Remove storage cache layer (#324)

The following changes have been made:
* Open *sql.DB outside of storage (and reuse the same DB for all storage
  objects)
* Test refactors (storage/mysql):
  * Moved DB-handling methods to storage_test (which contains TestMain)
  * Added a *sql.DB parameter to methods that access storage
  * Open DB connection only once for all tests
  * Cleaned DB at the beginning of every test

The changes above render the storage caching layer obsolete.

extension/builtin/default_registry.go

@@ -1,6 +1,7 @@
 package builtin
 
 import (
+	"database/sql"
 	"flag"
 
 	_ "github.com/go-sql-driver/mysql" // Load MySQL driver
@@ -15,19 +16,29 @@ var MySQLURIFlag = flag.String("mysql_uri", "test:zaphod@tcp(127.0.0.1:3306)/tes
 	"uri to use with mysql storage")
 
 // Default implementation of extension.Registry.
-type defaultRegistry struct{}
+type defaultRegistry struct {
+	db *sql.DB
+}
 
+// TODO(codingllama): Get rid of the error return
 func (r defaultRegistry) GetLogStorage(treeID int64) (storage.LogStorage, error) {
-	return mysql.NewLogStorage(treeID, *MySQLURIFlag)
+	return mysql.NewLogStorage(treeID, r.db)
 }
 
+// TODO(codingllama): Get rid of the error return
 func (r defaultRegistry) GetMapStorage(treeID int64) (storage.MapStorage, error) {
-	return mysql.NewMapStorage(treeID, *MySQLURIFlag)
+	return mysql.NewMapStorage(treeID, r.db)
 }
 
 // NewDefaultExtensionRegistry returns the default extension.Registry implementation, which is
 // backed by a MySQL database and configured via flags.
 // The returned registry is wraped in a cached registry.
 func NewDefaultExtensionRegistry() (extension.Registry, error) {
-	return extension.NewCachedRegistry(defaultRegistry{}), nil
+	db, err := mysql.OpenDB(*MySQLURIFlag)
+	if err != nil {
+		return nil, err
+	}
+	return &defaultRegistry{
+		db: db,
+	}, nil
 }

storage/mysql/log_admin.go

@@ -1,6 +1,7 @@
 package mysql
 
 import (
+	"database/sql"
 	"fmt"
 
 	"github.com/google/trillian/crypto"
@@ -29,10 +30,10 @@ const (
 
 // CreateTree instantiates a new log with default parameters.
 // TODO(codinglama): Move to admin API when the admin API is created.
-func CreateTree(treeID int64, dbURL string) error {
+func CreateTree(treeID int64, db *sql.DB) error {
 	// TODO(codinglama) replace with a GetDatabase from the new extension API when LogID is removed.
 	th := merkle.NewRFC6962TreeHasher(crypto.NewSHA256())
-	m, err := newTreeStorage(treeID, dbURL, th.Size(), defaultLogStrata, cache.PopulateLogSubtreeNodes(th))
+	m, err := newTreeStorage(treeID, db, th.Size(), defaultLogStrata, cache.PopulateLogSubtreeNodes(th))
 	if err != nil {
 		return fmt.Errorf("couldn't create a new treeStorage: %s", err)
 	}
@@ -60,10 +61,10 @@ func CreateTree(treeID int64, dbURL string) error {
 }
 
 // DeleteTree deletes a tree by the treeID.
-func DeleteTree(treeID int64, dbURL string) error {
+func DeleteTree(treeID int64, db *sql.DB) error {
 	// TODO(codinglama) replace with a GetDatabase from the new extension API when LogID is removed.
 	th := merkle.NewRFC6962TreeHasher(crypto.NewSHA256())
-	m, err := newTreeStorage(treeID, dbURL, th.Size(), defaultLogStrata, cache.PopulateLogSubtreeNodes(th))
+	m, err := newTreeStorage(treeID, db, th.Size(), defaultLogStrata, cache.PopulateLogSubtreeNodes(th))
 	if err != nil {
 		return fmt.Errorf("couldn't create a new treeStorage: %s", err)
 	}

storage/mysql/log_storage.go

@@ -75,10 +75,10 @@ type mySQLLogStorage struct {
 }
 
 // NewLogStorage creates a mySQLLogStorage instance for the specified MySQL URL.
-func NewLogStorage(id int64, dbURL string) (storage.LogStorage, error) {
+func NewLogStorage(id int64, db *sql.DB) (storage.LogStorage, error) {
 	// TODO(al): pass this through/configure from DB
 	th := merkle.NewRFC6962TreeHasher(crypto.NewSHA256())
-	ts, err := newTreeStorage(id, dbURL, th.Size(), defaultLogStrata, cache.PopulateLogSubtreeNodes(th))
+	ts, err := newTreeStorage(id, db, th.Size(), defaultLogStrata, cache.PopulateLogSubtreeNodes(th))
 	if err != nil {
 		return nil, fmt.Errorf("couldn't create a new treeStorage: %s", err)
 	}