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Add documentation for metadata database

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Add documentation and explanation for migrations.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>
This commit is contained in:
Derek McGowan 2017-10-05 17:03:38 -07:00
parent 8558b98eb1
commit e4defbcb6d
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2 changed files with 32 additions and 0 deletions
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22
metadata/db.go
View File

@ -27,12 +27,19 @@ const (
dbVersion = 1
)
// DB represents a metadata database backed by a bolt
// database. The database is fully namespaced and stores
// image, container, namespace, snapshot, and content data
// while proxying data shared across namespaces to backend
// datastores for content and snapshots.
type DB struct {
db *bolt.DB
ss map[string]snapshot.Snapshotter
cs content.Store
}
// NewDB creates a new metadata database using the provided
// bolt database, content store, and snapshotters.
func NewDB(db *bolt.DB, cs content.Store, ss map[string]snapshot.Snapshotter) *DB {
return &DB{
db: db,
@ -41,6 +48,8 @@ func NewDB(db *bolt.DB, cs content.Store, ss map[string]snapshot.Snapshotter) *D
}
}
// Init ensures the database is at the correct version
// and performs any needed migrations.
func (m *DB) Init(ctx context.Context) error {
// errSkip is used when no migration or version needs to be written
// to the database and the transaction can be immediately rolled
@ -54,7 +63,14 @@ func (m *DB) Init(ctx context.Context) error {
version = 0
)
// i represents the index of the first migration
// which must be run to get the database up to date.
// The migration's version will be checked in reverse
// order, decrementing i for each migration which
// represents a version newer than the current
// database version
i := len(migrations)
for ; i > 0; i-- {
migration := migrations[i-1]
@ -116,6 +132,8 @@ func (m *DB) Init(ctx context.Context) error {
return err
}
// ContentStore returns a namespaced content store
// proxied to a content store.
func (m *DB) ContentStore() content.Store {
if m.cs == nil {
return nil
@ -123,6 +141,8 @@ func (m *DB) ContentStore() content.Store {
return newContentStore(m, m.cs)
}
// Snapshotter returns a namespaced content store for
// the requested snapshotter name proxied to a snapshotter.
func (m *DB) Snapshotter(name string) snapshot.Snapshotter {
sn, ok := m.ss[name]
if !ok {
@ -131,10 +151,12 @@ func (m *DB) Snapshotter(name string) snapshot.Snapshotter {
return newSnapshotter(m, name, sn)
}
// View runs a readonly transaction on the metadata store.
func (m *DB) View(fn func(*bolt.Tx) error) error {
return m.db.View(fn)
}
// Update runs a writable transation on the metadata store.
func (m *DB) Update(fn func(*bolt.Tx) error) error {
return m.db.Update(fn)
}

10
metadata/migrations.go
View File

@ -8,6 +8,16 @@ type migration struct {
migrate func(*bolt.Tx) error
}
// migrations stores the list of database migrations
// for each update to the database schema. The migrations
// array MUST be ordered by version from least to greatest.
// The last entry in the array should correspond to the
// schemaVersion and dbVersion constants.
// A migration test MUST be added for each migration in
// the array.
// The migrate function can safely assume the version
// of the data it is migrating from is the previous version
// of the database.
var migrations = []migration{
{
schema: "v1",