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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