[jira] [Created] (SOLR-9915) PeerSync alreadyInSync check is not backwards compatible

["Tim Owen (JIRA)" <ji...@apache.org>]

Tim Owen created SOLR-9915:
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             Summary: PeerSync alreadyInSync check is not backwards compatible
                 Key: SOLR-9915
                 URL: https://issues.apache.org/jira/browse/SOLR-9915
             Project: Solr
          Issue Type: Bug
      Security Level: Public (Default Security Level. Issues are Public)
          Components: replication (java)
    Affects Versions: 6.3
            Reporter: Tim Owen


The fingerprint check added to PeerSync in SOLR-9446 works fine when all servers are running 6.3 but this means it's hard to do a rolling upgrade from e.g. 6.2.1 to 6.3 because the 6.3 server sends a request to a 6.2.1 server to get a fingerprint and then gets a NPE because the older server doesn't return the expected field in its response.

This leads to the PeerSync completely failing, and results in a full index replication from scratch, copying all index files over the network. We noticed this happening when we tried to do a rolling upgrade on one of our 6.2.1 clusters to 6.3. Unfortunately this amount of replication was hammering our disks and network, so we had to do a full shutdown, upgrade all to 6.3 and restart, which was not ideal for a production cluster.

The attached patch should behave more gracefully in this situation, as it will typically return false for alreadyInSync() and then carry on doing the normal re-sync based on versions.



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