added lru cache

services/spelling/app/coffee/LearnedWordsManager.coffee

@@ -1,7 +1,18 @@
 db = require("./DB")
+LRU = require("lru-cache")
+cacheOpts = 
+	max: 5000
+	maxAge: 1000 * 60 * 60
+
+cache = LRU(cacheOpts)
+logger = require 'logger-sharelatex'
+metrics = require('metrics-sharelatex')
+
+
 
 module.exports = LearnedWordsManager =
 	learnWord: (user_token, word, callback = (error)->) ->
+		cache.del(user_token)
 		db.spellingPreferences.update {
 			token: user_token
 		}, {
@@ -11,8 +22,19 @@ module.exports = LearnedWordsManager =
 		}, callback
 
 	getLearnedWords: (user_token, callback = (error, words)->) ->
+		cachedWords = cache.get(user_token)
+		if cachedWords
+			logger.info user_token:user_token, "cache hit"
+			metrics.inc "cache-hit", 0.1
+			return callback(null, cachedWords)
+
+		metrics.inc "cache-miss", 0.1
+		logger.info user_token:user_token, "cache miss"
+		
 		db.spellingPreferences.findOne token: user_token, (error, preferences) ->
 			return callback error if error?
-			callback null, (preferences?.learnedWords || [])
+			words = preferences?.learnedWords || []
+			cache.set(user_token, words)
+			callback null, words
 
 		

services/spelling/package.json

@@ -12,6 +12,7 @@
     "body-parser": "^1.12.0",
     "express": "^4.12.1",
     "logger-sharelatex": "git+https://github.com/sharelatex/logger-sharelatex.git#v1.0.0",
+    "lru-cache": "^2.5.0",
     "metrics-sharelatex": "git+https://github.com/sharelatex/metrics-sharelatex.git#v1.0.0",
     "mongojs": "0.9.11",
     "node-statsd": "0.0.3",