FYI real-time get handler is needed for Solr cloud recovery.

[Daniel Collins <da...@gmail.com>]

Just had an issue on our Solr cloud and wanted to point this out to the
list at large.

The real-time "/get" handler is used by Solr Cloud's sync/recovery
mechanism, so *DO NOT* remove it from SolrConfig if you are using Solr
Cloud!

We did (because we weren't using real-time get ourselves and we were trying
to remove all the unnecessary stuff from solrconfig).  What it means is
that whenever a leadership change for a shard happens, ALL the replicas go
into full recovery mode, since they can't determine whether they are in
sync or not.

There seem to get some "getVersions" messages which are implemented in the
RealTimeGetComponent, and since these are required for cloud recovery,
shouldn't there be more emphasis on this being a required component (or
part of the Core Admin Handler so it can't be configured away?)

We have the comments in schema that the _version field is mandatory for
SolrCloud, I think we at least need something similar for the "/get"
handler.

I'll log a JIRA for this, but sending here first.