Use Raw MySQL packets when passing results back from VTTablet to VTGate

go/mathstats/ewma.go

@@ -0,0 +1,58 @@
+/*
+Copyright 2024 The Vitess Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package mathstats
+
+import (
+	"math"
+	"sync/atomic"
+)
+
+type SimpleEWMA struct {
+	// The current value of the average. After adding with Add(), this is
+	// updated to reflect the average of all values seen thus far.
+	value atomic.Uint64
+}
+
+// Add adds a value to the series and updates the moving average.
+func (e *SimpleEWMA) Add(value uint64) {
+	const (
+		AVG_METRIC_AGE float64 = 30.0
+		DECAY          float64 = 2 / (float64(AVG_METRIC_AGE) + 1)
+	)
+
+	fvalue := float64(value)
+
+	for {
+		v := e.value.Load()
+
+		var nv float64
+		if v == 0 {
+			nv = fvalue
+		} else {
+			nv = (fvalue * DECAY) + (math.Float64frombits(v) * (1 - DECAY))
+		}
+
+		if e.value.CompareAndSwap(v, math.Float64bits(nv)) {
+			return
+		}
+	}
+}
+
+// Value returns the current value of the moving average.
+func (e *SimpleEWMA) Value() uint64 {
+	return uint64(math.Float64frombits(e.value.Load()))
+}

go/mysql/conn.go

@@ -409,6 +409,38 @@ func (c *Conn) readHeaderFrom(r io.Reader) (int, error) {
 	return int(uint32(c.header[0]) | uint32(c.header[1])<<8 | uint32(c.header[2])<<16), nil
 }
 
+func (c *Conn) readPacketAsProto(b *queryResultBuilder) ([]byte, error) {
+	r := c.getReader()
+
+	length, err := c.readHeaderFrom(r)
+	if err != nil {
+		return nil, err
+	}
+
+	if length == 0 {
+		// This can be caused by the packet after a packet of
+		// exactly size MaxPacketSize.
+		return nil, nil
+	}
+
+	// Use the bufPool.
+	if length < MaxPacketSize {
+		buf := b.Packet(length)
+		if _, err := io.ReadFull(r, buf); err != nil {
+			return nil, vterrors.Wrapf(err, "io.ReadFull(packet body of length %v) failed", length)
+		}
+		return buf, nil
+	}
+
+	// This packet came from MySQL, so how is it sending us a packet
+	// that's beyond the max size???
+
+	// Much slower path, revert to allocating everything from scratch.
+	// We're going to concatenate a lot of data anyway, can't really
+	// optimize this code path easily.
+	panic("TODO: large packets")
+}
+
 // readEphemeralPacket attempts to read a packet into buffer from sync.Pool.  Do
 // not use this method if the contents of the packet needs to be kept
 // after the next readEphemeralPacket.