Cache connection properties in the pool

This is a quick attempt to improve connection startup time by caching
the properties that are loaded when a connection is ready in the pool,
so that further connections don't incur this cost.

I'm not entirely convinced by the interface here, perhaps these 3 items
could live in their own type and that be passed around for clearer code,
but the idea works well.

conn.go

@@ -63,8 +63,8 @@ type Conn struct {
 	logLevel           int
 	mr                 msgReader
 	fp                 *fastpath
-	pgsql_af_inet      byte
+	pgsql_af_inet      *byte
-	pgsql_af_inet6     byte
+	pgsql_af_inet6     *byte
 	busy               bool
 	poolResetCount     int
 	preallocatedRows   []Rows
@@ -137,9 +137,16 @@ func (e ProtocolError) Error() string {
 // config.Host must be specified. config.User will default to the OS user name.
 // Other config fields are optional.
 func Connect(config ConnConfig) (c *Conn, err error) {
+	return connect(config, nil, nil, nil)
+}
+
+func connect(config ConnConfig, pgTypes map[Oid]PgType, pgsql_af_inet *byte, pgsql_af_inet6 *byte) (c *Conn, err error) {
 	c = new(Conn)
 
 	c.config = config
+	c.PgTypes = pgTypes
+	c.pgsql_af_inet = pgsql_af_inet
+	c.pgsql_af_inet6 = pgsql_af_inet6
 
 	if c.config.LogLevel != 0 {
 		c.logLevel = c.config.LogLevel
@@ -283,15 +290,19 @@ func (c *Conn) connect(config ConnConfig, network, address string, tlsConfig *tl
 				c.log(LogLevelInfo, "Connection established")
 			}
 
+			if c.PgTypes == nil {
 				err = c.loadPgTypes()
 				if err != nil {
 					return err
 				}
+			}
 
+			if c.pgsql_af_inet == nil || c.pgsql_af_inet6 == nil {
 				err = c.loadInetConstants()
 				if err != nil {
 					return err
 				}
+			}
 
 			return nil
 		default:
@@ -336,8 +347,8 @@ func (c *Conn) loadInetConstants() error {
 		return err
 	}
 
-	c.pgsql_af_inet = ipv4[0]
+	c.pgsql_af_inet = &ipv4[0]
-	c.pgsql_af_inet6 = ipv6[0]
+	c.pgsql_af_inet6 = &ipv6[0]
 
 	return nil
 }

conn_pool.go

@@ -26,6 +26,9 @@ type ConnPool struct {
 	closed               bool
 	preparedStatements   map[string]*PreparedStatement
 	acquireTimeout       time.Duration
+	pgTypes              map[Oid]PgType
+	pgsql_af_inet        *byte
+	pgsql_af_inet6       *byte
 }
 
 type ConnPoolStat struct {
@@ -244,11 +247,15 @@ func (p *ConnPool) Stat() (s ConnPoolStat) {
 }
 
 func (p *ConnPool) createConnection() (*Conn, error) {
-	c, err := Connect(p.config)
+	c, err := connect(p.config, p.pgTypes, p.pgsql_af_inet, p.pgsql_af_inet6)
 	if err != nil {
 		return nil, err
 	}
 
+	p.pgTypes = c.PgTypes
+	p.pgsql_af_inet = c.pgsql_af_inet
+	p.pgsql_af_inet6 = c.pgsql_af_inet6
+
 	if p.afterConnect != nil {
 		err = p.afterConnect(c)
 		if err != nil {

values.go

@@ -1576,10 +1576,10 @@ func encodeIPNet(w *WriteBuf, oid Oid, value net.IPNet) error {
 	switch len(value.IP) {
 	case net.IPv4len:
 		size = 8
-		family = w.conn.pgsql_af_inet
+		family = *w.conn.pgsql_af_inet
 	case net.IPv6len:
 		size = 20
-		family = w.conn.pgsql_af_inet6
+		family = *w.conn.pgsql_af_inet6
 	default:
 		return fmt.Errorf("Unexpected IP length: %v", len(value.IP))
 	}