migratex api uses tx now instead of db (#939)

* migratex api uses tx now instead of db

we want to be able to do external queries outside of the migration itself
inside of the same transaction for version checking. if we don't do this, we
risk the case where we set the version to the latest but we don't run the
table creates at all, so we have a db that thinks it's up to date but doesn't
even have any tables, and on subsequent boots if a migration slides in then
the migrations will run when there are no tables. it was unlikely, but now
it's dead.

* tx friendly table exists check

the previous existence checker for dbs was relying on getting back errors
about the db not existing. if we use this in a tx, it makes the whole tx
invalid for postgres. so, now we have count the table queries which return a 1
or a 0 instead of a 1 or an error so that we can check existence inside of a
transaction. voila.

api/datastore/sql/migratex/migrate.go

@@ -12,6 +12,7 @@ import (
 	"github.com/go-sql-driver/mysql"
 	"github.com/jmoiron/sqlx"
 	"github.com/lib/pq"
+	"github.com/sirupsen/logrus"
 )
 
 var (
@@ -76,25 +77,19 @@ func (m MigFields) Version() int64                              { return m.Versi
 
 // TODO instance must have `multiStatements` set to true ?
 
-func Up(ctx context.Context, db *sqlx.DB, migs []Migration) error {
-	return migrate(ctx, db, migs, true)
+func Up(ctx context.Context, tx *sqlx.Tx, migs []Migration) error {
+	return migrate(ctx, tx, migs, true)
 }
 
-func Down(ctx context.Context, db *sqlx.DB, migs []Migration) error {
-	return migrate(ctx, db, migs, false)
+func Down(ctx context.Context, tx *sqlx.Tx, migs []Migration) error {
+	return migrate(ctx, tx, migs, false)
 }
 
-func migrate(ctx context.Context, db *sqlx.DB, migs []Migration, up bool) error {
-	var curVersion int64 // could be NilVersion, is ok
-	err := tx(ctx, db, func(tx *sqlx.Tx) error {
-		var dirty bool
-		var err error
-		curVersion, dirty, err = Version(ctx, tx)
+func migrate(ctx context.Context, tx *sqlx.Tx, migs []Migration, up bool) error {
+	curVersion, dirty, err := Version(ctx, tx)
 	if dirty {
 		return dirtyErr(curVersion)
 	}
-		return err
-	})
 	if err != nil {
 		return err
 	}
@@ -119,7 +114,7 @@ func migrate(ctx context.Context, db *sqlx.DB, migs []Migration, up bool) error
 			// XXX(reed): we could more gracefully handle concurrent databases trying to
 			// run migrations here by handling error and feeding back the version.
 			// get something working mode for now...
-			err := run(ctx, db, m, up)
+			err := run(ctx, tx, m, up)
 			if err != nil {
 				return err
 			}
@@ -129,19 +124,6 @@ func migrate(ctx context.Context, db *sqlx.DB, migs []Migration, up bool) error
 	return nil
 }
 
-func tx(ctx context.Context, db *sqlx.DB, f func(*sqlx.Tx) error) error {
-	tx, err := db.BeginTxx(ctx, nil)
-	if err != nil {
-		return err
-	}
-	err = f(tx)
-	if err != nil {
-		tx.Rollback()
-		return err
-	}
-	return tx.Commit()
-}
-
 func withLock(ctx context.Context, tx *sqlx.Tx, f func(*sqlx.Tx) error) error {
 	err := lock(ctx, tx)
 	if err != nil {
@@ -188,8 +170,7 @@ func (m MultiError) Error() string {
 	return strings.Join(strs, "\n")
 }
 
-func run(ctx context.Context, db *sqlx.DB, m Migration, up bool) error {
-	return tx(ctx, db, func(tx *sqlx.Tx) error {
+func run(ctx context.Context, tx *sqlx.Tx, m Migration, up bool) error {
 	return withLock(ctx, tx, func(tx *sqlx.Tx) error {
 		// within the transaction, we need to check the version and ensure this
 		// migration has not already been applied.
@@ -227,7 +208,6 @@ func run(ctx context.Context, db *sqlx.DB, m Migration, up bool) error {
 		err = SetVersion(ctx, tx, version, false)
 		return err
 	})
-	})
 }
 
 const advisoryLockIdSalt uint = 1486364155
@@ -297,7 +277,8 @@ func unlock(ctx context.Context, tx *sqlx.Tx) error {
 func SetVersion(ctx context.Context, tx *sqlx.Tx, version int64, dirty bool) error {
 	err := ensureVersionTable(ctx, tx)
 	if err != nil {
-		return nil
+		logrus.WithError(err).Error("error ensuring version table")
+		return err
 	}
 
 	// TODO need to handle down migration better
@@ -305,12 +286,14 @@ func SetVersion(ctx context.Context, tx *sqlx.Tx, version int64, dirty bool) err
 	// this just nukes the whole table which is kinda lame.
 	query := tx.Rebind("DELETE FROM " + MigrationsTable)
 	if _, err := tx.Exec(query); err != nil {
+		logrus.WithError(err).Error("error deleting version table")
 		return err
 	}
 
 	if version >= 0 {
 		query = tx.Rebind(`INSERT INTO ` + MigrationsTable + ` (version, dirty) VALUES (?, ?)`)
 		if _, err := tx.ExecContext(ctx, query, version, dirty); err != nil {
+			logrus.WithError(err).Error("error updating version table")
 			return err
 		}
 	}

api/datastore/sql/migratex/migrate_test.go

@@ -38,7 +38,14 @@ func TestMigrateUp(t *testing.T) {
 
 	ctx := context.Background()
 
-	err = tx(ctx, db, func(tx *sqlx.Tx) error {
+	do := func() error {
+		tx, err := db.Beginx()
+		if err != nil {
+			return err
+		}
+
+		defer tx.Commit()
+
 		version, dirty, err := Version(ctx, tx)
 		if version != NilVersion || err != nil || dirty {
 			return fmt.Errorf("version err: %v %v", err, dirty)
@@ -48,7 +55,7 @@ func TestMigrateUp(t *testing.T) {
 			return errors.New("found existing version in db, nuke it")
 		}
 
-		err = Up(ctx, db, []Migration{x})
+		err = Up(ctx, tx, []Migration{x})
 		if err != nil {
 			return err
 		}
@@ -61,7 +68,15 @@ func TestMigrateUp(t *testing.T) {
 		if version != x.Version() {
 			return errors.New("version did not update, migration should have ran.")
 		}
+		return nil
+	}
 
+	err = do()
+	if err != nil {
+		t.Fatalf("couldn't run migrations: %v", err)
+	}
+
+	do = func() error {
 		// make sure the table is there.
 		// TODO find a db agnostic way of doing this.
 		//	query := db.Rebind(`SELECT foo FROM sqlite_master WHERE type = 'table'`)
@@ -76,9 +91,10 @@ func TestMigrateUp(t *testing.T) {
 			return fmt.Errorf("migration version worked but migration didn't work: %v", result)
 		}
 		return nil
-	})
+	}
 
+	err = do()
 	if err != nil {
-		t.Fatalf("bad things happened: %v", err)
+		t.Fatalf("migration check failed: %v", err)
 	}
 }

api/datastore/sql/sql.go

@@ -151,24 +151,44 @@ func newDS(ctx context.Context, url *url.URL) (*sqlStore, error) {
 	db.SetMaxIdleConns(maxIdleConns)
 	log.WithFields(logrus.Fields{"max_idle_connections": maxIdleConns, "datastore": driver}).Info("datastore dialed")
 
-	sdb := &sqlStore{db: db}
-
-	err = sdb.runMigrations(ctx, checkExistence(db), migrations.Migrations)
-	if err != nil {
-		log.WithError(err).Error("error running migrations")
-		return nil, err
-	}
-
-	switch driver {
+	switch driver { // NOTE: fixes weird sqlite3 behavior
 	case "sqlite3":
 		db.SetMaxOpenConns(1)
 	}
+
+	sdb := &sqlStore{db: db}
+
+	// NOTE: runMigrations happens before we create all the tables, so that it
+	// can detect whether the db did not exist and insert the latest version of
+	// the migrations BEFORE the tables are created (it uses table info to
+	// determine that).
+	//
+	// we either create all the tables with the latest version of the schema,
+	// insert the latest version to the migration table and bail without running
+	// any migrations.
+	// OR
+	// run all migrations necessary to get up to the latest, inserting that version,
+	// [and the tables exist so CREATE IF NOT EXIST guards us when we run the create queries].
+	err = sdb.Tx(func(tx *sqlx.Tx) error {
+		err = sdb.runMigrations(ctx, tx, migrations.Migrations)
+		if err != nil {
+			log.WithError(err).Error("error running migrations")
+			return err
+		}
+
 		for _, v := range tables {
-		_, err = db.ExecContext(ctx, v)
+			_, err = tx.ExecContext(ctx, v)
+			if err != nil {
+				log.WithError(err).Error("error creating tables")
+				return err
+			}
+		}
+		return nil
+	})
+
 	if err != nil {
 		return nil, err
 	}
-	}
 
 	return sdb, nil
 }
@@ -208,35 +228,47 @@ func pingWithRetry(ctx context.Context, db *sqlx.DB) (err error) {
 // about the existence of the schema migration version (since migrations were
 // added to existing dbs, we need to know whether the db exists without migrations
 // or if it's brand new).
-func checkExistence(db *sqlx.DB) bool {
-	query := db.Rebind(`SELECT name FROM apps LIMIT 1`)
-	row := db.QueryRow(query)
+func checkExistence(tx *sqlx.Tx) (bool, error) {
+	query := tx.Rebind(`SELECT count(*)
+	FROM information_schema.TABLES
+	WHERE TABLE_NAME = 'apps'
+`)
 
-	var dummy string
-	err := row.Scan(&dummy)
-	if err != nil && err != sql.ErrNoRows {
-		// TODO we should probably ensure this is a certain 'no such table' error
-		// and if it's not that or err no rows, we should probably block start up.
-		// if we return false here spuriously, then migrations could be skipped,
-		// which would be bad.
-		return false
+	if tx.DriverName() == "sqlite3" {
+		// sqlite3 is special, of course
+		query = tx.Rebind(`SELECT count(*)
+		FROM sqlite_master
+		WHERE name = 'apps'
+		`)
 	}
-	return true
+
+	row := tx.QueryRow(query)
+
+	var count int
+	err := row.Scan(&count)
+	if err != nil {
+		return false, err
+	}
+
+	exists := count > 0
+	return exists, nil
 }
 
 // check if the db already existed, if the db is brand new then we can skip
 // over all the migrations BUT we must be sure to set the right migration
 // number so that only current migrations are skipped, not any future ones.
-func (ds *sqlStore) runMigrations(ctx context.Context, dbExists bool, migrations []migratex.Migration) error {
+func (ds *sqlStore) runMigrations(ctx context.Context, tx *sqlx.Tx, migrations []migratex.Migration) error {
+	dbExists, err := checkExistence(tx)
+	if err != nil {
+		return err
+	}
 	if !dbExists {
 		// set to highest and bail
-		return ds.Tx(func(tx *sqlx.Tx) error {
 		return migratex.SetVersion(ctx, tx, latestVersion(migrations), false)
-		})
 	}
 
 	// run any migrations needed to get to latest, if any
-	return migratex.Up(ctx, ds.db, migrations)
+	return migratex.Up(ctx, tx, migrations)
 }
 
 // latest version will find the latest version from a list of migration

api/datastore/sql/sql_test.go

@@ -12,6 +12,7 @@ import (
 	"github.com/fnproject/fn/api/datastore/sql/migrations"
 	logstoretest "github.com/fnproject/fn/api/logs/testing"
 	"github.com/fnproject/fn/api/models"
+	"github.com/jmoiron/sqlx"
 )
 
 // since New with fresh dbs skips all migrations:
@@ -25,7 +26,9 @@ func newWithMigrations(ctx context.Context, url *url.URL) (*sqlStore, error) {
 		return nil, err
 	}
 
-	err = migratex.Down(ctx, ds.db, migrations.Migrations)
+	err = ds.Tx(func(tx *sqlx.Tx) error {
+		return migratex.Down(ctx, tx, migrations.Migrations)
+	})
 	if err != nil {
 		return nil, err
 	}