From 69934dcd950f74c2757e2f30e5de2abcb2419215 Mon Sep 17 00:00:00 2001
From: Dominique Lefevre <domingolefevre@gmail.com>
Date: Fri, 4 Jul 2025 14:11:46 +0300
Subject: [PATCH] Make fewer allocations in QueryContext().

For a simple query like `SELECT * FROM t WHERE id = $1`,
QueryContext() used to make 6 allocations on average.
Reduce that to 4 by avoiding two allocations that
are immediately discarded:

  // the variadic arguments of c.conn.Query() escape,
  // so args is heap-allocated
  args := []any{databaseSQLResultFormats}
  // append() reallocates args to add enough space +
  // an array returned by namedValueToInterface()
  // is immediately discarded
  args = append(args, namedValueToInterface(argsV)...)
---
 stdlib/sql.go | 30 +++++++++---------------------
 1 file changed, 9 insertions(+), 21 deletions(-)

diff --git a/stdlib/sql.go b/stdlib/sql.go
index 4924fe41a..939b9636d 100644
--- a/stdlib/sql.go
+++ b/stdlib/sql.go
@@ -471,7 +471,8 @@ func (c *Conn) ExecContext(ctx context.Context, query string, argsV []driver.Nam
 		return nil, driver.ErrBadConn
 	}
 
-	args := namedValueToInterface(argsV)
+	args := make([]any, len(argsV))
+	convertNamedArguments(args, argsV)
 
 	commandTag, err := c.conn.Exec(ctx, query, args...)
 	// if we got a network error before we had a chance to send the query, retry
@@ -488,8 +489,9 @@ func (c *Conn) QueryContext(ctx context.Context, query string, argsV []driver.Na
 		return nil, driver.ErrBadConn
 	}
 
-	args := []any{databaseSQLResultFormats}
-	args = append(args, namedValueToInterface(argsV)...)
+	args := make([]any, 1+len(argsV))
+	args[0] = databaseSQLResultFormats
+	convertNamedArguments(args[1:], argsV)
 
 	rows, err := c.conn.Query(ctx, query, args...)
 	if err != nil {
@@ -848,28 +850,14 @@ func (r *Rows) Next(dest []driver.Value) error {
 	return nil
 }
 
-func valueToInterface(argsV []driver.Value) []any {
-	args := make([]any, 0, len(argsV))
-	for _, v := range argsV {
-		if v != nil {
-			args = append(args, v.(any))
-		} else {
-			args = append(args, nil)
-		}
-	}
-	return args
-}
-
-func namedValueToInterface(argsV []driver.NamedValue) []any {
-	args := make([]any, 0, len(argsV))
-	for _, v := range argsV {
+func convertNamedArguments(args []any, argsV []driver.NamedValue) {
+	for i, v := range argsV {
 		if v.Value != nil {
-			args = append(args, v.Value.(any))
+			args[i] = v.Value.(any)
 		} else {
-			args = append(args, nil)
+			args[i] = nil
 		}
 	}
-	return args
 }
 
 type wrapTx struct {