Closing a core will shutdown almost everything related to the workings of a core. Update and search handlers, possible warming searchers etc.
Check the implementation of the close method: http://svn.apache.org/viewvc/lucene/dev/branches/branch_3x/solr/src/java/org/apache/solr/core/SolrCore.java?view=markup > 2011-02-16 11:32:45.489::INFO: Shutdown hook executing > 2011-02-16 11:35:36.002::INFO: Shutdown hook complete > > The shutdown time seems to be proportional to the amount of time that Solr > has been running. If I immediately restart and shut down again, it takes > a fraction of a second. What causes it to take so long to shut down and > is there anything I can do to make it happen quicker?