...
Other possible problems that cause slow indexing include committing after every update request, sending one document at a time in each update request instead of batching them, and only using one thread/connection to index. These are problems that are external to Solr. Possible workaround is using the IgnoreCommitOptimizeUpdateProcessorFactory to ignore all commits from client and instead setup autoCommit.
One part of that needs emphasis. Using only one thread or process for indexing is very often the cause of slow indexing. Using multiple threads or processes to do indexing in parallel will be faster than a single thread. For best results, both the indexing system and the system(s) running Solr should have as many CPU cores as you can get.
Further help
If you need additional help with any of the issues discussed on this page, Solr has a very active community. Be sure that you can provide relevant information before asking for help.