Github user d2r commented on a diff in the pull request:
https://github.com/apache/storm/pull/845#discussion_r45789625
--- Diff:
storm-core/src/jvm/backtype/storm/blobstore/KeySequenceNumber.java ---
@@ -0,0 +1,227 @@
+/**
+ * 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 backtype.storm.blobstore;
+
+import backtype.storm.nimbus.NimbusInfo;
+import backtype.storm.utils.Utils;
+import org.apache.curator.framework.CuratorFramework;
+import org.apache.zookeeper.CreateMode;
+import org.apache.zookeeper.ZooDefs;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.nio.ByteBuffer;
+import java.util.TreeSet;
+import java.util.Map;
+import java.util.List;
+
+/**
+ * Class hands over the key sequence number which implies the number of
updates made to a blob.
+ * The information regarding the keys and the sequence number which
represents the number of updates are
+ * stored within the zookeeper in the following format.
+ * /storm/blobstore/key_name/nimbushostport-sequencenumber
+ * Example:
+ * If there are two nimbodes with nimbus.seeds:leader,non-leader are set,
+ * then the state inside the zookeeper is eventually stored as:
+ * /storm/blobstore/key1/leader:8080-1
+ * /storm/blobstore/key1/non-leader:8080-1
+ * indicates that a new blob with the name key1 has been created on the
leader
+ * nimbus and the non-leader nimbus syncs after a call back is triggered
by attempting
+ * to download the blob and finally updates its state inside the zookeeper.
+ *
+ * A watch is placed on the /storm/blobstore/key1 and the znodes
leader:8080-1 and
+ * non-leader:8080-1 are ephemeral which implies that these nodes exist
only until the
+ * connection between the corresponding nimbus and the zookeeper persist.
If in case the
+ * nimbus crashes the node disappears under /storm/blobstore/key1.
+ *
+ * The sequence number for the keys are handed over based on the following
scenario:
+ * Lets assume there are three nimbodes up and running, one being the
leader and the other
+ * being the non-leader.
+ *
+ * 1. Create is straight forward.
+ * Check whether the znode -> /storm/blobstore/key1 has been created or
not. It implies
+ * the blob has not been created yet. If not created, it creates it and
updates the zookeeper
+ * states under /storm/blobstore/key1 and
/storm/blobstoremaxkeysequencenumber/key1.
+ * The znodes it creates on these nodes are
/storm/blobstore/key1/leader:8080-1,
+ * /storm/blobstore/key1/non-leader:8080-1 and
/storm/blobstoremaxkeysequencenumber/key1/1.
+ * The later holds the global sequence number across all nimbodes more
like a static variable
--- End diff --
Really nice documentation here!
`later` -> `latter`
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at infrastruct...@apache.org or file a JIRA ticket
with INFRA.
---
