jodydonetti
commented
2 years ago Hello @darcome and thanks for trying out FusionCache!
FusionCache does not support traditional sliding expiration itself, but that is by design because you can get the same results (or even more!) with a different approach.
In my experience a "simple" sliding expiration may lead to situations where you end up having a cache entry that is used a lot and, because of that, it keeps "sliding" and never expires, and so it never update itself. This of course unless there's a separate update call somewhere, but sometimes it's easy to forget to do that in some situations or to miss one call.
Usually the reason sliding expiration is used is because we want to keep something in the cache until it is used, without having to wait for a (maybe) slow call to populate it, but as I said this may lead to missed updates along the line.
Instead you can obtain an even better result in a different way: just enable both fail-safe and set some timeouts.
Let's see a practical example.
Say we want to:
- cache something for
5 min - if it's used after those
5 min, keep it around and re-use it, but for no more than10 min(to avoid data that is too much stale) - be able to automatically update it, if it's still getting used (like "simple" sliding expiration)
- get the value ideally in no more than
50 ms
To do that you just need to do this (eg: a product from the database):
var product = cache.GetOrSet<Product>(
"product:123",
_ => GetProductFromDb(123),
options => options
// CACHE DURATION
.SetDuration(TimeSpan.FromMinutes(5))
// ENABLE FAIL-SAFE, MAX 10 MIN
.SetFailSafe(true, TimeSpan.FromMinutes(10))
// SET A 50 MS SOFT TIMEOUT
.SetFactoryTimeouts(TimeSpan.FromMilliseconds(50))
);In this way what you get is still a "sliding" duration of 5 min, but including the automatic update of the data itself if needed, all without having to wait for a slow db call (that may happen if the db is temporarily overloaded or if there's a temporary network congestion or whatever) and all while not keeping it in the cache for more than 10 min if nobody uses it (saving memory).
It basically boils down to a sliding duration of 5 min + another 5 min in which it has time to auto-update the data automatically, and everytime there's a fresh piece of data, the 5-10 min duration starts back, like the "simple" sliding expiration itself.
One last thing: to simplify the code even more and save some memory you may want to create an options variable and re-use it, like this:
// SOMEWHERE AT STARTUP
var slidingOptions = new FusionCacheEntryOptions(TimeSpan.FromMinutes(5))
.SetFailSafe(true, TimeSpan.FromMinutes(10))
.SetFactoryTimeouts(TimeSpan.FromMilliseconds(50));
// [...]
// LATER ON
var product = cache.GetOrSet<Product>(
"product:123",
_ => GetProductFromDb(123),
slidingOptions
);I usually put a set of common caching options in a public static class, like a singleton, and always refer to them for better code centralization and easu of use, but that's a personal choice. Something like this:
public static class MyCachingOptions {
public static FusionCacheEntryOptions Products = new FusionCacheEntryOptions(TimeSpan.FromMinutes(5))
.SetFailSafe(true, TimeSpan.FromMinutes(10))
.SetFactoryTimeouts(TimeSpan.FromMilliseconds(50));
public static FusionCacheEntryOptions Users = new FusionCacheEntryOptions(TimeSpan.FromMinutes(1));
public static FusionCacheEntryOptions Categories = new FusionCacheEntryOptions(TimeSpan.FromMinutes(10))
.SetFailSafe(true, TimeSpan.FromHours(1))
.SetFactoryTimeouts(TimeSpan.FromSeconds(10));
// ETC...
}Let me know if you need something else, I hope I've been able to help!
NOTE: the sample is using the sync api to keep it as simple as possible, but everything is also available in an async fashion.
jasenf
darcome
Hello,
I'd like to know if there is the possibility to set a sliding expiration so that if the cached object is updated or read, the expiration counter is restarted.
Is this possible? If not, are there other ways to acheive it?
Thanks in advance and keep up the good work!