diff --git a/schema.go b/schema.go
index 836a836..c7b5894 100644
--- a/schema.go
+++ b/schema.go
@@ -1,3 +1,22 @@
+/*
+Package dbschema is used to keep the SQL schema up to date.
+
+	func sqlProvider(dbName string, version int) (sql []byte, found bool) {
+		// read an SQL file and return the contents
+		return
+	}
+
+	upgrader := dbschema.NewUpgrader()
+	upgrader.SetSqlCallback(sqlProvider)
+
+	if err = upgrader.AddDatabase("127.0.0.1", 5432, "foo", "postgres", "password"); err != nil {
+		panic(err)
+	}
+
+	if err = upgrader.Run(); err != nil {
+		panic(err)
+	}
+*/
 package dbschema
 
 import (
@@ -8,6 +27,7 @@ import (
 	"database/sql"
 )
 
+// An upgrader verifies the schema for one or more databases and upgrades them if possible.
 type Upgrader struct {
 	databases map[string]Database
 	logCallback func(string, string)
diff --git a/upgrader.go b/upgrader.go
index 13e7c38..820aa3f 100644
--- a/upgrader.go
+++ b/upgrader.go
@@ -1,6 +1,9 @@
 package dbschema
 
 import (
+	// External
+	"github.com/lib/pq"
+
 	// Standard
 	"database/sql"
 	"fmt"
@@ -9,19 +12,49 @@ import (
 func defaultCallback(topic, msg string) {// {{{
 	fmt.Printf("[%s] %s\n", topic, msg)
 }// }}}
-func NewUpgrader(host string, port int, dbName, user, pass string) (upgrader Upgrader, err error) {// {{{
+
+// NewUpgrader creates an upgrader with an empty list of databases.
+func NewUpgrader() (upgrader Upgrader) {// {{{
 	upgrader.logCallback = defaultCallback
 	upgrader.databases = map[string]Database{}
 	return
 }// }}}
 
+// SetLogCallback allows to set a callback for custom logging.
 func (upgrader *Upgrader) SetLogCallback(callback func(string, string)) {// {{{
 	upgrader.logCallback = callback
 }// }}}
+// SetSqlCallback is required for providing the SQL schema updates.
 func (upgrader *Upgrader) SetSqlCallback(callback func(string, int) ([]byte, bool)) {// {{{
 	upgrader.sqlCallback = callback
 }// }}}
 
+func (dbase Database) createSchemaTable() (err error) {// {{{
+	dbase.upgrader.logCallback("create", fmt.Sprintf("%s, _db.schema", dbase.DbName))
+	_, err = dbase.db.Exec(`CREATE SCHEMA "_db"`)
+
+	// Error code 42P06 "duplicate_schema" is an OK error,
+	// table can still be missing and created.
+	pqErr, _ := err.(*pq.Error)
+	if pqErr != nil && pqErr.Code != "42P06" {
+		return
+	}
+
+	_, err = dbase.db.Exec(`
+		CREATE TABLE "_db"."schema" (
+			version  int4      NOT NULL,
+			updated  timestamp NOT NULL DEFAULT NOW(),
+
+			CONSTRAINT schema_pk PRIMARY KEY (version)
+		)`,
+	)
+	return
+}// }}}
+func (dbase Database) appendSchemaVersion(version int) (err error) {// {{{
+	_, err = dbase.db.Exec(`INSERT INTO _db.schema(version) VALUES($1)`, version)
+	return
+}// }}}
+
 func (dbase Database) verifySchemaTable() (err error) {// {{{
 	var rows *sql.Rows
 	if rows, err = dbase.db.Query(
@@ -41,37 +74,21 @@ func (dbase Database) verifySchemaTable() (err error) {// {{{
 		return
 	}
 
-	if !exists {
-		dbase.upgrader.logCallback("create", fmt.Sprintf("%s, _db.schema", dbase.DbName))
-		dbase.db.Exec(`CREATE SCHEMA "_db"`)
-
-		if _, err = dbase.db.Exec(`
-			CREATE TABLE "_db"."schema" (
-				version  int4      NOT NULL,
-				updated  timestamp NOT NULL DEFAULT NOW(),
-
-				CONSTRAINT schema_pk PRIMARY KEY (version)
-			)`,
-		); err != nil {
-			return
-		}
+	if exists {
+		return
 	}
+	err = dbase.createSchemaTable()
 	return
 }// }}}
 func (dbase Database) verifySchemaEntry() (err error) {// {{{
-	var rows *sql.Rows
-	rows, err = dbase.db.Query(`SELECT version FROM _db.schema LIMIT 1`)
-	if err != nil {
-		return
-	}
-	defer rows.Close()
+	var version int
+	var row *sql.Row
+	row = dbase.db.QueryRow(`SELECT version FROM _db.schema LIMIT 1`)
 
-	if !rows.Next() {
+	err = row.Scan(&version)
+	if err == sql.ErrNoRows {
 		dbase.upgrader.logCallback("initiate version", dbase.DbName)
-		_, err = dbase.db.Exec(`INSERT INTO _db.schema(version) VALUES(0)`)
-		if err != nil {
-			return
-		}
+		err = dbase.appendSchemaVersion(0)
 	}
 
 	return
@@ -94,6 +111,7 @@ func (dbase Database) version() (version int, err error) {// {{{
 	return
 }// }}}
 
+// AddDatabase sets a database up for the Run() function with verifying/creating the _db.schema table.
 func (upgrader Upgrader) AddDatabase(host string, port int, dbName, user, pass string) (err error) {// {{{
 	var db Database
 	if db, err = newDatabase(host, port, dbName, user, pass); err != nil {
@@ -110,6 +128,7 @@ func (upgrader Upgrader) AddDatabase(host string, port int, dbName, user, pass s
 	err = db.verifySchemaEntry()
 	return
 }// }}}
+// Run executes the actual schema updates until there are no more available.
 func (upgrader Upgrader) Run() (err error) {// {{{
 	var version int
 
@@ -131,11 +150,7 @@ func (upgrader Upgrader) Run() (err error) {// {{{
 			if _, err = dbase.db.Exec(string(sql)); err != nil {
 				return
 			}
-			_, err = dbase.db.Exec(`
-				INSERT INTO _db.schema(version)
-				VALUES($1)
-			`, version)
-			if err != nil {
+			if err = dbase.appendSchemaVersion(version); err != nil {
 				return
 			}
 		}