Rados consistency model

Rados consistency model

[Rutger ter Borg]

Dear list,

I have a question regarding concurrency guarantees of Rados. Suppose I 
have two nodes, say A and B, both running a process, and both using the 
same rados storage pool, maybe connected through different OSDs. Suppose 
node A updates an object in the storage pool, and after completion 
immediately notifies B (through its own messaging layer) that that 
specific object has been updated. Then, can I assume that, if B re-reads 
that object, it will always get the updated one? If not, what would be 
the recommended way of notifying B?

IOW, what kind of consistency model should I assume?

Thanks,

Rutger

Re: Rados consistency model

[Samuel Just]

You can expect read-after-write on any object.  That is, once the
write is complete, any subsequent reader will see the result.
-Sam

On Tue, Dec 18, 2012 at 12:51 AM, Rutger ter Borg <rutger@terborg.net> wrote:
>
> Dear list,
>
> I have a question regarding concurrency guarantees of Rados. Suppose I have
> two nodes, say A and B, both running a process, and both using the same
> rados storage pool, maybe connected through different OSDs. Suppose node A
> updates an object in the storage pool, and after completion immediately
> notifies B (through its own messaging layer) that that specific object has
> been updated. Then, can I assume that, if B re-reads that object, it will
> always get the updated one? If not, what would be the recommended way of
> notifying B?
>
> IOW, what kind of consistency model should I assume?
>
> Thanks,
>
> Rutger
>
>
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