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From Leigh Stewart <lstew...@twitter.com.INVALID>
Subject Re: Proxy Client - Batch Ordering / Commit
Date Thu, 06 Oct 2016 15:20:11 GMT
Ah- yes good point (to be clear we're not using the proxy this way today).
But I think this is tricky to completely solve even if there's a way for
the proxy node to ensure failure within some timeframe.
What if the request is stuck somewhere in the network (as unlikely as that
sounds?) Or ex. at the very top of the jvm network stack, delayed by gc?

Cancellations wont help here. The best approach - fencing off the stream by
recovering it in the reader - wont help if the proxy will simply apply the
delayed write afterwards.

As to whether there's some way we could support this, will have to think
about it more, but using the core library directly is usually better in
cases where strict consistency and ordering are required on the *write*
side.

Due to the source of the
> data (HBase Replication), we cannot guarantee that a single partition will
> be owned for writes by the same client.


Do you mean you *need* to support multiple writers issuing interleaved
writes or is it just that they might sometimes interleave writes and you
don't care?

If you expect to have a single writer most of the time maybe the core
library would be better for you.

On Wed, Oct 5, 2016 at 2:58 PM, Cameron Hatfield <kinguy@gmail.com> wrote:

> Basically, its point 6 above. What ends up being the timeout for me to
> ensure that a result is committed or not, so that I guarantee a read
> actually gives me the last value??
>
>
> -Cameron
>
> On Wed, Oct 5, 2016 at 2:51 PM, Leigh Stewart <lstewart@twitter.com.invalid
> >
> wrote:
>
> > There is no automatic dedup or key based update.
> >
> > In failure scenarios you would need to recover by reading the latest id,
> > and retry based on this.
> >
> > Would that work?
> >
> > On Wed, Oct 5, 2016 at 2:02 PM, Cameron Hatfield <kinguy@gmail.com>
> wrote:
> >
> > > Main question I have then is what happens in the case of retry due to
> > > network failure, where the client doesn't get a success response, but
> it
> > > succeeds / will succeed proxy server side?
> > > What do I have to ensure that no duplicates are written to
> distributedlog
> > > in such a case?
> > >
> > > -Cameron
> > >
> > > On Wed, Oct 5, 2016 at 11:33 AM, Leigh Stewart
> > > <lstewart@twitter.com.invalid
> > > > wrote:
> > >
> > > > >
> > > > > So, my basic question is if this is currently possible in the
> proxy?
> > I
> > > > > don't believe it gives these guarantees as it stands today, but I
> am
> > > not
> > > > > 100% of how all of the futures in the code handle failures.
> > > > >
> > > >
> > > > As long as you use this method
> > > > <http://distributedlog.incubator.apache.org/docs/
> > > latest/tutorials/basic-4>
> > > > to write this is possible.
> > > >
> > > > The writeBulk is not atomic and we will probably deprecated it at
> some
> > > > point.
> > > >
> > > > If not, where in the code would be the relevant places to add the
> > ability
> > > > > to do this, and would the project be interested in a pull request?
> > > >
> > > >
> > > > Does the example linked above meet your requirements?
> > > >
> > > > Thx
> > > >
> > > > On Tue, Oct 4, 2016 at 12:39 PM, Cameron Hatfield <kinguy@gmail.com>
> > > > wrote:
> > > >
> > > > > I have a question about the Proxy Client. Basically, for our use
> > cases,
> > > > we
> > > > > want to guarantee ordering at the key level, irrespective of the
> > > ordering
> > > > > of the partition it may be assigned to as a whole. Due to the
> source
> > of
> > > > the
> > > > > data (HBase Replication), we cannot guarantee that a single
> partition
> > > > will
> > > > > be owned for writes by the same client. This means the proxy client
> > > works
> > > > > well (since we don't care which proxy owns the partition we are
> > writing
> > > > > to).
> > > > >
> > > > >
> > > > > However, the guarantees we need when writing a batch consists of:
> > > > > Definition of a Batch: The set of records sent to the writeBatch
> > > endpoint
> > > > > on the proxy
> > > > >
> > > > > 1. Batch success: If the client receives a success from the proxy,
> > then
> > > > > that batch is successfully written
> > > > >
> > > > > 2. Inter-Batch ordering : Once a batch has been written
> successfully
> > by
> > > > the
> > > > > client, when another batch is written, it will be guaranteed to be
> > > > ordered
> > > > > after the last batch (if it is the same stream).
> > > > >
> > > > > 3. Intra-Batch ordering: Within a batch of writes, the records will
> > be
> > > > > committed in order
> > > > >
> > > > > 4. Intra-Batch failure ordering: If an individual record fails to
> > write
> > > > > within a batch, all records after that record will not be written.
> > > > >
> > > > > 5. Batch Commit: Guarantee that if a batch returns a success, it
> will
> > > be
> > > > > written
> > > > >
> > > > > 6. Read-after-write: Once a batch is committed, within a limited
> > > > time-frame
> > > > > it will be able to be read. This is required in the case of
> failure,
> > so
> > > > > that the client can see what actually got committed. I believe the
> > > > > time-frame part could be removed if the client can send in the same
> > > > > sequence number that was written previously, since it would then
> fail
> > > and
> > > > > we would know that a read needs to occur.
> > > > >
> > > > >
> > > > > So, my basic question is if this is currently possible in the
> proxy?
> > I
> > > > > don't believe it gives these guarantees as it stands today, but I
> am
> > > not
> > > > > 100% of how all of the futures in the code handle failures.
> > > > > If not, where in the code would be the relevant places to add the
> > > ability
> > > > > to do this, and would the project be interested in a pull request?
> > > > >
> > > > >
> > > > > Thanks,
> > > > > Cameron
> > > > >
> > > >
> > >
> >
>

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