For index updates, Solr relies on fast bulk reads and writes. One way to satisfy these requirements is to ensure that a large disk cache is available. Use local indexes and the fastest disks possible. In a nutshell, you want to have enough memory available in the OS disk cache so that the important parts of your index, or ideally your entire index, will fit into the cache. Let’s say that you have a Solr index size of 8GB. If your OS, Solr’s Java heap, and all other running programs require 4GB of memory, then an ideal memory size for that server is at least 12GB. You might be able to make it work with 8GB total memory (leaving 4GB for disk cache), but that also might NOT be enough