From 8b365ce37e04c661320dff233e8d7e4b7675fc3a Mon Sep 17 00:00:00 2001
From: Jack Christensen <jack@jackchristensen.com>
Date: Sat, 4 May 2019 11:01:09 -0500
Subject: [PATCH] Extract int16SlicePool

---
 conn.go             | 20 +++++---------------
 int16_slice_pool.go | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+), 15 deletions(-)
 create mode 100644 int16_slice_pool.go

diff --git a/conn.go b/conn.go
index 629aafad..6bfe515d 100644
--- a/conn.go
+++ b/conn.go
@@ -49,9 +49,8 @@ type Conn struct {
 
 	wbuf             []byte
 	preallocatedRows []connRows
-	paramFormats     []int16
+	int16SlicePool   int16SlicePool
 	paramValues      [][]byte
-	resultFormats    []int16
 }
 
 // PreparedStatement is a description of a prepared statement
@@ -160,9 +159,7 @@ func connect(ctx context.Context, config *ConnConfig) (c *Conn, err error) {
 	c.doneChan = make(chan struct{})
 	c.closedChan = make(chan error)
 	c.wbuf = make([]byte, 0, 1024)
-	c.paramFormats = make([]int16, 0, 16)
 	c.paramValues = make([][]byte, 0, 16)
-	c.resultFormats = make([]int16, 0, 32)
 
 	// Replication connections can't execute the queries to
 	// populate the c.PgTypes and c.pgsqlAfInet
@@ -651,12 +648,7 @@ optionLoop:
 		return rows, rows.err
 	}
 
-	var paramFormats []int16
-	if len(args) > cap(c.paramFormats) {
-		paramFormats = make([]int16, len(args))
-	} else {
-		paramFormats = c.paramFormats[:len(args)]
-	}
+	paramFormats := c.int16SlicePool.get(len(args))
 
 	var paramValues [][]byte
 	if len(args) > cap(c.paramValues) {
@@ -682,11 +674,7 @@ optionLoop:
 	}
 
 	if resultFormats == nil {
-		if len(ps.FieldDescriptions) > cap(c.resultFormats) {
-			resultFormats = make([]int16, len(ps.FieldDescriptions))
-		} else {
-			resultFormats = c.resultFormats[:len(ps.FieldDescriptions)]
-		}
+		resultFormats = c.int16SlicePool.get(len(ps.FieldDescriptions))
 
 		for i := range resultFormats {
 			if dt, ok := c.ConnInfo.DataTypeForOID(ps.FieldDescriptions[i].DataType); ok {
@@ -701,6 +689,8 @@ optionLoop:
 
 	rows.resultReader = c.pgConn.ExecPrepared(ctx, ps.Name, paramValues, paramFormats, resultFormats)
 
+	c.int16SlicePool.reset()
+
 	return rows, rows.err
 }
 
diff --git a/int16_slice_pool.go b/int16_slice_pool.go
new file mode 100644
index 00000000..2e7c3939
--- /dev/null
+++ b/int16_slice_pool.go
@@ -0,0 +1,42 @@
+package pgx
+
+const int16SlicePoolSizeStep = 16
+
+type int16SlicePool struct {
+	buf        []int16
+	pos        int
+	allocCount int
+	resetCount int
+}
+
+func (p *int16SlicePool) get(n int) []int16 {
+	if n > len(p.buf[p.pos:]) {
+		growthStep := ((n / int16SlicePoolSizeStep) + 1) * int16SlicePoolSizeStep
+		p.buf = make([]int16, len(p.buf)+growthStep)
+		p.pos = 0
+	}
+
+	result := p.buf[p.pos : p.pos+n]
+	p.pos += n
+
+	p.allocCount += n
+
+	return result
+}
+
+func (p *int16SlicePool) reset() {
+	p.pos = 0
+	p.resetCount += 1
+
+	if p.resetCount == 128 {
+		allocsPerReset := p.allocCount / p.resetCount
+		maxSize := allocsPerReset + (int16SlicePoolSizeStep * 4)
+
+		if len(p.buf) > maxSize {
+			p.buf = make([]int16, maxSize)
+		}
+
+		p.allocCount = 0
+		p.resetCount = 0
+	}
+}