[misc] track redis pub/sub payload sizes on publish

services/real-time/app.coffee

@@ -163,10 +163,13 @@ if Settings.continualPubsubTraffic
 		checker = new HealthCheckManager(channel)
 		logger.debug {channel:channel}, "sending pub to keep connection alive"
 		json = JSON.stringify({health_check:true, key: checker.id, date: new Date().toString()})
+		Metrics.summary "redis.publish.#{channel}", json.length
 		pubsubClient.publish channel, json, (err)->
 			if err?
 				logger.err {err, channel}, "error publishing pubsub traffic to redis"
-			clusterClient.publish "cluster-continual-traffic", {keep: "alive"}, callback
+			blob = JSON.stringify({keep: "alive"})
+			Metrics.summary "redis.publish.cluster-continual-traffic", blob.length
+			clusterClient.publish "cluster-continual-traffic", blob, callback
 
 
 	runPubSubTraffic = ->

services/real-time/app/coffee/ChannelManager.coffee

@@ -48,6 +48,7 @@ module.exports = ChannelManager =
             metrics.inc "unsubscribe.#{baseChannel}"
 
     publish: (rclient, baseChannel, id, data) ->
+        metrics.summary "redis.publish.#{baseChannel}", data.length
         if id is 'all' or !settings.publishOnIndividualChannels
             channel = baseChannel
         else

services/real-time/test/unit/coffee/ChannelManagerTests.coffee

@@ -10,7 +10,7 @@ describe 'ChannelManager', ->
 		@other_rclient = {}
 		@ChannelManager = SandboxedModule.require modulePath, requires:
 			"settings-sharelatex": @settings = {}
-			"metrics-sharelatex": @metrics = {inc: sinon.stub()}
+			"metrics-sharelatex": @metrics = {inc: sinon.stub(), summary: sinon.stub()}
 			"logger-sharelatex": @logger = { log: sinon.stub(), warn: sinon.stub(), error: sinon.stub() }
 	
 	describe "subscribe", ->
@@ -106,3 +106,13 @@ describe 'ChannelManager', ->
 					@rclient.publish.calledWithExactly("applied-ops:1234567890abcdef", "random-message").should.equal true
 					@rclient.publish.calledOnce.should.equal true
 
+		describe "metrics", ->
+			beforeEach ->
+				@rclient.publish = sinon.stub()
+				@ChannelManager.publish @rclient, "applied-ops", "all", "random-message"
+
+			it "should track the payload size", ->
+				@metrics.summary.calledWithExactly(
+					"redis.publish.applied-ops",
+					"random-message".length
+				).should.equal true