server: Implement schema migrations

server/storage/schema/migration.go

@@ -0,0 +1,119 @@
+// Copyright 2021 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package schema
+
+import (
+	"fmt"
+
+	"github.com/coreos/go-semver/semver"
+	"go.etcd.io/etcd/server/v3/storage/backend"
+	"go.uber.org/zap"
+)
+
+type migrationPlan []migrationStep
+
+func newPlan(lg *zap.Logger, current semver.Version, target semver.Version) (p migrationPlan, err error) {
+	if current.Major != target.Major {
+		lg.Error("Changing major storage version is not supported",
+			zap.String("storage-version", current.String()),
+			zap.String("target-storage-version", target.String()),
+		)
+		return nil, fmt.Errorf("Changing major storage version is not supported")
+	}
+	// TODO(serathius): Implement downgrades
+	if current.Minor > target.Minor {
+		lg.Error("Target version is lower than the current version, downgrades are not yet supported",
+			zap.String("storage-version", current.String()),
+			zap.String("target-storage-version", target.String()),
+		)
+		return nil, fmt.Errorf("downgrades are not yet supported")
+	}
+	return buildPlan(current, target)
+}
+
+func buildPlan(current semver.Version, target semver.Version) (plan migrationPlan, err error) {
+	for current.Minor != target.Minor {
+		isUpgrade := current.Minor < target.Minor
+
+		changes, err := schemaChangesForVersion(current, isUpgrade)
+		if err != nil {
+			return plan, err
+		}
+		step := newMigrationStep(current, isUpgrade, changes)
+		plan = append(plan, step)
+		current = step.target
+	}
+	return plan, nil
+}
+
+func (p migrationPlan) Execute(lg *zap.Logger, tx backend.BatchTx) error {
+	tx.Lock()
+	defer tx.Unlock()
+	return p.unsafeExecute(lg, tx)
+}
+
+func (p migrationPlan) unsafeExecute(lg *zap.Logger, tx backend.BatchTx) (err error) {
+	for _, s := range p {
+		err = s.unsafeExecute(lg, tx)
+		if err != nil {
+			return err
+		}
+		lg.Info("upgraded storage version", zap.String("new-storage-version", s.target.String()))
+	}
+	return nil
+}
+
+// migrationStep represents a single migrationStep of migrating etcd storage between two minor versions.
+type migrationStep struct {
+	target  semver.Version
+	actions ActionList
+}
+
+func newMigrationStep(v semver.Version, isUpgrade bool, changes []schemaChange) (step migrationStep) {
+	step.actions = make(ActionList, len(changes))
+	for i, change := range changes {
+		if isUpgrade {
+			step.actions[i] = change.upgradeAction()
+		} else {
+			step.actions[len(changes)-1-i] = change.downgradeAction()
+		}
+	}
+	if isUpgrade {
+		step.target = semver.Version{Major: v.Major, Minor: v.Minor + 1}
+	} else {
+		step.target = semver.Version{Major: v.Major, Minor: v.Minor - 1}
+	}
+	return step
+}
+
+// execute runs actions required to migrate etcd storage between two minor versions.
+func (s migrationStep) execute(lg *zap.Logger, tx backend.BatchTx) error {
+	tx.Lock()
+	defer tx.Unlock()
+	return s.unsafeExecute(lg, tx)
+}
+
+// unsafeExecute is non thread-safe version of execute.
+func (s migrationStep) unsafeExecute(lg *zap.Logger, tx backend.BatchTx) error {
+	err := s.actions.unsafeExecute(lg, tx)
+	if err != nil {
+		return err
+	}
+	// Storage version is available since v3.6, downgrading target v3.5 should clean this field.
+	if !s.target.LessThan(V3_6) {
+		UnsafeSetStorageVersion(tx, &s.target)
+	}
+	return nil
+}