On Wednesday, 30 April 2014 02:58:34 UTC+10, Jeremy Evans wrote:
>
> On Monday, April 28, 2014 8:34:46 PM UTC-7, russ m wrote:
>>
>>
>> My use case is a database that is caching resources from a crappy REST
>> source that only supports "get resource by ID" and "get all resources
>> modified since this timestamp" operations. At the moment the cache is
>> updated on a schedule (so is always a little stale, and is read-only to our
>> application), and I'd like to try out refreshing the cache on every
>> retrieval of a Sequel::Model object.
>>
>
> If you are refreshing the cache on every retrieval, then you probably
> should not be caching at all.
>
>>
Not a full refresh, but a "get resources modified since" the most recent
last-modified time on each table - in practice this will usually return no
or very few (ie <10) changed records.
Also, the local cache isn't there for speed but to be able to make useful
queries against the published data, since the provided API is so thin.
> As far as I can tell I can't use the Sequel::Model#initialize like the
> AfterInitialize
>> plugin does, since model objects aren't instantiated unless the dataset
>> query returns rows.
>>
>> Before I wade into datasets to see where/how to hook them, can anybody
>> point me at a good spot to look at doing this?
>>
>
> The only place I can think of to do this is to override Dataset#each for
> the model's dataset:
>
> ModelClass.dataset_module{def each; refresh_cache; super end}
>
Thanks, I'll check that out.
> But that may refresh the cache more often than you want. A better
> approach if this is a web application is to add a before hook or rack
> middleware that will reload the cache before the appropriate actions. That
> way you are only refreshing once per web request.
>
Throttling cache refreshes is the obvious first optimisation, but I was
going to leave that until after I had a working implementation.
cheers
R.
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