added a /pack endpoint to fork a pack worker

services/track-changes/app.coffee

@@ -7,6 +7,8 @@ Metrics = require "metrics-sharelatex"
 Metrics.initialize("track-changes")
 Metrics.mongodb.monitor(Path.resolve(__dirname + "/node_modules/mongojs/node_modules/mongodb"), logger)
 
+child_process = require "child_process"
+
 HttpController = require "./app/js/HttpController"
 express = require "express"
 app = express()
@@ -25,6 +27,19 @@ app.post "/project/:project_id/doc/:doc_id/version/:version/restore", HttpContro
 
 app.post "/doc/:doc_id/pack", HttpController.packDoc
 
+packWorker = null # use a single packing worker
+
+app.post "/pack", (req, res, next) ->
+	if packWorker?
+		res.send "pack already running"
+	else
+		logger.log "running pack"
+		packWorker = child_process.fork(__dirname + '/app/js/PackWorker.js')
+		packWorker.on 'exit', (code, signal) ->
+			logger.log {code, signal}, "history auto pack exited"
+			packWorker = null
+		res.send "pack started"
+
 app.get "/status", (req, res, next) ->
 	res.send "track-changes is alive"
 

services/track-changes/app/coffee/PackWorker.coffee

@@ -0,0 +1,60 @@
+async = require "async"
+_ = require "underscore"
+{db, ObjectId} = require "./mongojs"
+BSON=db.bson.BSON
+logger = require "logger-sharelatex"
+logger.initialize("track-changes-packworker")
+LockManager = require "./LockManager"
+PackManager = require "./PackManager"
+
+# this worker script is forked by the main process to look for
+# document histories which can be packed
+
+DOCUMENT_PACK_DELAY = 1000
+
+logger.log 'checking for updates'
+
+finish = () ->
+	logger.log 'closing db'
+	db.close () ->
+		logger.log 'exiting from pack worker'
+		process.exit()
+
+processUpdates = (pending) ->
+	async.eachSeries pending,	(doc_id, callback) ->
+		PackManager.packDocHistory doc_id, (err, result) ->
+			if err?
+				logger.error {err, result}, "error in pack worker"
+				return callback(err)
+			setTimeout () ->
+				callback(err, result)
+			, DOCUMENT_PACK_DELAY
+	, (err, results) ->
+		if err?
+			logger.error {err}, 'error in pack worker processUpdates'
+		finish()
+
+# find the documents which can be packed, by checking the number of
+# unpacked updates in the docHistoryStats collection
+
+db.docHistoryStats.find({
+	update_count: {$gt : PackManager.MIN_COUNT}
+}).sort({
+	update_count:-1
+}).limit 1000, (err, results) ->
+	if err?
+		logger.log {err}, 'error checking for updates'
+		finish()
+		return
+	results = _.filter results, (doc) ->
+		if doc.last_checked? and doc.last_checked > doc.last_update
+			# skip documents which don't have any updates since last check
+			return false
+		else if doc.last_packed? and doc.last_packed > doc.last_update
+			# skip documents which don't have any updates since last pack
+			return false
+		else
+			return true
+	pending = _.pluck results, 'doc_id'
+	logger.log "found #{pending.length} documents to pack"
+	processUpdates pending