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* Adaptive caching impl * Adaptive caching tests * Better nullability * Add prop IFusionCache.HasDistributedCache * Added a warning log for the special case of memory cache + backplane + DefaultEntryOptions.EnableBackplaneNotifications == true but without a distributed cache * Perf boost: use factory soft timeout as lock timeout when acquiring the lock if fail-safe is enabled + there is no specific lock timeout + there is a fallback entry * Docs: adaptive caching * Better stale hit for old stale data
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| <div align="center"> | ||
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| # 🧙♂️ Adaptive Caching | ||
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| Sometimes when you are caching a piece of data with the `GetOrSet` method you don't know upfront what the cache duration should be: this may happen because the cache duration depends on the object being cached itself. | ||
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| Some examples may be: | ||
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| - **📰 news articles**: a fresh article that has just been published on a news site may very well receive some updates very soon, maybe because it has been published very fast to get a news out but then some typos have been found or a slight change is needed. In this case it would be nice to be able to cache fresh content for a low amount of time like `30 sec` or `1 min`, whereas an old article that has not been touched for a year may very well be cached for like `10 min` or more, because it will be very unlikely that a quick update will be needed after all this time | ||
| - **🔑 auth tokens**: auth tokens or similar pieces of data typically have an associated expiration, and it would be nice to cache them accordingly | ||
| - **🌍 HTTP api results**: if your remote data source is not a database but, for example, an HTTP service like a rest endpoint the HTTP response may contain caching-related informations in the form of the `Cache-Control` HTTP header, which in turns typically contains the `max-age` directive. It would be nice to use that as the duration for the cache, respecting the service specification for how much a piece of data should be cached | ||
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| The problem in all these cases is that when you call `GetOrSet` you'll provide both the factory (the function to be executed to get the data) and some options for that call (via `FusionCacheEntryOptions`), but as we said some of the options (eg: the `Duration`) may depend on the result of the factory, which has not run yet. | ||
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| It seems like a chicken and egg problem, right? | ||
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| Thankfully we have a solution: enter **adaptive caching**. | ||
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| ## 👩🏫 How it works | ||
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| When calling `GetOrSet` you can choose different overloads, and the ones with a factory are available in 2 factory flavors: one with a *context* (of type `FusionCacheFactoryExecutionContext`) and one without it. | ||
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| In the ones **with** the context you can simply change the context's `Options` property however you like. | ||
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| Here are 2 examples, with and without the *context* object. | ||
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| ### Example: without adaptive caching | ||
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| As you can see we are specifying the factory as a lambda that takes as input only a cancellation token `ct` (of type `CancellationToken`) and nothing else. | ||
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| ```csharp | ||
| var id = 42; | ||
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| // WITHOUT ADAPTIVE CACHING: THE DURATION IS FIXED TO 1 MIN | ||
| var product = cache.GetOrSet<Product>( | ||
| $"product:{id}", | ||
| ct => GetProductFromDb(id, ct), | ||
| options => options.SetDuration(TimeSpan.FromMinutes(1)) // FIXED: 1 MIN | ||
| ); | ||
| ``` | ||
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| ### Example: with adaptive caching | ||
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| As you can see we are specifying the factory as a lambda that takes as input both a context `ctx` (of type `FusionCacheFactoryExecutionContext`) and a cancellation token `ct` (of type `CancellationToken`), so that we are able to change the options inside the factory itself. | ||
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| ```csharp | ||
| var id = 42; | ||
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| // WITH ADAPTIVE CACHING: THE DURATION DEPENDS ON THE OBJECT BEING CACHED | ||
| var product = cache.GetOrSet<Product>( | ||
| $"product:{id}", | ||
| (ctx, ct) => { | ||
| var product = GetProductFromDb(id, ct); | ||
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| if (product is null) { | ||
| // CACHE null FOR 5 minutes | ||
| ctx.Options.Duration = TimeSpan.FromMinutes(5); | ||
| } else if (product.LastUpdatedAt > DateTime.UtcNow.AddDays(-1)) { | ||
| // CACHE PRODUCTS UPDATED IN THE LAST DAY FOR 1 MIN | ||
| ctx.Options.Duration = TimeSpan.FromMinutes(1); | ||
| } else if (product.LastUpdatedAt > DateTime.UtcNow.AddDays(-10)) { | ||
| // CACHE PRODUCTS UPDATED IN THE LAST 10 DAYS FOR 10 MIN | ||
| ctx.Options.Duration = TimeSpan.FromMinutes(10); | ||
| } else { | ||
| // CACHE ANY OLDER PRODUCT FOR 30 MIN | ||
| ctx.Options.Duration = TimeSpan.FromMinutes(30); | ||
| } | ||
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| return product; | ||
| }, | ||
| options => options.SetDuration(TimeSpan.FromMinutes(1)) // DEFAULT: 1 MIN | ||
| ); | ||
| ``` | ||
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| You may change other options too, like the `Priority` for example. | ||
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| Of course ther are some changes that wouldn't make much sense: if for example we change the `FactorySoftTimeout` after the factory has been already executed we shouldn't expect much to happen, right 😅 ? | ||
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| ## ⏱ Timeouts & Background factory completion | ||
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| Short version: everything works as expected! | ||
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| Longer version: there are times when, if a factory is taking a lot of time to complete (because maybe the database is overloaded or there's a temporary network congestion), you would prefer stale data very fast instead of fresh data but slowly. | ||
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| A nice feature of FusionCache is the ability to set soft/hard [timeouts](Timeouts.md) to get the best of both worlds: an always fast response with fresh data as soon as possible. As we know when a timeout kicks in, the running factory is not stopped but kept running in the background. | ||
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| A question we may ask ourselves is if adaptive caching would still work in that scenario. | ||
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| The answer is **absolutely yes**: you don't need to change anything, do extra steps or give up on some features 🎉 |
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