I wonder whether this is a known bug. In previous SOLR cloud versions, 4.4 or maybe 4.5, an explicit optimize(), without any parameters, it usually took 2 minutes for a 32 core cluster.
However, in 4.6.1, the same call took about 1 hour. Checking the index modification time for each core shows 2 minutes gap if sorted. We are using a solrj client connecting to zookeeper. I found it is talking to a specific solr server A, and that server A is distributing the calls to all other solr servers. Here is the thread dump for this server A: at org.apache.solr.client.solrj.impl.HttpSolrServer.request(HttpSolrServer.java:395) at org.apache.solr.client.solrj.impl.HttpSolrServer.request(HttpSolrServer.java:199) at org.apache.solr.client.solrj.impl.ConcurrentUpdateSolrServer.request(ConcurrentUpdateSolrServer.java:293) at org.apache.solr.update.SolrCmdDistributor.submit(SolrCmdDistributor.java:226) at org.apache.solr.update.SolrCmdDistributor.distribCommit(SolrCmdDistributor.java:195) at org.apache.solr.update.processor.DistributedUpdateProcessor.processCommit(DistributedUpdateProcessor.java:1250) at org.apache.solr.handler.RequestHandlerUtils.handleCommit(RequestHandlerUtils.java:69)
