchemaChanger) truncateIndexes(
 	ctx context.Context,
 	lease *sqlbase.TableDescriptor_SchemaChangeLease,
@@ -286,6 +318,7 @@ const (
 	_ backfillType = iota
 	columnBackfill
 	indexBackfill
+	checkConstraintBackfill
 )
 
 // getJobIDForMutationWithDescriptor returns a job id associated with a mutation given
@@ -517,9 +550,9 @@ func runSchemaChangesInTxn(
 		return nil
 	}
 
-	// Only needed because columnBackfillInTxn() backfills
-	// all column mutations.
-	doneColumnBackfill := false
+	// Only needed because columnBackfillInTxn() and checkValidateInTxn()
+	// backfills are applied to all related mutations.
+	doneColumnBackfill, doneCheckValidation := false, false
 	for _, m := range tableDesc.Mutations {
 		immutDesc := sqlbase.NewImmutableTableDescriptor(*tableDesc.TableDesc())
 		switch m.Direction {
@@ -539,6 +572,15 @@ func runSchemaChangesInTxn(
 					return err
 				}
 
+			case *sqlbase.DescriptorMutation_Check:
+				if doneCheckValidation || m.GetCheck().Validity != sqlbase.ConstraintValidity_Validating {
+					break
+				}
+				if err := checkValidateInTxn(ctx, txn, evalCtx, immutDesc, traceKV); err != nil {
+					return err
+				}
+				doneCheckValidation = true
+
 			default:
 				return errors.Errorf("unsupported mutation: %+v", m)
 			}
@@ -560,6 +602,9 @@ func runSchemaChangesInTxn(
 					return err
 				}
 
+			case *sqlbase.DescriptorMutation_Check:
+				// No-op.
+
 			default:
 				return errors.Errorf("unsupported mutation: %+v", m)
 			}
@@ -574,6 +619,29 @@ func runSchemaChangesInTxn(
 	return nil
 }
 
+func checkValidateInTxn(
+	ctx context.Context,
+	txn *client.Txn,
+	evalCtx *tree.EvalContext,
+	tableDesc *sqlbase.ImmutableTableDescriptor,
+	traceKV bool,
+) error {
+	var backfiller backfill.CheckBackfiller
+	if err := backfiller.Init(evalCtx, tableDesc); err != nil {
+		return err
+	}
+
+	sp := tableDesc.PrimaryIndexSpan()
+	for sp.Key != nil {
+		var err error
+		sp.Key, err = backfiller.RunCheckBackfillChunk(ctx, txn, tableDesc, sp, checkConstraintBackfillChunkSize, traceKV)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // columnBackfillInTxn backfills columns for all mutation columns in
 // the mutation list.
 func columnBackfillInTxn(