suggestion: do not require masterUrl for config

[Jonathan Rochkind <ro...@jhu.edu>]

Suggestion, curious what other people think of it, if I should bother 
filing a JIRA and/or trying to come up with a patch.

Currently, when you configure a replication <lst name="slave">, you HAVE 
to give it a <masterUrl>.

SEVERE: org.apache.solr.common.SolrException: 'masterUrl' is required 
for a slave
         at org.apache.solr.handler.SnapPuller.<init>(SnapPuller.java:126)
         at 
org.apache.solr.handler.ReplicationHandler.inform(ReplicationHandler.java:775)
         at 
org.apache.solr.core.SolrResourceLoader.inform(SolrResourceLoader.java:508)
         at org.apache.solr.core.SolrCore.<init>(SolrCore.java:588)


At first this makes sense, why would you want a slave without a 
masterUrl?  But since you can supply the masterUrl as a query parameter 
in /replication?command=fetchIndex&masterUrl=X, there's really no reason 
to require you to specify it in the solrconfig.xml, if you are planning 
on not having automatic polling, but just triggering replication 
manually, and supplying the masterUrl in the command every time.   This 
can sometimes be convenient for letting some other monitor process 
decide when and how to replicate, instead of having solr itself be 
configured for pulling via polling.

Does that make any sense?