We learnt in the previous section that the ad distribution system needs to be very fast and capable of handling a large number of requests as compared to a website. In addition, the system should be always available, with the least possible downtime (none if possible). The ads have to be relevant so that merchants obtain the desired response. Let us look at a few parameters that will improve Solr's performance by optimally using the inbuilt caching mechanism.

An index searcher, which is used to process and serve search queries, is always associated with a Solr cache. As long as an index searcher is valid, the associated cache also remains valid. When a new index searcher is opened after a commit, the old index searcher keeps on serving requests until the new index searcher is warmed up. Once the new index searcher is ready, it will start serving all the new search requests. The old index searcher will be closed after it has served all the remaining search requests...