My apologies; I've just found the answer (that optimisation should be on the master server only)
________________________________ From: Matthew Painter Sent: Sunday, 11 October 2009 12:34 p.m. To: 'solr-user@lucene.apache.org' Subject: Optimize on slaves? Hi, Simple question! I have a nightly cron job to send the optimize command to Solr on our master instance. Is this also required on Solr replicated slaves to optimise their indexes? Thanks, Matt This e-mail message and any attachments are CONFIDENTIAL to the addressee(s) and may also be LEGALLY PRIVILEGED. If you are not the intended addressee, please do not use, disclose, copy or distribute the message or the information it contains. Instead, please notify me as soon as possible and delete the e-mail, including any attachments. Thank you.