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Problem: Issue occurs when ZooKeeper 3.5.5 is trying to load an existing 3.4 data dir in which no snapshot file has been created. This usually happens in standalone mode if txn count hasn't reached the limit of snapshot creation. An extra startup check has been introduced in 3.5.5 (ZOOKEEPER-2325) to prevent a potential data inconsistency issue which makes ZooKeeper unable to start when no snapshot files present. It's a completely valid scenario in 3.4, so we have an open Jira to fix it: ZOOKEEPER-3056 - Edit: It is done and from 3.5.6 this issue will no longer occur.
Solution: The following workaround has been posted on the Jira and is known to be working:
To perform an upgrade (3.4 -> 3.5.5):
- download the "snapshot.0" file attached (ZOOKEEPER-3056)
- copy it to the versioned directory (e.g. "version-2") within your data directory (parameter "dataDir" in your config - this is the directory containing the "myid" file for a peer)
- restart the peer
- upgrade the peer (this can be combined with the above step if you like)
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