Reimplement DB collections for mirrors, repos and snapshots

See #765, #761

Collections were relying on keeping in-memory list of all the objects
for any kind of operation which doesn't scale well the number of
objects in the database.

With this rewrite, objects are loaded only on demand which might
be pessimization in some edge cases but should improve performance
and memory footprint signifcantly.

deb/local.go

@@ -2,6 +2,7 @@ package deb
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"log"
 	"sync"
@@ -93,8 +94,8 @@ func (repo *LocalRepo) RefKey() []byte {
 // LocalRepoCollection does listing, updating/adding/deleting of LocalRepos
 type LocalRepoCollection struct {
 	*sync.RWMutex
-	db   database.Storage
-	list []*LocalRepo
+	db    database.Storage
+	cache map[string]*LocalRepo
 }
 
 // NewLocalRepoCollection loads LocalRepos from DB and makes up collection
@@ -102,43 +103,59 @@ func NewLocalRepoCollection(db database.Storage) *LocalRepoCollection {
 	return &LocalRepoCollection{
 		RWMutex: &sync.RWMutex{},
 		db:      db,
+		cache:   make(map[string]*LocalRepo),
 	}
 }
 
-func (collection *LocalRepoCollection) loadList() {
-	if collection.list != nil {
-		return
-	}
-
-	blobs := collection.db.FetchByPrefix([]byte("L"))
-	collection.list = make([]*LocalRepo, 0, len(blobs))
-
-	for _, blob := range blobs {
-		r := &LocalRepo{}
-		if err := r.Decode(blob); err != nil {
-			log.Printf("Error decoding repo: %s\n", err)
-		} else {
-			collection.list = append(collection.list, r)
+func (collection *LocalRepoCollection) search(filter func(*LocalRepo) bool, unique bool) []*LocalRepo {
+	result := []*LocalRepo(nil)
+	for _, r := range collection.cache {
+		if filter(r) {
+			result = append(result, r)
 		}
 	}
+
+	if unique && len(result) > 0 {
+		return result
+	}
+
+	collection.db.ProcessByPrefix([]byte("L"), func(key, blob []byte) error {
+		r := &LocalRepo{}
+		if err := r.Decode(blob); err != nil {
+			log.Printf("Error decoding local repo: %s\n", err)
+			return nil
+		}
+
+		if filter(r) {
+			if _, exists := collection.cache[r.UUID]; !exists {
+				collection.cache[r.UUID] = r
+				result = append(result, r)
+				if unique {
+					return errors.New("abort")
+				}
+			}
+		}
+
+		return nil
+	})
+
+	return result
 }
 
 // Add appends new repo to collection and saves it
 func (collection *LocalRepoCollection) Add(repo *LocalRepo) error {
-	collection.loadList()
+	_, err := collection.ByName(repo.Name)
 
-	for _, r := range collection.list {
-		if r.Name == repo.Name {
-			return fmt.Errorf("local repo with name %s already exists", repo.Name)
-		}
+	if err == nil {
+		return fmt.Errorf("local repo with name %s already exists", repo.Name)
 	}
 
-	err := collection.Update(repo)
+	err = collection.Update(repo)
 	if err != nil {
 		return err
 	}
 
-	collection.list = append(collection.list, repo)
+	collection.cache[repo.UUID] = repo
 	return nil
 }
 
@@ -159,8 +176,6 @@ func (collection *LocalRepoCollection) Update(repo *LocalRepo) error {
 
 // LoadComplete loads additional information for local repo
 func (collection *LocalRepoCollection) LoadComplete(repo *LocalRepo) error {
-	collection.loadList()
-
 	encoded, err := collection.db.Get(repo.RefKey())
 	if err == database.ErrNotFound {
 		return nil
@@ -175,26 +190,39 @@ func (collection *LocalRepoCollection) LoadComplete(repo *LocalRepo) error {
 
 // ByName looks up repository by name
 func (collection *LocalRepoCollection) ByName(name string) (*LocalRepo, error) {
-	collection.loadList()
-
-	for _, r := range collection.list {
-		if r.Name == name {
-			return r, nil
-		}
+	result := collection.search(func(r *LocalRepo) bool { return r.Name == name }, true)
+	if len(result) == 0 {
+		return nil, fmt.Errorf("local repo with name %s not found", name)
 	}
-	return nil, fmt.Errorf("local repo with name %s not found", name)
+
+	return result[0], nil
 }
 
 // ByUUID looks up repository by uuid
 func (collection *LocalRepoCollection) ByUUID(uuid string) (*LocalRepo, error) {
-	collection.loadList()
-
-	for _, r := range collection.list {
-		if r.UUID == uuid {
-			return r, nil
-		}
+	if r, ok := collection.cache[uuid]; ok {
+		return r, nil
 	}
-	return nil, fmt.Errorf("local repo with uuid %s not found", uuid)
+
+	key := (&LocalRepo{UUID: uuid}).Key()
+
+	value, err := collection.db.Get(key)
+	if err == database.ErrNotFound {
+		return nil, fmt.Errorf("local repo with uuid %s not found", uuid)
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	r := &LocalRepo{}
+	err = r.Decode(value)
+
+	if err == nil {
+		collection.cache[r.UUID] = r
+	}
+
+	return r, err
 }
 
 // ForEach runs method for each repository
@@ -212,30 +240,16 @@ func (collection *LocalRepoCollection) ForEach(handler func(*LocalRepo) error) e
 
 // Len returns number of remote repos
 func (collection *LocalRepoCollection) Len() int {
-	collection.loadList()
-
-	return len(collection.list)
+	return len(collection.db.KeysByPrefix([]byte("L")))
 }
 
 // Drop removes remote repo from collection
 func (collection *LocalRepoCollection) Drop(repo *LocalRepo) error {
-	collection.loadList()
-
-	repoPosition := -1
-
-	for i, r := range collection.list {
-		if r == repo {
-			repoPosition = i
-			break
-		}
-	}
-
-	if repoPosition == -1 {
+	if _, err := collection.db.Get(repo.Key()); err == database.ErrNotFound {
 		panic("local repo not found!")
 	}
 
-	collection.list[len(collection.list)-1], collection.list[repoPosition], collection.list =
-		nil, collection.list[len(collection.list)-1], collection.list[:len(collection.list)-1]
+	delete(collection.cache, repo.UUID)
 
 	err := collection.db.Delete(repo.Key())
 	if err != nil {