Setting up to index multiple datastores

[Daniel Miller]

One of the many features of the Dovecot IMAP server is Solr support.  
This obviously provides full-text-searching of stored mails - and it 
works great.  But...the focus of the Dovecot team and mailing list is 
Dovecot configuration.  I'm asking for some guidance on how I might 
optimize Solr.

At the moment I have a (I think!) reasonably well-defined schema that 
seems to perform well.  In my particular use case, I have a single 
physical server running Linux with available VirtualBox virtual 
servers.  I am presently running Solr within one of the virtual servers, 
and I'm running SolrCloud even though I only have one core (it just 
seemed to work better).

Now because I have a single collection/core/shard - all the mail users 
and all their mail folders are stored/indexed/searched by this single 
Solr instance.  I'm thinking that I'd like to split the indexing on at 
least a per-user fashion - possibly also on a per-mailbox fashion.  
Dovecot does allow for variable substitution in the Solr URL - so I 
should be able to generate the necessary URL requests on the Dovecot 
side.  What I don't know is:

1.  Is it possible to split the "indexes" (I'm still learning Solr 
vocabulary) without creating separate "cores" (which to me means 
separate Java instances)?
2.  Can these separate "indexes" be created on-demand - or do they need 
to be explictly created prior to use?

--
Daniel