[Vm-dev] A trick to speedup #become: (but not becomeForward:)

Chris Muller asqueaker at gmail.com
Sun Jul 31 22:02:38 UTC 2011

I'm not sure how easy it would be to get the physical size of the
objects which weren't retrieved.  As you said, encoding it in the
referencing oid might be the only way - which would require rewriting
of the OidMap and upgrade of legacy repositories.  :(

I understand why it won't work with becomeForward: - because that
would be creating two copies of the object.  But Magma needs to
becomeForward:, rather than become:, its proxies... (pause to remember
for sure why...).  I think because of proxies to Symbol selectors -
you can't become: any object to a Symbol selector or else their
CompiledMethod literals would refer to the Proxy...  So that would be
another hurdle to overcome to succeed with your idea.

Just so you know, I _did_ implement your other workaround idea - where
reified proxies are "saved up" into a OrderedCollection which is then
bulk-becomed only once every 30 seconds.  I didn't know if you saw it
in the last release (Magma 1.2) - it was a great performance
improvement!  Your creative ideas are really helping Magma.


On Sat, Jul 30, 2011 at 8:12 PM, Igor Stasenko <siguctua at gmail.com> wrote:
> An interesting observation:
> if two oops which we need to swap: oop1 and oop2 taking exactly same
> space in memory,
> then all we need to do is to swap their memory contents, instead of
> scanning heap and updating pointers!
> This makes a become operation extremely cheap for such pairs!
> As for objects of different sizes, we could still use slow algorithm.
> But knowing that if two objects with same size will be swapped much
> faster, a developers could adapt their algorithms to exploit this
> feature
> (use fixed-size objects instead of variable-sized ones etc).
> Magma using proxies, which then #becomeForward: to real objects when reified.
> This is very costly operation and main reason why it so slow on
> loading objects from server.
> To speed thing up, a special trick can be used:
>  - each time server sends an object ID (instead of real object) it
> could also send its size in bytes (or even more clever - you can
> encode object size in its ID ;) ).
> Then a client will create a proxy for given object and will try to
> match the size, if its possible. (nobody said that proxy can't be
> variable-sized, right?)
> Then once client requesting to reify given proxy with real object from
> database, VM will just overwrite a proxy's memory contents with real
> object.
> --
> Best regards,
> Igor Stasenko AKA sig.

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