Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/4047#discussion_r23980371
--- Diff:
mllib/src/main/scala/org/apache/spark/mllib/impl/PeriodicGraphCheckpointer.scala
---
@@ -0,0 +1,168 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.mllib.impl
+
+import scala.collection.mutable
+
+import org.apache.hadoop.fs.{Path, FileSystem}
+
+import org.apache.spark.Logging
+import org.apache.spark.graphx.Graph
+import org.apache.spark.storage.StorageLevel
+
+
+/**
+ * This class helps with persisting and checkpointing Graphs.
+ *
+ * This class maintains a FIFO queue of Graphs, each of which is persisted
and some of which are
+ * checkpointed. Once one Graph has been checkpointed, then previous RDDs
are unpersisted and their
+ * checkpoint files are removed.
+ *
+ * Users should call [[PeriodicGraphCheckpointer.updateGraph()]] when a
new graph has been created,
+ * before the graph has been materialized. When called, this does the
following:
--- End diff --
Should users be responsible for materializing graphs? If users doesn't
materialize graphs, then `removeCheckpointFile` will happen before the RDDs get
checkpointed.
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