This page lists frequently asked questions and answers about ZooKeeper upgrading.
Upgrade to 3.5.5
Supported upgrade path: upgrading to 3.5.5 is only supported from a stable 3.4 version.
To get the best results it's strongly advised to upgrade to the latest stable 3.4 version before upgrading you ensemble to 3.5.5.
Error message: "java.io.IOException: No snapshot found, but there are log entries. Something is broken!"
This is a known issue in upgrading from 3.4 to 3.5. 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
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