In simple words, when you make a request in Jackett, the results are saved in memory (cache). The next request will return results form the cache improving response time and making fewer requests to the sites.
* We assume all indexers/sites are stateless, the same request return the same response. If you change the search term, categories or something in the query Jackett has to make a live request to the indexer.
* There are some situations when we don't want to use the cache:
** When we are testing the indexers => if query.IsTest results are not cached
** When the user updates the configuration of one indexer => We call CleanIndexerCache to remove cached results before testing the configuration
** When there is some error/exception in the indexer => The results are not cached so we can retry in the next request
* We want to limit the memory usage, so we try to remove elements from cache ASAP:
** Each indexer can have a maximum number of results in memory. If the limit is exceeded we remove old results
** Cached results expire after some time
* Users can configure the cache or even disable it
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