If there could be a way to force the new version to continue writing in the previous format for a while, that would allow switching to writing the new format once all nodes have been upgraded (or more likely when the cluster admin decides so).
Ilan Le mar. 30 juin 2020 à 21:34, David Smiley <dsmi...@apache.org> a écrit : > I was considering the process of a Solr upgrade to a SolrCloud cluster > within a minor version (e.g. 8.3 -> 8.4). > > A concern I have is the implication of new Lucene index formats. Lucene > 8.4 bumped the Codec version because of postings being written differently > to be more SIMD friendly -- > https://issues.apache.org/jira/browse/LUCENE-9027 > Lucene 8.4 will read an index created with Lucene 8.3 -- great; but Lucene > 8.3 obviously can't read an index created with Lucene 8.4. I'm not picking > on this specific JIRA/change; it could be many others. There's another > coming in 8.6. > > We've got some documentation on the upgrade process: > > https://github.com/apache/lucene-solr/blob/master/solr/solr-ref-guide/src/upgrading-a-solr-cluster.adoc > The instructions describe a rolling upgrading of each node one at a time. > Makes sense. However, it's possible for a shard on an already upgraded > node to become leader, have some documents written to it, and then a > replica on a non-upgraded node might end up replicating segments from the > leader. This is possible with all replica types, though I think more > likely with TLOG & PULL. I am not sure if there are any protections for > this (e.g. in replication handler / index fetcher); there should be. I > think that SolrCloud should prevent a replica from becoming a leader if > there exists another replica (for the same shard) that has a lower Solr > version. > > I can think of two work-arounds: > (A) shut down the whole cluster to do the upgrade (forced down time) > (B) initiate read-only status for all collections > https://github.com/apache/lucene-solr/blob/master/solr/solr-ref-guide/src/collection-management.adoc#L258 > and > also be careful not to create new collections during this time. Then do > the rolling upgrade as described in the docs above, and then remove the > read-only status. > > ~ David Smiley > Apache Lucene/Solr Search Developer > http://www.linkedin.com/in/davidwsmiley >
