I'm pretty sure we found the problem. It's related to memory. Sometimes Windows seems to unmap index files from memory, because other processes need it. To force Windows to map index files again, we need to rebuild the index. We can clearly see this behaviour with tools like RAMMap.
With servers 100% dedicated to Solr (no other softwares on the server), this problem does not occur. -- Sent from: https://lucene.472066.n3.nabble.com/Solr-User-f472068.html
