Commit 1640587 from Mark Miller in branch 'dev/branches/branch_5x'
[ https://svn.apache.org/r1640587 ]

SOLR-6747: Add an optional caching option as a workaround for SOLR-6586.

Commit 1640582 from Mark Miller in branch 'dev/trunk'
[ https://svn.apache.org/r1640582 ]

SOLR-6747: Add an optional caching option as a workaround for SOLR-6586.

In the short term, I don't see a clean way to deal with this due to a mismatch with the API's. To allow a workaround, I've filed SOLR-6747.

When using JmxMonitoredMap in a pattern of:

JmxMonitoredMap#getMBeanInfo // to get the attributes
JmxMonitoredMap#getAttribute
JmxMonitoredMap#getAttribute
...

Each call of getAttribute calls getStatistics on the SolrInfoMBean.

If there is any expense to the getStatistics call, this can be fairly painful. For example, the ReplicationHandler is registered so that it's getStatistics neeeds to be called twice if you go through all of the SolrInfoMBeans. However, because it's called for each attribute, it's actually called 2 * number of atrribs times. Because the replication handler does things like getting the size of the index directory, this is fairly wasteful.

It seems one option around it is to implement getters for each attribute on the ReplicationHandler and other SolrInfoMBeans. That seems quite cumbersome and long term annoying though.