In this case, the load balancer has to detect (or is configured) that the server is down and does not route request to this one anymore.
2011/6/22 aaron morton <aa...@thelastpickle.com> > 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). > >> > I was thinking of the server been turned off / broken / rebooting / > disconnected from the network / taken out of rotation for maintenance. There > are lots of reasons for a server to not be doing what it should be. > > > ----------------- > Aaron Morton > Freelance Cassandra Developer > @aaronmorton > http://www.thelastpickle.com > > On 22 Jun 2011, at 23:10, Damien Picard wrote: > > > > 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 > > > -- 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
