On Fri, 29 Jun 2018, kefu chai wrote:
> i am adding interface for seastar to ObjectStore. but the ObjectStore
> works in a completely different way than an "ordinary" seastar app
> does. we use following pattern when serving write requests to
> ObjectStore:
>
> 1. prepare a transaction named txn.
> 2. hook callbacks to the transaction using txn.register_on_{applied,commit}
> 3. queue the transaction using store->queue_transaction(collection, txn)
> 4. the registered callbacks will be called in the ObjectStore's
> execution thread or separated finisher thread.
>
> does it make sense if we expose a method like
>
> seastar::future<> commit_transaction(collection, txn)
This makes sense to me. I defer to your judgement, though!
> which allows the caller to wait on the completion of commit, and to
> expect an exception if the commit fails somehow?
>
> currently, both FileStore and BlueStore are driven by Finishers and
> ThreadPools, in other words, they live in alien threads. we can always
> hook a wrapper functor will submit a continuation upon completion of
> commit or applied to reactor from where the original
> {queue,submit}_transactions() was called.
>
> but in long term, Seastore[0] will use run-to-completion model
> whenever possible. the new methods added to ObjectStore also helps us
> to shape Seastore.
>
> thoughts?
I think we will eventually want a wrapper around the old threaded
ObjectStore methods that exposes a call like the above (and similar
read-side methods) using the alien threads, but I wouldn't design the
interface around that.
sage
>
> ---
> [0] http://docs.ceph.com/docs/master/dev/seastore/
>
> --
> Regards
> Kefu Chai
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