Re: [Hibernate] JCS cache - Distributable read-write

[Christian M. <vc...@cl...>]

Thanks Gavin for this !

At this stage of my brainstorming about the cache, if i had to code it, =
the logic would be this:

The Cache interface should be like yours but with a remove method also.

CachedItem would be simplified to :

{
    private long timestamp;
    private Object value
}

ClassPersister would hold a JCSCache instance


Load operation:

The method responsible for loading an object in the session would do the =
following ( very simplified view of the code, just the logic here)

if( cache.get(...) !=3D null) // the item is already in a cache and we =
get it from there
{
        if(CachedItem.getTimestamp() < session.getTimestamp() ) // has =
this cacheditem been put in the cache before the session has begun ?
        {
                //Use the cacheditem to assemble the object
        }
        else
        {
                LoadFromDb()  // load the item from the databaase
                                      // Notice that we do not then put =
the loaded item in the cache       =20
        }
}
else
{
        LoadFromDb()      // Load the item from the database
        cache.put(item)    // put the item in the cache
}

Update/Delete operation:

--> The session hold a set of the items that have been updated/deleted =
in the transaction, when the transaction commit, we iterate the set and =
remove each entry from the cache.

With this logic, we end with a read only cache ( we never update an item =
in the cache) for mutable objects.

Do you see an example where the transaction isolation would fail with =
this logic ?
Do you see why this would not work using a lateral caching in JCS ?

Regards
Christian Meunier

  ----- Original Message -----=20
  From: Gavin King=20
  Cc: hibernate list=20
  Sent: Thursday, September 19, 2002 1:34 PM
  Subject: Re: [Hibernate] JCS cache - Distributable read-write


  This is the email:

  =
http://sourceforge.net/mailarchive/forum.php?thread_id=3D1033840&forum_id=
=3D7517
    ----- Original Message -----=20
    From: Gavin King=20
    To: Christian Meunier=20
    Cc: hibernate list=20
    Sent: Thursday, September 19, 2002 9:25 PM
    Subject: Re: [Hibernate] JCS cache - Distributable read-write


    Nice diagram! I wish the Hibernate doco had some diagrams like =
that....

    What I mean by "transactional access" is we would have to be able to =
read a value out of the cache, check its timestamp, and then put a new =
value in the cache as an atomic operation. Currently we do this by =
synchronizing on the strategy object. That approach won't work for a =
distributed cache. I detailed an approach that would work (a remote =
LockServer) in a previous email. If you read that carefully you will see =
exactly how isolation would be broken without it.