[Jboss-dev-forums] [Design of JBossCache] - Re: Proposal: Flat 'Heap' for POJOs stored in PojoCache

[<bst...@jb...>]

"ben...@jb..." wrote : 
  | Brian, I have thought about this issue while designing the new mapping scheme. While the scenario that you mentioned can happen, I think it is more unlikely. The reason being that buddy replication requires "sticky session" to operate in cases like http session repl.
  | 
  | If it is http session repl, then every data structure will be stored under a sessionID. In this case, my undertanding is we will gravitate everything under sessionID in one shot during failover, am I correct. Therefore, shared reference between "joe" and "mary" will still work, for example.

Yes, definitely.  That's why this issue was not a big priority for me for 1.4.0 -- the session replication use case works even if this issue isn't resolved.

Re: walking the object graph and gravitating aggressively vs. lazy gravitation, my instinct is that walking the object graph and gravitating aggressively would be more performant.  Otherwise you end up doing a bunch of single node gravitations at random points. I could be wrong though.  For example, gravitation now is a 2 step process:

1) Please give me everything under Fqn x -- return is a list of NodeData objects.
2) Please remove everything you had under Fqn x, as I now own it.  This is a simple call, I just pass "x".

Doing it in 2 steps is important as you avoid removing the data from the old backup node until the new owner acknowledges he's received it.

With a flat heap it becomed more complex:

1) Please walk an object graph starting at x and give me all nodes.
2) Please rewalk that object graph, but now delete all nodes you have.

I guess that's not that different, but it is different.

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