Cache the tags on the database

config.go

@@ -1,22 +1,25 @@
 package main
 
 const (
-	PORT              = "8080"
-	DB_IP             = "127.0.0.1"
-	DB_NAME           = "trantor"
-	BOOKS_COLL        = "books"
-	USERS_COLL        = "users"
-	PASS_SALT         = "ImperialLibSalt"
-	TAGS_DISPLAY      = 50
-	SEARCH_ITEMS_PAGE = 20
-	NEW_ITEMS_PAGE    = 50
-	TEMPLATE_PATH     = "templates/"
-	BOOKS_PATH        = "books/"
-	COVER_PATH        = "cover/"
-	NEW_PATH          = "new/"
-	CSS_PATH          = "css/"
-	JS_PATH           = "js/"
-	IMG_PATH          = "img/"
-	RESIZE_CMD        = "/usr/bin/convert -resize 300 -quality 60 "
-	RESIZE_THUMB_CMD  = "/usr/bin/convert -resize 60 -quality 60 "
+	PORT                = "8080"
+	DB_IP               = "127.0.0.1"
+	DB_NAME             = "trantor"
+	META_COLL           = "meta"
+	BOOKS_COLL          = "books"
+	TAGS_COLL           = "tags"
+	USERS_COLL          = "users"
+	PASS_SALT           = "ImperialLibSalt"
+	MINUTES_UPDATE_TAGS = 10
+	TAGS_DISPLAY        = 50
+	SEARCH_ITEMS_PAGE   = 20
+	NEW_ITEMS_PAGE      = 50
+	TEMPLATE_PATH       = "templates/"
+	BOOKS_PATH          = "books/"
+	COVER_PATH          = "cover/"
+	NEW_PATH            = "new/"
+	CSS_PATH            = "css/"
+	JS_PATH             = "js/"
+	IMG_PATH            = "img/"
+	RESIZE_CMD          = "/usr/bin/convert -resize 300 -quality 60 "
+	RESIZE_THUMB_CMD    = "/usr/bin/convert -resize 60 -quality 60 "
 )

database.go

@@ -4,7 +4,11 @@ import (
 	"crypto/md5"
 	"labix.org/v2/mgo"
 	"labix.org/v2/mgo/bson"
-	"sort"
+	"time"
+)
+
+const (
+	META_TYPE_TAGS = "tags updated"
 )
 
 var db *DB
@@ -35,7 +39,9 @@ type Book struct {
 
 type DB struct {
 	session *mgo.Session
+	meta    *mgo.Collection
 	books   *mgo.Collection
+	tags    *mgo.Collection
 	user    *mgo.Collection
 }
 
@@ -48,7 +54,9 @@ func initDB() *DB {
 	}
 
 	database := d.session.DB(DB_NAME)
+	d.meta = database.C(META_COLL)
 	d.books = database.C(BOOKS_COLL)
+	d.tags = database.C(TAGS_COLL)
 	d.user = database.C(USERS_COLL)
 	return d
 }
@@ -169,25 +177,25 @@ func (d *DB) BookActive(id bson.ObjectId) bool {
 	return book.Active
 }
 
-type tagsList []struct {
-	Subject string "_id"
-	Count   int    "value"
+func (d *DB) areTagsOutdated() bool {
+	var result struct {
+		Id bson.ObjectId `bson:"_id"`
+	}
+	err := d.meta.Find(bson.M{"type": META_TYPE_TAGS}).One(&result)
+	if err != nil {
+		return true
+	}
+
+	lastUpdate := result.Id.Time()
+	return time.Since(lastUpdate).Minutes() > MINUTES_UPDATE_TAGS
 }
 
-func (t tagsList) Len() int {
-	return len(t)
-}
-func (t tagsList) Less(i, j int) bool {
-	return t[i].Count > t[j].Count
-}
-func (t tagsList) Swap(i, j int) {
-	aux := t[i]
-	t[i] = t[j]
-	t[j] = aux
-}
+func (d *DB) updateTags() error {
+	_, err := d.meta.RemoveAll(bson.M{"type": META_TYPE_TAGS})
+	if err != nil {
+		return err
+	}
 
-func (d *DB) GetTags() (tagsList, error) {
-	// TODO: cache the tags
 	var mr mgo.MapReduce
 	mr.Map = "function() { " +
 		"if (this.active) { this.subject.forEach(function(s) { emit(s, 1); }); }" +
@@ -197,10 +205,33 @@ func (d *DB) GetTags() (tagsList, error) {
 		"vals.forEach(function() { count += 1; });" +
 		"return count;" +
 		"}"
-	var result tagsList
-	_, err := d.books.Find(bson.M{"active": true}).MapReduce(&mr, &result)
-	if err == nil {
-		sort.Sort(result)
+	mr.Out = bson.M{"replace": TAGS_COLL}
+	_, err = d.books.Find(bson.M{"active": true}).MapReduce(&mr, nil)
+	if err != nil {
+		return err
 	}
-	return result, err
+
+	return d.meta.Insert(bson.M{"type": META_TYPE_TAGS})
+}
+
+func (d *DB) GetTags(numTags int) ([]string, error) {
+	if d.areTagsOutdated() {
+		err := d.updateTags()
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	var result []struct {
+		Tag string "_id"
+	}
+	err := d.tags.Find(nil).Sort("-value").Limit(numTags).All(&result)
+	if err != nil {
+		return nil, err
+	}
+	tags := make([]string, len(result))
+	for i, r := range result {
+		tags[i] = r.Tag
+	}
+	return tags, nil
 }

trantor.go

@@ -82,24 +82,7 @@ type indexData struct {
 func indexHandler(w http.ResponseWriter, r *http.Request) {
 	var data indexData
 
-	/* get the tags */
-	tags, err := db.GetTags()
-	if err == nil {
-		length := len(tags)
-		if length > TAGS_DISPLAY {
-			length = TAGS_DISPLAY
-		}
-		data.Tags = make([]string, length)
-		for i, tag := range tags {
-			if i == TAGS_DISPLAY {
-				break /* display only 50 */
-			}
-			if tag.Subject != "" {
-				data.Tags[i] = tag.Subject
-			}
-		}
-	}
-
+	data.Tags, _ = db.GetTags(TAGS_DISPLAY)
 	data.S = GetStatus(w, r)
 	data.S.Home = true
 	data.Books, data.Count, _ = db.GetBooks(bson.M{"active": true}, 6)