[Twisted-Python] pb.Cacheable doc question
glyph at twistedmatrix.com
Fri Oct 8 15:46:53 EDT 2010
On Oct 8, 2010, at 9:25 AM, exarkun at twistedmatrix.com wrote:
> On 5 Oct, 08:09 pm, 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
>> -- 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 something else, like the chance of the remote cache being out of date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.
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