2011/6/22 aaron morton <aa...@thelastpickle.com> > I think I have to detail my configuration. On every server of my cluster, I > deploy : > - a Cassandra node > - a Tomcat instance > - the webapp, deployed on Tomcat > - Apache httpd, in front of Tomcat with mod_jakarta > > > You will have a bunch of services on the machine competing with each other > for resources (cpu, memory and network IO). It's not an approach I would > take. > > You will also tightly couple the front end HTTP capacity to the DB > capacity. e.g. consider what happens when a cassandra node is down for a > while, what does this mean for your ability to accept http connections? > If the Cassandra JVM is down, Tomcat and Httpd will continue to handle requests. And Pelops will redirect these requests to another Cassandra node on another server (maybe am I wrong with this assertion).
> > Requests from your web app may go to the local cassandra node, but thats > just the coordinator. They will be forwarded onto the replicas that contain > the data. > Yes, but as you notice before, this node can be down, so I will configure Pelops to redistribute requests on another node. So there is no strong couple between Cassandra and Tomcat ; It will works as if they was on different servers. > > Data are stored with RandomPartitionner, replication factor is 2. > > > RF 3 is the minimum RF you need to use for QUORUM to be less than the RF. > Thank you for this advice ; I will reconsider the RF, but for this time, I use only CL.ONE, not QUORUM. But it could change in a near future. > > In such case, do you advise me to store files in Cassandra ? > > > Depends on your scale, workload and performance requirements. I would do > some tests about how much data you expect to hold and what sort of workloads > you need to support. Personally I think files are best kept in a file > system, until a compelling reason is found to do other wise. > Thank you, I think that distributing files in the cluster with something like distributed file systems is a compelling reason to store files on Cassandra. I don't want to add another complex component to my arch. > > Hope that helps. > It does ! A lot ! Thank you. > ----------------- > Aaron Morton > Freelance Cassandra Developer > @aaronmorton > http://www.thelastpickle.com > > On 22 Jun 2011, at 20:23, Damien Picard wrote: > > >store your images / documents / etc. somewhere and reference them > >in Cassandra. That's the consensus that's been bandied about on this > >list quite frequently > > Thank you for your answers. > > I think I have to detail my configuration. On every server of my cluster, I > deploy : > - a Cassandra node > - a Tomcat instance > - the webapp, deployed on Tomcat > - Apache httpd, in front of Tomcat with mod_jakarta > > In front of these, I use a Round-Robin DNS load balancer which balance > request on every httpd. > Every Tomcat instance can access every Cassandra node, allowing them to > deal with every request. > Data are stored with RandomPartitionner, replication factor is 2. > > In my case, it would be very easy to store images in Cassandra because > these images will be accessible everywhere in my cluster. If I store images > in FileSystem, I have to replicate them manually (probably with a > distributed filesystem) on every server (quite complicated). This is why I > prefer to store files into Cassandra. > > According to Sylvain, the main thing to know is the max size of a file. In > so far as I am on a web purpose, I can define this max file size to 10 Mb > (HTTP POST max size) without disapointing my users.Furthermore, most of > these files will not exceed 2 or 3 Mb. In such case, do you advise me to > store files in Cassandra ? > > Thank you. > > 2011/6/22 Sylvain Lebresne <sylv...@datastax.com> > >> Let's be more precise in saying that this all depends on the >> expected size of the documents. If you know that the documents >> will be on the few hundreds kilobytes mark on average and >> no more than a few megabytes (say < 5MB, even though there is >> no magic number), then storing them as blob will work perfectly >> fine (which is not saying storing them externally with metadata in >> Cassandra won't, but using blobs can be simpler in some cases). >> >> I've very successfully stored tons of images as blobs in Cassandra. >> I just knew they couldn't get super big because the system wasn't >> allowing it. >> >> The point with the size being that each time you will get a document, >> Cassandra will have to load it (entirely) in memory to return it. >> >> -- >> Sylvain >> >> >> On Wed, Jun 22, 2011 at 9:22 AM, Sasha Dolgy <sdo...@gmail.com> wrote: >> > >> http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Storing-photos-images-docs-etc-td6078278.html >> > >> > Of significance from that link (which was great until feeling lucky >> > was removed...): >> > >> > Google of terms cassandra large files + feeling lucky >> > >> http://www.google.com/search?q=cassandra+large+files&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a >> > >> > Yields: >> > http://wiki.apache.org/cassandra/FAQ#large_file_and_blob_storage >> > >> > >> > --- store your images / documents / etc. somewhere and reference them >> > in Cassandra. That's the consensus that's been bandied about on this >> > list quite frequently. we employ a solution that uses Amazon S3 for >> > storage and Cassandra as the reference to the meta data and location >> > of the files. works a treat >> > >> > >> > On Wed, Jun 22, 2011 at 9:07 AM, Damien Picard <picard.dam...@gmail.com> >> wrote: >> >> Hi, >> >> >> >> I have to store some files (Images, documents, etc.) for my users in a >> >> webapp. I use Cassandra for all of my data and I would like to know if >> this >> >> is a good idea to store these files into blob on a Cassandra CF ? >> >> Is there some contraindications, or special things to know to achieve >> this ? >> >> >> >> Thank you >> > >> > > > > -- > Damien Picard > Axeiya Services : http://axeiya.com/ > gwt-ckeditor : http://code.google.com/p/gwt-ckeditor/ > Mon livre sur GWT : http://axeiya.com/index.php/ouvrage-gwt.html > > > -- Damien Picard Axeiya Services : http://axeiya.com/ gwt-ckeditor : http://code.google.com/p/gwt-ckeditor/ Mon livre sur GWT : http://axeiya.com/index.php/ouvrage-gwt.html
