Thanks for getting back to me so quickly!
RE: Your last email, you wrote:
"B can have a value, but A would be unset."
That wouldnt be a problem since i only want the implication A=>B ("If A
exists then B exists").
But I assume you meant:
A can have a value, but B would be unset. Right?
Can you (*really roughly*) say how many memcache instances you are running?
Let's say I would create 1000 "A"s, would I hit all memcaches (with a high
probabilty)? Then the assumption "if all A's exist, then B exists' would
hold...
Or can I influence the hash somehow to end up in the same instance
(something else then finding hash collisions :)) ?
Thanks again, for getting back to me so quickly.
-Andrin
On Fri, Jul 22, 2011 at 7:55 PM, Ikai Lan (Google) <ika...@google.com>wrote:
> One more thing to be aware of: there are times when Memcache needs to be
> flushed. If a flush happens sometime, B can have a value, but A would be
> unset.
>
> Ikai Lan
> Developer Programs Engineer, Google App Engine
> Blog: http://googleappengine.blogspot.com
> Twitter: http://twitter.com/app_engine
> Reddit: http://www.reddit.com/r/appengine
>
>
>
> On Fri, Jul 22, 2011 at 1:53 PM, Ikai Lan (Google) <ika...@google.com>wrote:
>
>> Oh, I see what you're getting at: you're asking me if B will still be in
>> the cache if A is still in the cache. That depends on whether or not the
>> keys hash to the same Memcache instance.
>>
>> FYI - in general, we don't make any guarantees of this behavior, so it
>> potentially can be problematic down the line if this changes.
>>
>>
>> Ikai Lan
>> Developer Programs Engineer, Google App Engine
>> Blog: http://googleappengine.blogspot.com
>> Twitter: http://twitter.com/app_engine
>> Reddit: http://www.reddit.com/r/appengine
>>
>>
>>
>> On Fri, Jul 22, 2011 at 1:52 PM, Ikai Lan (Google) <ika...@google.com>wrote:
>>
>>> Memcache works like an LRU cache, but I don't see why a would force out b
>>> unless you ran out of space.
>>>
>>> Also, App Engine's Memcache has 2 LRU structures: an app specific LRU and
>>> a global LRU for that Memcache instance.
>>>
>>> Ikai Lan
>>> Developer Programs Engineer, Google App Engine
>>> Blog: http://googleappengine.blogspot.com
>>> Twitter: http://twitter.com/app_engine
>>> Reddit: http://www.reddit.com/r/appengine
>>>
>>>
>>>
>>> On Fri, Jul 22, 2011 at 1:05 PM, Andrin von Rechenberg <
>>> andri...@gmail.com> wrote:
>>>
>>>> Hey there
>>>>
>>>> I'm building something like "Google Analytics" for Appengine but in real
>>>> time
>>>> (Including qps, hourly & daily graphs, backend counters, monitors with
>>>> alerts, etc...)
>>>> The cool thing is that it only uses memcache to increase counters/stats
>>>> so its
>>>> really quick to use in prod code. Every minute I gather all counters and
>>>> write them to datastore.
>>>> It seems to work perfectly for my app (~250qps with about 1000 different
>>>> counters, and about
>>>> 1000 counter increases per second)
>>>> I can also measure how correct my data is (if stuff flushed in memcache,
>>>> but so far that never happened),
>>>> but it's all based on one assumption:
>>>>
>>>> If I call:
>>>>
>>>> memcache.incr("a", intitail_value=0)
>>>> ...
>>>> memcache.incr("b", initial_value=0)
>>>> ....
>>>> memcache.incr("b", initial_value=0)
>>>> ....
>>>>
>>>> *if "a" is still in the memcache "b" will also be in the memcache and
>>>> wont have been flushed, correct?*
>>>> *
>>>> *
>>>> or in other words: If the entity size for two items in the memcache is
>>>> the same,
>>>> does the memcache work like either a LRU or FIFO cache?
>>>>
>>>> Any response is greatly appreciated...
>>>>
>>>> -Andrin
>>>>
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>>>
>>>
>>
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