> 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 >
