[Twisted-Python] pb.Cacheable doc question

Stephen Waterbury waterbug at pangalactic.us
Sat Oct 9 11:53:39 EDT 2010

On 10/08/2010 03:46 PM, Glyph Lefkowitz wrote:
> On Oct 8, 2010, at 9:25 AM, exarkun at twistedmatrix.com
> <mailto:exarkun at twistedmatrix.com> wrote:
>> On 5 Oct, 08:09 pm, stephen.c.waterbury at nasa.gov
>> <mailto:stephen.c.waterbury at nasa.gov> wrote:
>>> First, the "PB Copyable: Passing Complex Types" doc is
>>> *great* and the examples are excellent -- my compliments to
>>> all who contributed!
>>> My question is about the pb.Cacheable section
>>> (http://twistedmatrix.com/documents/current/core/howto/pb-
>>> copyable.html#auto9)
>>> -- specifically the first sentence: 'Sometimes the object you
>>> want to send to the remote process is big and slow. "big" means
>>> it takes a lot of data (storage, network bandwidth, processing)
>>> to represent its state. "slow" means that state doesn't change
>>> very frequently.'
>>> I would think that the product of its size and its rate of change
>>> is the applicable metric -- i.e.: the bigger the object is *or*
>>> the faster it changes (not the slower), the more applicable
>>> Cacheable is, no?
>> That seems plausible. I wonder if the rate comment is motivated by
>> something else, like the chance of the remote cache being out of date
>> when the remote side wants to use some of its data. This would increase
>> with the rate of change, but I don't know if it really matters. I
>> haven't ever actually used a Cacheable myself, as far as I can recall.
> I think I probably wrote that paragraph, and it was not very well put.
> Big objects which are "fast", i.e. change constantly, are perfectly
> suitable for Cacheables.
> The point I believe I was trying to make there was that if /a
> significant proportion/ of the object's data is changing quickly,
> Cacheable doesn't make much of a difference over just re-Copyable-ing
> the whole object, since the delta updates will be the same size as the
> whole object.

Certainly true.  Again, the documentation and the examples are great,
anyway, so that part is not a big deal, I was just curious.  Thanks,


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