support scan operations on redis cluster

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

@@ -2,6 +2,7 @@ Settings = require "settings-sharelatex"
 redis = require("redis-sharelatex")
 rclient = redis.createClient(Settings.redis.history)
 Keys = Settings.redis.history.key_schema
+async = require "async"
 
 module.exports = RedisManager =
 
@@ -33,12 +34,19 @@ module.exports = RedisManager =
 		rclient.smembers Keys.docsWithHistoryOps({project_id}), callback
 
 	# iterate over keys asynchronously using redis scan (non-blocking)
+	# handle all the cluster nodes or single redis server
 	_getKeys: (pattern, callback) ->
+		nodes = rclient.nodes?('master') || [ rclient ];
+		doKeyLookupForNode = (node, cb) ->
+			RedisManager._getKeysFromNode node, pattern, cb
+		async.concatSeries nodes, doKeyLookupForNode, callback
+
+	_getKeysFromNode: (node, pattern, callback) ->
 		cursor = 0  # redis iterator
 		keySet = {} # use hash to avoid duplicate results
 		# scan over all keys looking for pattern
 		doIteration = (cb) ->
-			rclient.scan cursor, "MATCH", pattern, "COUNT", 1000, (error, reply) ->
+			node.scan cursor, "MATCH", pattern, "COUNT", 1000, (error, reply) ->
 				return callback(error) if error?
 				[cursor, keys] = reply
 				for key in keys
@@ -50,21 +58,20 @@ module.exports = RedisManager =
 		doIteration()
 
 	# extract ids from keys like DocsWithHistoryOps:57fd0b1f53a8396d22b2c24b
+	# or DocsWithHistoryOps:{57fd0b1f53a8396d22b2c24b} (for redis cluster)
 	_extractIds: (keyList) ->
-		ids = (key.split(":")[1] for key in keyList)
+		ids = for key in keyList
+			m = key.match(/:\{?([0-9a-f]{24})\}?/) # extract object id
+			m[1]
 		return ids
 
-	# this will only work on single node redis, not redis cluster
 	getProjectIdsWithHistoryOps: (callback = (error, project_ids) ->) ->
-		return callback(new Error("not supported")) if rclient.nodes?
 		RedisManager._getKeys Keys.docsWithHistoryOps({project_id:"*"}), (error, project_keys) ->
 			return callback(error) if error?
 			project_ids = RedisManager._extractIds project_keys
 			callback(error, project_ids)
 
-	# this will only work on single node redis, not redis cluster
 	getAllDocIdsWithHistoryOps: (callback = (error, doc_ids) ->) ->
-		return callback(new Error("not supported")) if rclient.nodes?
 		# return all the docids, to find dangling history entries after
 		# everything is flushed.
 		RedisManager._getKeys Keys.uncompressedHistoryOps({doc_id:"*"}), (error, doc_keys) ->