If you are going to build what you are talking about, you are going to have
to have 4 collector entities, and a writer entity, and do clean up.
<<<<>>>>> Player Updates data Base <<><><><><>
Get Player Number,
Select bucket to write to, (any of the following)
Collector Player 1: Turn 1 OBJECT
Collector Player 2: Turn 1 OBJECT
Collector Player 3: Turn 1 OBJECT
Collector Player 4: Turn 1 OBJECT
If (all players checked in = True ) {
Create Turndata
Write to BlobStore }
Return URL of the Blob store, (even if doesn't yet exist)
<><><><><><><><>< Send Players new data <><><><><><>
If ( exists Blob store ){
Return BlobStore
}
Else {return 302 to this url}
<><><><><><><>
This is going to be expensive to run.
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Jeff Schnitzer
Sent: Thursday, May 26, 2011 1:18 PM
To: [email protected]
Subject: Re: [google-appengine] Memcache proper use?
This is unlikely to work.
You will need to transactionally update each game session entity every
0.5 second. You might get that kind of throughput, but with collisions you
may not. The docs officially say don't expect more than 1 write per second
per entity group.
Memcache can flush at any moment, so you cannot use it as an authoritative
source of game state. You can't use it as a cache of game state either
because there is no way to transactionally link it to the datastore - and
you will have major contention issues.
If you want a game architecture like this, you should use a Backend that
periodically checkpoints its state to the datastore.
Honestly, you'll have a lot easier time building your system on a different
platform with MongoDB (or one of the other high-throughput datastores).
Jeff
On Thu, May 26, 2011 at 1:08 PM, Rohan Chandiramani <[email protected]>
wrote:
> Alright, let's give a concrete example.
> I'm still working on my game application.
> Each gamesession holds 4 players and each player updates the shared
> gamession entity once every 2 sec.
> Basically every time a player requests the gamesession entity, he/she
> needs the most up2date entity.
> I don't quite understand what you mean with the durability of writes,
> as English is not my primary language.
>
> Do you mean with durability the amount of time the entity lives in the
> memcache?
> In that case: the entity should stay alive for no less then 6 minutes,
> after
> 6 minutes it'l be deleted from the datastore anyway.
>
> If you meant durability as in the likely hood of the request failing
> to update in memcache?
> That would be catastrophic i guess(however a few lines of could should
> change that).
> Now in the case of delaying writes to the datastore(with a Task Queue
> i
> presume?)
> A risk would be that:
>
> Player0 sends an update.
> Memcache is updated.
> Task is made.
> Memcache entity bites the dust.
> Player1 asks for an update.
> Memcache picks up the entity in the datastore, wich hasn't been
> adjusted yet from the task.
> Player1 gets an old update, and there is an temporary desync in the
client.
> Now that would be an unwanted but tolerable situation.
> I guess it all comes down to, how long my entity will live in memcache.
> And as i've read the docs, memcache is unreliable.
> Yet is this unreliability after some amount of time or could an entity
> get lost after 0:05 seconds of creation(so to speak).
> Maybe even more important, what kind of error margin would i be looking
at.
> After reading this, could you conclude anything about whether to use
> memcache in my case?
> I'm guessing delaying writes would not be a smart option in my case?
>
> I hope my story is understandable.
> Much appreciated,
> Rohan
>
>
>
>
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