sql: implement index catalog

sql/catalog.go

@@ -11,13 +11,15 @@ var ErrDatabaseNotFound = errors.NewKind("database not found: %s")
 type Catalog struct {
 	Databases
 	FunctionRegistry
+	*IndexRegistry
 }
 
 // NewCatalog returns a new empty Catalog.
 func NewCatalog() *Catalog {
 	return &Catalog{
 		Databases:        Databases{},
 		FunctionRegistry: NewFunctionRegistry(),
+		IndexRegistry:    NewIndexRegistry(),
 	}
 }
 

sql/index.go

@@ -1,6 +1,14 @@
 package sql
 
-import "io"
+import (
+	"context"
+	"io"
+	"reflect"
+	"strings"
+	"sync"
+
+	"gopkg.in/src-d/go-errors.v1"
+)
 
 // IndexKeyValueIter is an iterator of index key values, that is, a tuple of
 // the values that will be index keys.
@@ -28,6 +36,10 @@ type Index interface {
 	Has(key interface{}) (bool, error)
 	// ID returns the identifier of the index.
 	ID() string
+	// Database returns the database name this index belongs to.
+	Database() string
+	// Table returns the table name this index belongs to.
+	Table() string
 	// Expression returns the indexed expression.
 	Expression() Expression
 }
@@ -87,18 +99,263 @@ type Mergeable interface {
 	IsMergeable(IndexLookup) bool
 }
 
-// IndexLoader is the piece that loads indexes from disk.
-type IndexLoader interface {
-	// ID returns the unique name of the index loader.
+// IndexDriver manages the coordination between the indexes and their
+// representation in disk.
+type IndexDriver interface {
+	// ID returns the unique name of the driver.
 	ID() string
+	// Create a new index for the given expression and id.
+	Create(path, db, id string, expr Expression) (Index, error)
 	// Load the index at the given path.
 	Load(path string) (Index, error)
+	// Save the given index at the given path.
+	Save(ctx context.Context, path string, index Index, iter IndexKeyValueIter) error
+	// Delete the index with the given path.
+	Delete(path string, index Index) error
 }
 
-// IndexSaver is the piece that stores indexes in disk.
-type IndexSaver interface {
-	// ID returns the unique name of the index saver.
-	ID() string
-	// Save the given index at the given path.
-	Save(index Index, path string) error
+type indexKey struct {
+	db, id string
+}
+
+// IndexRegistry keeps track of all indexes in the engine.
+type IndexRegistry struct {
+	root string
+
+	mut      sync.RWMutex
+	indexes  map[indexKey]Index
+	statuses map[indexKey]IndexStatus
+
+	driversMut sync.RWMutex
+	drivers    map[string]IndexDriver
+
+	rcmut            sync.RWMutex
+	refCounts        map[indexKey]int
+	deleteIndexQueue map[indexKey]chan<- struct{}
+}
+
+// NewIndexRegistry returns a new Index Registry.
+func NewIndexRegistry() *IndexRegistry {
+	return &IndexRegistry{
+		indexes:          make(map[indexKey]Index),
+		statuses:         make(map[indexKey]IndexStatus),
+		drivers:          make(map[string]IndexDriver),
+		refCounts:        make(map[indexKey]int),
+		deleteIndexQueue: make(map[indexKey]chan<- struct{}),
+	}
+}
+
+// IndexDriver returns the IndexDriver with the given ID.
+func (r *IndexRegistry) IndexDriver(id string) IndexDriver {
+	r.driversMut.RLock()
+	defer r.driversMut.RUnlock()
+	return r.drivers[id]
+}
+
+// RegisterIndexDriver registers a new index driver.
+func (r *IndexRegistry) RegisterIndexDriver(driver IndexDriver) {
+	r.driversMut.Lock()
+	defer r.driversMut.Unlock()
+	r.drivers[driver.ID()] = driver
+}
+
+func (r *IndexRegistry) retainIndex(db, id string) {
+	r.rcmut.Lock()
+	defer r.rcmut.Unlock()
+	key := indexKey{db, id}
+	r.refCounts[key] = r.refCounts[key] + 1
+}
+
+// CanUseIndex returns whether the given index is ready to use or not.
+func (r *IndexRegistry) CanUseIndex(idx Index) bool {
+	r.mut.RLock()
+	defer r.mut.RUnlock()
+	return bool(r.statuses[indexKey{idx.Database(), idx.ID()}])
+}
+
+// setStatus is not thread-safe, it should be guarded using mut.
+func (r *IndexRegistry) setStatus(idx Index, status IndexStatus) {
+	r.statuses[indexKey{idx.Database(), idx.ID()}] = status
+}
+
+// ReleaseIndex releases an index after it's been used.
+func (r *IndexRegistry) ReleaseIndex(idx Index) {
+	r.rcmut.Lock()
+	defer r.rcmut.Unlock()
+	key := indexKey{idx.Database(), idx.ID()}
+	r.refCounts[key] = r.refCounts[key] - 1
+
+	if r.refCounts[key] > 0 {
+		return
+	}
+
+	if ch, ok := r.deleteIndexQueue[key]; ok {
+		close(ch)
+		delete(r.deleteIndexQueue, key)
+	}
+}
+
+// Index returns the index with the given id. It may return nil if the index is
+// not found.
+func (r *IndexRegistry) Index(db, id string) Index {
+	r.mut.RLock()
+	defer r.mut.RUnlock()
+	return r.indexes[indexKey{db, strings.ToLower(id)}]
+}
+
+// IndexByExpression returns an index by the given expression. It will return
+// nil it the index is not found.
+func (r *IndexRegistry) IndexByExpression(db string, expr Expression) Index {
+	r.mut.RLock()
+	defer r.mut.RUnlock()
+
+	for _, idx := range r.indexes {
+		if reflect.DeepEqual(idx.Expression(), expr) && idx.Database() == db {
+			r.retainIndex(db, idx.ID())
+			return idx
+		}
+	}
+	return nil
+}
+
+var (
+	// ErrIndexIDAlreadyRegistered is the error returned when there is already
+	// an index with the same ID.
+	ErrIndexIDAlreadyRegistered = errors.NewKind("an index with id %q has already been registered")
+
+	// ErrIndexExpressionAlreadyRegistered is the error returned when there is
+	// already an index with the same expression.
+	ErrIndexExpressionAlreadyRegistered = errors.NewKind("there is already an index registered for the expression %q")
+
+	// ErrIndexNotFound is returned when the index could not be found.
+	ErrIndexNotFound = errors.NewKind("index %q	was not found")
+
+	// ErrIndexDeleteInvalidStatus is returned when the index trying to delete
+	// does not have a ready state.
+	ErrIndexDeleteInvalidStatus = errors.NewKind("can't delete index %q because it's not ready for usage")
+)
+
+func (r *IndexRegistry) validateIndexToAdd(idx Index) error {
+	r.mut.RLock()
+	defer r.mut.RUnlock()
+
+	for _, i := range r.indexes {
+		if i.Database() != idx.Database() {
+			continue
+		}
+
+		if i.ID() == idx.ID() {
+			return ErrIndexIDAlreadyRegistered.New(idx.ID())
+		}
+
+		if reflect.DeepEqual(i.Expression(), idx.Expression()) {
+			return ErrIndexExpressionAlreadyRegistered.New(idx.Expression())
+		}
+	}
+
+	return nil
+}
+
+// AddIndex adds the given index to the registry. The added index will be
+// marked as creating, so nobody can't register two indexes with the same
+// expression or id while the other is still being created.
+// When something is sent through the returned channel, it means the index has
+// finished it's creation and will be marked as ready.
+func (r *IndexRegistry) AddIndex(idx Index) (chan<- struct{}, error) {
+	if err := r.validateIndexToAdd(idx); err != nil {
+		return nil, err
+	}
+
+	r.mut.Lock()
+	r.setStatus(idx, IndexNotReady)
+	r.indexes[indexKey{idx.Database(), idx.ID()}] = idx
+	r.mut.Unlock()
+
+	var created = make(chan struct{})
+	go func() {
+		<-created
+		r.mut.Lock()
+		defer r.mut.Unlock()
+		r.setStatus(idx, IndexReady)
+	}()
+
+	return created, nil
+}
+
+// DeleteIndex deletes an index from the registry by its id. First, it marks
+// the index for deletion but does not remove it, so queries that are using it
+// may still do so. The returned channel will send a message when the index can
+// be deleted from disk.
+func (r *IndexRegistry) DeleteIndex(db, id string) (<-chan struct{}, error) {
+	r.mut.RLock()
+	var key indexKey
+	for k, idx := range r.indexes {
+		if strings.ToLower(id) == idx.ID() {
+			if !r.CanUseIndex(idx) {
+				r.mut.RUnlock()
+				return nil, ErrIndexDeleteInvalidStatus.New(id)
+			}
+			r.setStatus(idx, IndexNotReady)
+			key = k
+			break
+		}
+	}
+	r.mut.RUnlock()
+
+	if key.id == "" {
+		return nil, ErrIndexNotFound.New(id)
+	}
+
+	var done = make(chan struct{}, 1)
+
+	r.rcmut.Lock()
+	// If no query is using this index just delete it right away
+	if r.refCounts[key] == 0 {
+		r.mut.Lock()
+		defer r.mut.Unlock()
+		defer r.rcmut.Unlock()
+
+		delete(r.indexes, key)
+		close(done)
+		return done, nil
+	}
+
+	var onReadyToDelete = make(chan struct{})
+	r.deleteIndexQueue[key] = onReadyToDelete
+	r.rcmut.Unlock()
+
+	go func() {
+		<-onReadyToDelete
+		r.mut.Lock()
+		defer r.mut.Unlock()
+		delete(r.indexes, key)
+
+		done <- struct{}{}
+	}()
+
+	return done, nil
+}
+
+// IndexStatus represents the current status in which the index is.
+type IndexStatus bool
+
+const (
+	// IndexNotReady means the index is not ready to be used.
+	IndexNotReady IndexStatus = false
+	// IndexReady means the index can be used.
+	IndexReady IndexStatus = true
+)
+
+// IsUsable returns whether the index can be used or not based on the status.
+func (s IndexStatus) IsUsable() bool {
+	return s == IndexReady
+}
+
+func (s IndexStatus) String() string {
+	switch s {
+	case IndexReady:
+		return "ready"
+	default:
+		return "not ready"
+	}
 }