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https://issues.apache.org/jira/browse/ZOOKEEPER-2872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16131747#comment-16131747
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Hudson commented on ZOOKEEPER-2872:
-----------------------------------
SUCCESS: Integrated in Jenkins build ZooKeeper-trunk #3503 (See
[https://builds.apache.org/job/ZooKeeper-trunk/3503/])
ZOOKEEPER-2872: Interrupted snapshot sync causes data loss (hanm: rev
0706b40afad079f19fe9f76c99bbb7ec69780dbd)
* (edit) src/java/test/org/apache/zookeeper/server/quorum/Zab1_0Test.java
* (edit) src/java/test/org/apache/zookeeper/test/TruncateTest.java
* (edit) src/java/main/org/apache/zookeeper/server/quorum/Learner.java
* (edit) src/java/main/org/apache/zookeeper/server/persistence/SnapShot.java
* (edit) src/java/main/org/apache/zookeeper/server/persistence/FileSnap.java
* (edit) src/java/main/org/apache/zookeeper/server/ZooKeeperServer.java
* (edit)
src/java/main/org/apache/zookeeper/server/persistence/FileTxnSnapLog.java
> Interrupted snapshot sync causes data loss
> ------------------------------------------
>
> Key: ZOOKEEPER-2872
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2872
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.4.10, 3.5.3, 3.6.0
> Reporter: Brian Nixon
>
> There is a way for observers to permanently lose data from their local data
> tree while remaining members of good standing with the ensemble and
> continuing to serve client traffic when the following chain of events occurs.
> 1. The observer dies in epoch N from machine failure.
> 2. The observer comes back up in epoch N+1 and requests a snapshot sync to
> catch up.
> 3. The machine powers off before the snapshot is synced to disc and after
> some txn's have been logged (depending on the OS, this can happen!).
> 4. The observer comes back a second time and replays its most recent snapshot
> (epoch <= N) as well as the txn logs (epoch N+1).
> 5. A diff sync is requested from the leader and the observer broadcasts
> availability.
> In this scenario, any commits from epoch N that the observer did not receive
> before it died the first time will never be exposed to the observer and no
> part of the ensemble will complain.
> This situation is not unique to observers and can happen to any learner. As a
> simple fix, fsync-ing the snapshots received from the leader will avoid the
> case of missing snapshots causing data loss.
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