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Qijing,

I don't believe that this is correct. I promised to send a description
to the ML, I'll do that today.

-amrith

On Sun, 2016-05-15 at 01:16 -0700, Qijing Li wrote:
> Hi Vilobh,  
> 
> Here is my thoughts on how Delimiter uses generation-id to guarantee
>  sequencing. Please correct me if I understand it wrong.
> 
> First, the Delimiter need to introduce another model ResourceProvider
> who has two attributes:
> 
>       * resource_id 
>       * generation_id
> 
> The followings are the steps of how to consume a quota:
> 
> Step 1. Check if there is enough available quota 
> 
>     If yes, then get the $generation_id  by querying the model
> ResourceProvider with the given resource_id which is the point in time
> view of resource usage.
> 
>     If no, terminate the process of consuming the quota and return the
> message of “No enough quotas available."
> 
> Step 2. Consume the quota.
> 
>    2.1 Begin transaction
> 
>    2.2 Update the QuotaUsage model: QuotaUsage.in_use =
> QuotaUsage.in_use + amount of quota requested.
> 
>    2.3 Get the $generation_id by querying the ResourceProvider by the
> given resource_id.
> 
>         If the $generation_id is larger than the $generation_id in
> Step 1, then roll back transaction and GOTO step 1.
> 
>            this case means there is someone else has changed the
> QuotaUsage during this process.
> 
>         If the $generation_id is the same as the $generation_id in
> Step 1, then increase the ResourceProvider.generation_id by one and
> 
>         Commit the transaction. Done!
> 
>         Note: no case the $generation_id is less than the
> $generation_id in Step 1 because the $generation_id is nondecreasing.
> 
> 
> — Qijing
> 
> 
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