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https://issues.apache.org/jira/browse/ZOOKEEPER-3056?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16506598#comment-16506598
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Michael Han commented on ZOOKEEPER-3056:
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I agree we should try providing a seamless upgrade path.
[~nixon] What do you think about my previous proposal on the signal file? I
think it's pretty similar with the initialization marker file you introduced in
ZK-261 whose presence indicate trust empty DB or not. The signal file's
presence indicate trust of the transaction log alone or not (or, ignore the -1L
== deserializeResult check or not).
This is like an automatic flag to turn on / off the deserializeResult check by
ZK itself.
> Fails to load database with missing snapshot file but valid transaction log
> file
> --------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-3056
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3056
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.5.3, 3.5.4
> Reporter: Michael Han
> Priority: Critical
>
> [An
> issue|https://lists.apache.org/thread.html/cc17af6ef05d42318f74148f1a704f16934d1253f1472cccc1a93b4b@%3Cdev.zookeeper.apache.org%3E]
> was reported when a user failed to upgrade from 3.4.10 to 3.5.4 with missing
> snapshot file.
> The code complains about missing snapshot file is
> [here|https://github.com/apache/zookeeper/blob/release-3.5.4/src/java/main/org/apache/zookeeper/server/persistence/FileTxnSnapLog.java#L206]
> which is introduced as part of ZOOKEEPER-2325.
> With this check, ZK will not load the db without a snapshot file, even the
> transaction log files are present and valid. This could be a problem for
> restoring a ZK instance which does not have a snapshot file but have a sound
> state (e.g. it crashes before being able to take the first snap shot with a
> large snapCount parameter configured).
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