 		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) ->

redis = require("redis-sharelatex")
rclient = redis.createClient(Settings.redis.history)
Keys = Settings.redis.history.key_schema

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) ->
			node.scan cursor, "MATCH", pattern, "COUNT", 1000, (error, reply) ->
				return callback(error) if error?
				[cursor, keys] = reply
				for key in keys
