CODEWITHSUNDEEP
javacachingguava
Andy Dufresne
Andy Dufresne

Reputation: 6190

Guava thread management when pre-loading and refreshing cache entries

We want to use guava cache for caching third party data to have better response times. The cache needs to be pre-loaded by making a sequence of api calls (~ 4000 api calls are to be made). The api response contains the cache key and its value. These api calls need to be made in parallel from multiple threads (i.e. thread pool) to speed up the cache loading. Each cache entry would have an expiry time. This can be set using expireAfterAccess() call. After a cache entry expires, it needs to be refreshed automatically in the background. Also there should be a way (api) through which we can stop this background cache refresh so that we do not keep making api calls endlessly. We will call this api once we stop getting user requests after a configured time interval.

Is it possible to delegate the thread management for cache loading and refresh to guava? i.e. Given the api call, the code to map the json response to java object and cache key-value design, can guava perform the pre-loading and refresh on its own?

Thanks.

Upvotes: 1

Views: 1804

Answers (1)

cruftex
cruftex

Reputation: 5723

Automatic refreshing in Guava can be enabled via CacheBuilder.refreshAfterWrite(). The relevant semantics are described as:

Specifies that active entries are eligible for automatic refresh once a fixed duration has elapsed after the entry's creation, or the most recent replacement of its value. [ ... ] Currently automatic refreshes are performed when the first stale request for an entry occurs.

When overriding the method CacheLoader.reload() you can use a thread pool to load values asynchronously.

The problem with this behavior is that you always have a few reads of stale values, before the new value has been loaded, if it succeeds. An alternative cache implementation, like cache2k starts the refreshing immediately after the duration. The latter approach leads to more recent data, but possibly more needless reads. See some recent discussion about that here: https://github.com/ben-manes/caffeine/issues/261

Upvotes: 1

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