we see at least two problems when scaling to large number of collections. I would like to ask the community, if they are known and maybe already addressed in development: We have a SolrCloud running with the following numbers: - 5 Servers (each 24 CPUs, 128 RAM) - 13.000 Collection with 25.000 SolrCores in the Cloud The Cloud is working fine, but we see two problems, if we like to scale further 1. Resource consumption of native system threads We see that each collection opens at least two threads: one for the zookeeper (coreZkRegister-1-thread-5154) and one for the searcher (searcherExecutor-28357-thread-1) We will run in "OutOfMemoryError: unable to create new native thread". Maybe the architecture could be changed here to use thread pools? 2. The shutdown and the startup of one server in the SolrCloud takes 2 hours. So a rolling start is about 10h. For me the problem seems to be that leader election is "linear". The Overseer does core per core. The organisation of the cloud is not done parallel or distributed. Is this already addressed by https://issues.apache.org/jira/browse/SOLR-5473 or is there more needed?
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