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optimize readPacket #1705

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Merged
methane merged 1 commit into go-sql-driver:master from methane:opt-read
Apr 24, 2025
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18 changes: 8 additions & 10 deletions buffer.go
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,11 @@ func (b *buffer) busy() bool {
return len(b.buf) > 0
}

// len returns how many bytes in the read buffer.
func (b *buffer) len() int {
return len(b.buf)
}

// fill reads into the read buffer until at least _need_ bytes are in it.
func (b *buffer) fill(need int, r readerFunc) error {
// we'll move the contents of the current buffer to dest before filling it.
Expand Down Expand Up @@ -86,17 +91,10 @@ func (b *buffer) fill(need int, r readerFunc) error {

// returns next N bytes from buffer.
// The returned slice is only guaranteed to be valid until the next read
func (b *buffer) readNext(need int, r readerFunc) ([]byte, error) {
if len(b.buf) < need {
// refill
if err := b.fill(need, r); err != nil {
return nil, err
}
}

data := b.buf[:need]
func (b *buffer) readNext(need int) []byte {
data := b.buf[:need:need]
b.buf = b.buf[need:]
return data, nil
return data
}

// takeBuffer returns a buffer with the requested size.
Expand Down
12 changes: 6 additions & 6 deletions compress.go
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -84,26 +84,26 @@ func (c *compIO) reset() {
c.buff.Reset()
}

func (c *compIO) readNext(need int, r readerFunc) ([]byte, error) {
func (c *compIO) readNext(need int) ([]byte, error) {
for c.buff.Len() < need {
if err := c.readCompressedPacket(r); err != nil {
if err := c.readCompressedPacket(); err != nil {
return nil, err
}
}
data := c.buff.Next(need)
return data[:need:need], nil // prevent caller writes into c.buff
}

func (c *compIO) readCompressedPacket(r readerFunc) error {
header, err := c.mc.buf.readNext(7, r) // size of compressed header
func (c *compIO) readCompressedPacket() error {
header, err := c.mc.readNext(7)
if err != nil {
return err
}
_ = header[6] // bounds check hint to compiler; guaranteed by readNext

// compressed header structure
comprLength := getUint24(header[0:3])
compressionSequence := uint8(header[3])
compressionSequence := header[3]
uncompressedLength := getUint24(header[4:7])
if debug {
fmt.Printf("uncompress cmplen=%v uncomplen=%v pkt_cmp_seq=%v expected_cmp_seq=%v\n",
Expand All @@ -120,7 +120,7 @@ func (c *compIO) readCompressedPacket(r readerFunc) error {
c.mc.sequence = compressionSequence + 1
c.mc.compressSequence = c.mc.sequence

comprData, err := c.mc.buf.readNext(comprLength, r)
comprData, err := c.mc.readNext(comprLength)
if err != nil {
return err
}
Expand Down
17 changes: 14 additions & 3 deletions packets.go
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Original file line number Diff line number Diff line change
Expand Up @@ -25,19 +25,30 @@ import (
// https://dev.mysql.com/doc/dev/mysql-server/latest/PAGE_PROTOCOL.html
// https://mariadb.com/kb/en/clientserver-protocol/

// read n bytes from mc.buf
func (mc *mysqlConn) readNext(n int) ([]byte, error) {
if mc.buf.len() < n {
err := mc.buf.fill(n, mc.readWithTimeout)
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@methane methane Apr 23, 2025 •
edited
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Go compiler inlines mc.buff.fill. It doesn't allocate mc.readWithTimeout.

It may be possible to rewrite in cleaner code. But I minimise changes to backport this PR to 1.9 branch.

if err != nil {
return nil, err
}
}
return mc.buf.readNext(n), nil
}

// Read packet to buffer 'data'
func (mc *mysqlConn) readPacket() ([]byte, error) {
var prevData []byte
invalidSequence := false

readNext := mc.buf.readNext
readNext := mc.readNext
if mc.compress {
readNext = mc.compIO.readNext
}

for {
// read packet header
data, err := readNext(4, mc.readWithTimeout)
data, err := readNext(4)
Comment on lines -40 to +51
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go compiler allocated mc.readWithTimeout method trampoline object.

if err != nil {
mc.close()
if cerr := mc.canceled.Value(); cerr != nil {
Expand Down Expand Up @@ -85,7 +96,7 @@ func (mc *mysqlConn) readPacket() ([]byte, error) {
}

// read packet body [pktLen bytes]
data, err = readNext(pktLen, mc.readWithTimeout)
data, err = readNext(pktLen)
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ditto.

if err != nil {
mc.close()
if cerr := mc.canceled.Value(); cerr != nil {
Expand Down

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