When working with NoSQL solutions such as Solr, we usually don't have the notion of transaction and we can't predict the sequence in which documents will be received by Solr and indexed especially when indexing is done from multiple threads and machines. However, in certain cases, such a functionality is needed at least to some degree. For example, we don't want to run an update on a document that was updated between the time period we read the document and sent the update. This recipe will show you how to avoid such situations.