From 2ef550bc274cae44654a7c32a49af0d2e59451d4 Mon Sep 17 00:00:00 2001
From: Danny van Kooten <dannyvankooten@gmail.com>
Date: Sun, 15 Jul 2018 10:05:03 +0200
Subject: [PATCH] reduce number of memory allocations in hot path

---
 pkg/api/collect.go                  | 18 +++++++++---------
 pkg/datastore/sqlstore/pageviews.go | 25 ++++++++++++++++++++-----
 2 files changed, 29 insertions(+), 14 deletions(-)

diff --git a/pkg/api/collect.go b/pkg/api/collect.go
index c38a8a5..c34bc57 100644
--- a/pkg/api/collect.go
+++ b/pkg/api/collect.go
@@ -153,9 +153,9 @@ func aggregate(db datastore.Datastore) {
 }
 
 func collect(db datastore.Datastore, pageviews chan *models.Pageview) {
-	var buffer []*models.Pageview
 	var size = 800
 	var timeout = 600 * time.Millisecond
+	var buffer = make([]*models.Pageview, 0)
 
 	for {
 		select {
@@ -163,12 +163,12 @@ func collect(db datastore.Datastore, pageviews chan *models.Pageview) {
 			buffer = append(buffer, pageview)
 			if len(buffer) >= size {
 				persist(db, buffer)
-				buffer = buffer[:0]
+				buffer = make([]*models.Pageview, 0)
 			}
 		case <-time.After(timeout):
 			if len(buffer) > 0 {
 				persist(db, buffer)
-				buffer = buffer[:0]
+				buffer = make([]*models.Pageview, 0)
 			}
 		}
 	}
@@ -179,11 +179,11 @@ func persist(db datastore.Datastore, pageviews []*models.Pageview) {
 	updates := make([]*models.Pageview, 0, n)
 	inserts := make([]*models.Pageview, 0, n)
 
-	for _, p := range pageviews {
-		if !p.IsBounce {
-			updates = append(updates, p)
+	for i := range pageviews {
+		if !pageviews[i].IsBounce {
+			updates = append(updates, pageviews[i])
 		} else {
-			inserts = append(inserts, p)
+			inserts = append(inserts, pageviews[i])
 		}
 	}
 
@@ -192,11 +192,11 @@ func persist(db datastore.Datastore, pageviews []*models.Pageview) {
 	var err error
 	err = db.InsertPageviews(inserts)
 	if err != nil {
-		log.Error(err)
+		log.Errorf("error inserting pageviews: %s", err)
 	}
 
 	err = db.UpdatePageviews(updates)
 	if err != nil {
-		log.Error(err)
+		log.Errorf("error updating pageviews: %s", err)
 	}
 }
diff --git a/pkg/datastore/sqlstore/pageviews.go b/pkg/datastore/sqlstore/pageviews.go
index 4b963c1..c1506b1 100644
--- a/pkg/datastore/sqlstore/pageviews.go
+++ b/pkg/datastore/sqlstore/pageviews.go
@@ -36,12 +36,27 @@ func (db *sqlstore) InsertPageviews(pageviews []*models.Pageview) error {
 	placeholders := strings.Repeat("(?, ?, ?, ?, ?, ?, ?, ?, ?, ?),", n)
 	placeholders = placeholders[:len(placeholders)-1]
 
-	// generate values slice
-	values := make([]interface{}, 0, n*10)
-	for i := 0; i < n; i++ {
-		values = append(values, pageviews[i].ID, pageviews[i].Hostname, pageviews[i].Pathname, pageviews[i].IsNewVisitor, pageviews[i].IsNewSession, pageviews[i].IsUnique, pageviews[i].IsBounce, pageviews[i].Referrer, pageviews[i].Duration, pageviews[i].Timestamp)
+	// init values slice with correct length
+	nValues := n * 10
+	values := make([]interface{}, nValues)
+
+	// overwrite nil values in slice
+	j := 0
+	for i := range pageviews {
+		j = i * 10
+		values[j] = pageviews[i].ID
+		values[j+1] = pageviews[i].Hostname
+		values[j+2] = pageviews[i].Pathname
+		values[j+3] = pageviews[i].IsNewVisitor
+		values[j+4] = pageviews[i].IsNewSession
+		values[j+5] = pageviews[i].IsUnique
+		values[j+6] = pageviews[i].IsBounce
+		values[j+7] = pageviews[i].Referrer
+		values[j+8] = pageviews[i].Duration
+		values[j+9] = pageviews[i].Timestamp
 	}
 
+	// string together query & execute with values
 	query := `INSERT INTO pageviews(id, hostname, pathname, is_new_visitor, is_new_session, is_unique, is_bounce, referrer, duration, timestamp) VALUES ` + placeholders
 	query = db.Rebind(query)
 	_, err := db.Exec(query, values...)
@@ -69,7 +84,7 @@ func (db *sqlstore) UpdatePageviews(pageviews []*models.Pageview) error {
 		return err
 	}
 
-	for i := 0; i < len(pageviews); i++ {
+	for i := range pageviews {
 		_, err = stmt.Exec(query, pageviews[i].IsBounce, pageviews[i].Duration)
 	}