SOLR Statistics was introduced with DSpace =>1.6.2. SOLR statistics are now enabled by default for the XMLUI in DSpace versions =>3.2.
Step 1 - Optimise statistics database
Before upgrading DSpace, run SOLR statistics optimisation $HOME/bin/dspace stats-util -o at least once just before the upgrade!
Step 2 - Backup statistics database
If you are upgrading, you need to backup the SOLR database before doing any new configuration.
Type the following to backup the SOLR DB: (If using Ubuntu 12.04 LTS, replace tomcat7 with tomcat6)
sudo service tomcat7 stop
cp -Rv $HOME/solr/ $HOME/backup/
sudo service tomcat7 start
Step 3 - Adding new SOLR statistics database fields
New statistics fields were introduced in DSpace 4.X, therefore any upgrade from a DSpace version <= 3.X will not have these fields.
The lack of these new fields in statistics records from previous versions of DSpace, causes major errors when attempting to do statistics maintenance in DSpace versions => 4.X after an upgrade from a lower version of DSpace. See the link below for a possible fix.
Because of this problem, we are considering using Elastic Statistics exclusively instead, which seems to be more stable and provides download data not just visits and views.
The issue is being discussed on this wiki page: https://wiki.duraspace.org/display/DSPACE/DSpace+statistics+-+current+status+and+future+development
Also see the following about work to automatically fix old statistics databases.