On 3/14/2018 3:04 AM, Hendrik Haddorp wrote:
we have a SolrCloud 6.3 with HDFS setup and plan to upgrade to 7.2.1.
The cluster upgrade instructions on
https://lucene.apache.org/solr/guide/7_2/upgrading-a-solr-cluster.html
does not contain any information on changing the luceneMatchVersion.
If we change the luceneMatchVersion manually is it enough to just
reload the collection or do we need to perform an index upgrade like
the IndexUpgrader tool
(https://lucene.apache.org/solr/guide/7_2/indexupgrader-tool.html)
does? If so how would one use that for an index stored in HDFS?
Most people seem to expect that defining luceneMatchVersion will allow
them to build an index with the format of an earlier version.
This is not what happens. Solr builds indexes in the format that the
same version of Lucene chooses by default. As far s I know, you can't
change the index format in Solr.
Somebody who is writing a Lucene program (instead of using Solr) can
choose to use an earlier version's format, but this is not done with
luceneMatchVersion.
The luceneMatchVersion setting is used by the index analysis components
(tokenizers, filters, etc). Sometimes when a component's behavior is
SIGNIFICANTLY changed by a version upgrade, the developer will put in a
luceneMatchVersion check so users can revert to the old behavior if they
want to. Only a minority of changes to analysis components are
controlled by luceneMatchVersion.
Generally there is no need to use the IndexUpgrader tool unless you're
updating at least two major version numbers. This is because a 7.x
version can only read version 6.x indexes. Anything earlier must be
upgraded to 6.x.
But it's my strong opinion that if you're upgrading two major versions,
then you should build a new index from scratch, and use a new
configuration that has been designed from the ground up for the new
version. Users who upgrade that far often find that they cannot use
their configurations in the new version without changes, so they MUST
rebuild.
I actually recommend always building the index from scratch for ANY Solr
upgrade.
Thanks,
Shawn
