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From Lorenzo Fundaró <lorenzo.fund...@dawandamail.com>
Subject Re: deploy solr on cloud providers
Date Wed, 06 Jul 2016 09:30:49 GMT
On 6 July 2016 at 00:00, Tomás Fernández Löbbe <tomasflobbe@gmail.com>
wrote:

> The leader will do the replication before responding to the client, so lets
> say the leader gets to update it's local copy, but it's terminated before
> sending the request to the replicas, the client should get either an HTTP
> 500 or no http response. From the client code you can take action (log,
> retry, etc).
>

If this true then whenever I ask for min_rf having three nodes (1 leader +
2 replicas)
I should get rf = 3, but in reality i don't.


> The "min_rf" is useful for the case where replicas may be down or not
> accessible. Again, you can use this for retrying or take any necessary
> action on the client side if the desired rf is not achieved.
>


I think both paragraphs are contradictory. If the leader does the
replication before responding to the client, then
why is there a need to use the min_rf ? I don;t think is true that you get
a 200 when the update has been passed to all replicas.

The thing is that, when you have persistent storage yo shouldn't worry
about this because you know when the node comes back
the rest of the index will be sync, the problem is when you don't have
persistent storage. For my particular case I have to be extra careful and
always
make sure that all my replicas have all the data I sent.


> Tomás
>
> On Tue, Jul 5, 2016 at 11:39 AM, Lorenzo Fundaró <
> lorenzo.fundaro@dawandamail.com> wrote:
>
> > @Tomas and @Steven
> >
> > I am a bit skeptical about this two statements:
> >
> > If a node just disappears you should be fine in terms of data
> > > availability, since Solr in "SolrCloud" replicates the data as it comes
> > it
> > > (before sending the http response)
> >
> >
> > and
> >
> > >
> > > You shouldn't "need" to move the storage as SolrCloud will replicate
> all
> > > data to the new node and anything in the transaction log will already
> be
> > > distributed through the rest of the machines..
> >
> >
> > because according to the official documentation here
> > <
> >
> https://cwiki.apache.org/confluence/display/solr/Read+and+Write+Side+Fault+Tolerance
> > >:
> > (Write side fault tolerant -> recovery)
> >
> > If a leader goes down, it may have sent requests to some replicas and not
> > > others. So when a new potential leader is identified, it runs a synch
> > > process against the other replicas. If this is successful, everything
> > > should be consistent, the leader registers as active, and normal
> actions
> > > proceed
> >
> >
> > I think there is a possibility that an update is not sent by the leader
> but
> > is kept in the local disk and after it comes up again it can sync the
> > non-sent data.
> >
> > Furthermore:
> >
> > Achieved Replication Factor
> > > When using a replication factor greater than one, an update request may
> > > succeed on the shard leader but fail on one or more of the replicas.
> For
> > > instance, consider a collection with one shard and replication factor
> of
> > > three. In this case, you have a shard leader and two additional
> replicas.
> > > If an update request succeeds on the leader but fails on both replicas,
> > for
> > > whatever reason, the update request is still considered successful from
> > the
> > > perspective of the client. The replicas that missed the update will
> sync
> > > with the leader when they recover.
> >
> >
> > They have implemented this parameter called *min_rf* that you can use
> > (client-side) to make sure that your update was replicated to at least
> one
> > replica (e.g.: min_rf > 1).
> >
> > This is why my concern about moving storage around, because then I know
> > when the shard leader comes back, solrcloud will run sync process for
> those
> > documents that couldn't be sent to the replicas.
> >
> > Am I missing something or misunderstood the documentation ?
> >
> > Cheers !
> >
> >
> >
> >
> >
> >
> >
> > On 5 July 2016 at 19:49, Davis, Daniel (NIH/NLM) [C] <
> daniel.davis@nih.gov
> > >
> > wrote:
> >
> > > Lorenzo, this probably comes late, but my systems guys just don't want
> to
> > > give me real disk.   Although RAID-5 or LVM on-top of JBOD may be
> better
> > > than Amazon EBS, Amazon EBS is still much closer to real disk in terms
> of
> > > IOPS and latency than NFS ;)    I even ran a mini test (not an official
> > > benchmark), and found the response time for random reads to be better.
> > >
> > > If you are a young/smallish company, this may be all in the cloud, but
> if
> > > you are in a large organization like mine, you may also need to allow
> for
> > > other architectures, such as a "virtual" Netapp in the cloud that
> > > communicates with a physical Netapp on-premises, and the
> > throughput/latency
> > > of that.   The most important thing is to actually measure the numbers
> > you
> > > are getting, both for search and for simply raw I/O, or to get your
> > > systems/storage guys to measure those numbers.     If you get your
> > > systems/storage guys to just measure storage - you will want to care
> > about
> > > three things for indexing primarily:
> > >
> > >         Sequential Write Throughput
> > >         Random Read Throughput
> > >         Random Read Response Time/Latency
> > >
> > > Hope this helps,
> > >
> > > Dan Davis, Systems/Applications Architect (Contractor),
> > > Office of Computer and Communications Systems,
> > > National Library of Medicine, NIH
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: Lorenzo Fundaró [mailto:lorenzo.fundaro@dawandamail.com]
> > > Sent: Tuesday, July 05, 2016 3:20 AM
> > > To: solr-user@lucene.apache.org
> > > Subject: Re: deploy solr on cloud providers
> > >
> > > Hi Shawn. Actually what im trying to find out is whether this is the
> best
> > > approach for deploying solr in the cloud. I believe solrcloud solves a
> > lot
> > > of problems in terms of High Availability but when it comes to storage
> > > there seems to be a limitation that can be workaround of course but
> it's
> > a
> > > bit cumbersome and i was wondering if there is a better option for this
> > or
> > > if im missing something with the way I'm doing it. I wonder if there
> are
> > > some proved experience about how to solve the storage problem when
> > > deploying in the cloud. Any advise or point to some enlightening
> > > documentation will be appreciated. Thanks.
> > > On Jul 4, 2016 18:27, "Shawn Heisey" <apache@elyograg.org> wrote:
> > >
> > > > On 7/4/2016 10:18 AM, Lorenzo Fundaró wrote:
> > > > > when deploying solr (in solrcloud mode) in the cloud one has to
> take
> > > > > care of storage, and as far as I understand it can be a problem
> > > > > because the storage should go wherever the node is created. If we
> > > > > have for example, a node on EC2 with its own persistent disk, this
> > > > > node happens to be the leader and at some point crashes but
> couldn't
> > > > > make the replication of the data that has in the transaction log,
> > > > > how do we do in that case ? Ideally the new node must use the
> > > > > leftover data that the death node left, but this is a bit
> cumbersome
> > > > > in my opinion. What are the best practices for this ?
> > > >
> > > > I can't make any sense of this.  What is the *exact* problem you need
> > > > to solve?  The details can be very important.
> > > >
> > > > We might be dealing with this:
> > > >
> > > > http://people.apache.org/~hossman/#xyproblem
> > > >
> > > > Thanks,
> > > > Shawn
> > > >
> > > >
> > >
> >
> >
> >
> > --
> >
> > --
> > Lorenzo Fundaro
> > Backend Engineer
> > E-Mail: lorenzo.fundaro@dawandamail.com
> >
> > Fax       + 49 - (0)30 - 25 76 08 52
> > Tel        + 49 - (0)179 - 51 10 982
> >
> > DaWanda GmbH
> > Windscheidstraße 18
> > 10627 Berlin
> >
> > Geschäftsführer: Claudia Helming und Niels Nüssler
> > AG Charlottenburg HRB 104695 B http://www.dawanda.com
> >
>



-- 

-- 
Lorenzo Fundaro
Backend Engineer
E-Mail: lorenzo.fundaro@dawandamail.com

Fax       + 49 - (0)30 - 25 76 08 52
Tel        + 49 - (0)179 - 51 10 982

DaWanda GmbH
Windscheidstraße 18
10627 Berlin

Geschäftsführer: Claudia Helming und Niels Nüssler
AG Charlottenburg HRB 104695 B http://www.dawanda.com

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