AFCache class - which objects and collections are cached?

Discussion created by MikeRay on Mar 6, 2013
Latest reply on Mar 8, 2013 by cmanhard

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Hi All,

I am trying to optimize performance of my application and to this end I am looking at setting sensible CacheTime and MaxObjects values. As part of this I need to know what types of objects are kept in the cache. The documentation says this:

"This class caches certain AF objects and collections to prevent them from untimely garbage collection. " and "The AF SDK will cache certain objects and collections for a short period of time to prevent them from being garbage collected too soon. You can use the properties and methods of this class to control how long and how many objects the AF SDK will cache. You can also request that the AF SDK empties its cache. "

Does anyone know or can explain what the certain objects and collections are?

Thanks for the assistance.

Mike.

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RJKSolutions Mar 6, 2013 1:32 PM

My take is that essentially any of the static methods with the verb "Load" or "Find" on an object will cache the object for 120 seconds (by default) so they are not taken by GC. For example, on an AFElement if you "LoadParents" then those objects get cached, but if you "GetParents" those do not.

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MikeRay @ RJKSolutions on Mar 7, 2013 3:54 AM

Thanks Rhys, can anyone from OSIsoft elaborate more on this please? Are whole load / find result collections cached?

Thanks,

Mike.

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cmanhard

@ MikeRay on Mar 8, 2013 1:49 AM

Rhys summed it up pretty well. The cache is used to hold onto all "transactable objects - things you check-in/out". Its purpose is to delay their garbage collection so that the AF SDK isn't continually reloading objects from the server. So, yes, whole load/find result collections are added to the cache. Implicit loads of collections: (Database.ElementTemplates, Element.Elements, etc) are also cached. Non-transactiable collections (Element.Attributes, Element.Categories) are not put in the cache directly - they are held as long as the owning transactable objects are not GC'd.

It is possible to turn caching completely off, or reduce it and write your own. For example, the AFExport utilitly significantly reduces the cache because it doesn't revisit most objects more than once. The export utiliity holds things that it knows will reused in memory (templates, categories, reference types).

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MikeRay @ cmanhard on Mar 8, 2013 9:09 AM

Thanks Chris, this gives me a better understanding. We are indeed trying to decide if we need to make our own caching mechanism in our application. Just one final thing to confirm, a cache is held on the client per user connected to the server, is this correct?

Cheers,

Mike.

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cmanhard

@ MikeRay on Mar 8, 2013 1:40 PM

Trick question. AFCache itself is only used to prevent GC of objects. While the AFCache itself is shared amongst all users, objects inside are never shared between users.

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5 Replies

RJKSolutions Mar 6, 2013 1:32 PM
My take is that essentially any of the static methods with the verb "Load" or "Find" on an object will cache the object for 120 seconds (by default) so they are not taken by GC. For example, on an AFElement if you "LoadParents" then those objects get cached, but if you "GetParents" those do not.
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- MikeRay @ RJKSolutions on Mar 7, 2013 3:54 AM
  Thanks Rhys, can anyone from OSIsoft elaborate more on this please? Are whole load / find result collections cached?
  
  Thanks,
  
  Mike.
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  - cmanhard @ MikeRay on Mar 8, 2013 1:49 AM
    Rhys summed it up pretty well. The cache is used to hold onto all "transactable objects - things you check-in/out". Its purpose is to delay their garbage collection so that the AF SDK isn't continually reloading objects from the server. So, yes, whole load/find result collections are added to the cache. Implicit loads of collections: (Database.ElementTemplates, Element.Elements, etc) are also cached. Non-transactiable collections (Element.Attributes, Element.Categories) are not put in the cache directly - they are held as long as the owning transactable objects are not GC'd.
    
    It is possible to turn caching completely off, or reduce it and write your own. For example, the AFExport utilitly significantly reduces the cache because it doesn't revisit most objects more than once. The export utiliity holds things that it knows will reused in memory (templates, categories, reference types).
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    - MikeRay @ cmanhard on Mar 8, 2013 9:09 AM
      Thanks Chris, this gives me a better understanding. We are indeed trying to decide if we need to make our own caching mechanism in our application. Just one final thing to confirm, a cache is held on the client per user connected to the server, is this correct?
      
      Cheers,
      
      Mike.
      
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      - cmanhard @ MikeRay on Mar 8, 2013 1:40 PM
        Trick question. AFCache itself is only used to prevent GC of objects. While the AFCache itself is shared amongst all users, objects inside are never shared between users.
        
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AFCache class - which objects and collections are cached?

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