How to model hierarchical structure?
Like Category, Taxonomy, or folder/file, there will be multiple level hierarchical relationship. How to model it in Cassandra? Serialize all the parent id and the item id together as the key? How to model it when one child has many parents?
Re: How to model hierarchical structure?
use the parent as column family and the child as the column under the column family if this is two-level. And you can use the super-column if there are more than two-levels On Sat, Mar 6, 2010 at 1:31 AM, HubertChang hui...@gmail.com wrote: For examples, like tags, many parents to many children. -- View this message in context: http://n2.nabble.com/How-to-model-hierarchical-structure-tp4685633p4685649.html Sent from the cassandra-user@incubator.apache.org mailing list archive at Nabble.com. -- Best Regards Jeff Zhang
Re: Incr/Decr Counters in Cassandra
Werner Vogels had a recent post around Amazon's support for primitives in SimpleDB that can be used to build counters. Given the historical influences from Amazon s Dynamo to Cassandra I would think a similar approach might work well. http://www.allthingsdistributed.com/2010/02/strong_consistency_simpledb.html BTW...I would be VERY interested in such support. -- View this message in context: http://n2.nabble.com/Incr-Decr-Counters-in-Cassandra-tp3948361p4686353.html Sent from the cassandra-user@incubator.apache.org mailing list archive at Nabble.com.
Re: Unreliable transport layer
We have observed this. But in practice it doesn't cause any deleterious effects. IMHO detecting false failures of nodes is the most dangerous thing that could result from this kind of behavior. But that is why we have an Accrual FD which reacts and adjusts to these conditions. But having said that moving TCP is not a bad option at all at relatively small scale. Cheers Avinash On Fri, Mar 5, 2010 at 4:54 PM, Ashwin Jayaprakash ashwin.jayaprak...@gmail.com wrote: Hey guys! I have a simple question. I'm a casual observer, not a real Cassandra user yet. So, excuse my ignorance. I see that the Gossip feature uses UDP. I was curious to know if you guys faced issues with unreliable transports in your production clusters? Like faulty switches, dropped packets etc during heavy network loads? If I'm not mistaken are all client reads/writes doing point-to-point over TCP? Thanks, Ashwin.
Re: Cassandra hardware - balancing CPU/memory/iops/disk space
Eric, Couple of thoughts: 1. Hardware Definitely dual quad core 12 X 4 DIMMS. This is the sweet spot for memory. I have many machines with this config and some with the 12 X 2 configs I haven¹t found the need for SATA and the higher price Make sure you get good NICs Are you using any virtualization layer ? I assume these are bare metal with Ubuntu or RedHat. 2. Scaling Naturally you should look at horizontal scaling than vertical. An estimate of the application characteristics and data properties would be helpful to get a first estimate I think eventually you will end up with multiple boxes anyway, so my philosophy has been to buy multiple optimal boxes We are working on scaling characteristics (memory, network and storage), unfortunately way too early to make any inferences HTH. Cheers k/ On 3/5/10 Fri Mar 5, 10, Rosenberry, Eric eric.rosenbe...@iovation.com wrote: I am looking for advice from others that are further along in deploying Cassandra in production environments than we are. I want to know what you are finding your bottlenecks to be. I would feel silly purchasing dual processor quad core 2.93ghz Nehalem machines with 192 gigs of RAM just to find out that the two local SATA disks kept all that CPU and RAM from being useful (clearly that example would be a dumb). I need to spec out hardware for an ³optimal² Cassandra node (though our read/write characteristics are not yet fully defined so let¹s go with an ³average² configuration). My main concern is finding the right balance of: ·Available CPU ·RAM amount ·RAM speed (think Nehalem architecture where memory comes in a few speeds, though I doubt this is much of a concern as it is mainly dictated by which processor you buy and how many slots you populate) ·Total iops available (i.e. number of disks) ·Total disk space available (depending on the ratio of iops/space deciding on SAS vs. SATA and various rotational speeds) My current thinking is 1U boxes with four 3.5 inch disks since that seems to be a readily available config. One big question is should I go with a single processor Nehalem system to go with those four disks, or would two CPU¹s be useful, and also, how much RAM is appropriate to match? I am making the assumption that Cassandra nodes are going to be disk bound as they must do a random read to answer any given query (i.e. indexes in RAM, but all data lives on disk?). The other big decision is what type of hard disks others are finding to provide the optimal ratio of iops to available space? SAS or SATA? And what rotational speed? Let me throw out here an actual hardware config and feel free to tell me the error of my ways: ·A SuperMicro SuperServer 6016T-NTRF configured as follows: o 2.26 ghz E5520 dual processor quad core hyperthreaded Nehalem architecture (this proc provides a lot of bang for the buck, faster procs get more expensive quickly) o Qty 12, 4 gig 1066mhz DIMMS for a total of 48 gigs RAM (the 4 gig DIMMS seem to be the price sweet spot) o Dual on board 1 gigabit NIC¹s (perhaps one for client connections and the other for cluster communication?) o Dual power supplies (I don¹t want to lose half my cluster due to a failure on one power leg) o 4x 1TB SATA disks (this is a complete SWAG) o No RAID controller (all just single individual disks presented to the OS) Though is there any down side to using a RAID controller with RAID 0 (perhaps one single disk for the log for sequential io¹s, and 3x disks in a stripe for the random io¹s) o The on-board IPMI based OOB controller (so we can kick the boxes remotely if need be) ·http://www.supermicro.com/products/system/1U/6016/SYS-6016T-NTRF.cfm I can¹t help but think the above config has way too much RAM and CPU and not enough iops capacity. My understanding is that Cassandra does not cache much in RAM though? Any thoughts are appreciated. Thanks. -Eric ___ Eric Rosenberry Sr. Infrastructure Architect | Chief Bit Plumber iovation 111 SW Fifth Avenue Suite 3200 Portland, OR 97204 www.iovation.com http://www.iovation.com/ The information contained in this email message may be privileged, confidential and protected from disclosure. If you are not the intended recipient, any dissemination, distribution or copying is strictly prohibited. If you think that you have received this email message in error, please notify the sender by reply email and delete the message and any attachments.
Re: How to model hierarchical structure?
This really depends on the operations you want to optimize for. What's important to you? Aggregate queries? Finding children/siblings/ancestors? Reorganizing the tree/hierarchy? For Cassandra, you really need to spend time thinking about how you'll be accessing things and design for that. If it's a 2-3 level hierarchy, then straight forward approaches like what Jeff suggested seem logical. Otherwise, I'd say if you've got an arbitrary-level hierarchy, then you'll have to think about how to efficiently adapt one of the usual suspects for this stuff (adjacency lists, nested sets, materialized paths, etc.). I, for one, would be interested in knowing if anyone else's experienced with this kind of stuff in Cassandra. http://stackoverflow.com/questions/192220/what-is-the-most-efficient-elegant-way-to-parse-a-flat-table-into-a-tree/192462#192462 and the like might be good places to start. On Sat, Mar 6, 2010 at 2:13 AM, Jeff Zhang zjf...@gmail.com wrote: use the parent as column family and the child as the column under the column family if this is two-level. And you can use the super-column if there are more than two-levels On Sat, Mar 6, 2010 at 1:31 AM, HubertChang hui...@gmail.com wrote: For examples, like tags, many parents to many children. -- View this message in context: http://n2.nabble.com/How-to-model-hierarchical-structure-tp4685633p4685649.html Sent from the cassandra-user@incubator.apache.org mailing list archive at Nabble.com. -- Best Regards Jeff Zhang -- jeande...@6coders.com (917) 951-0636 This email and any files transmitted with it are confidential and intended solely for the use of the individual to whom they are addressed. If you have received this email in error please notify the system manager. This message contains confidential information and is intended only for the individual named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately by e-mail if you have received this e-mail by mistake and delete this e-mail from your system. If you are not the intended recipient you are notified that disclosing, copying, distributing or taking any action in reliance on the contents of this information is strictly prohibited.
