How to find what node a key is on
Does anybody know if it's possible to find out what node a specific key/row lives on? We have a 30 node cluster and I'm curious how much faster it'll be to read data directly from the node that stores the data. We're using random partitioner, by the way. *Sameer Farooqui *Accenture Technology Labs
Re: How to find what node a key is on
Each row is stored on RF nodes, and your read will be sent to CL number of nodes. Messages only take a single hop from the coordinator to each node the read is performed on, so the networking overhead varies with the number of nodes involved in the request. There are man factors other than networking that influence the speed of a read request. There are features available to determine which nodes holds replicas for a particular key. AFAIK they are not intended for use by clients. Are you currently having problems with read performance ? Hope that helps. Aaron On 24 Mar 2011, at 11:53, Sameer Farooqui wrote: Does anybody know if it's possible to find out what node a specific key/row lives on? We have a 30 node cluster and I'm curious how much faster it'll be to read data directly from the node that stores the data. We're using random partitioner, by the way. Sameer Farooqui Accenture Technology Labs
Re: How to find what node a key is on
No problems with read performance, just curious about what kind of overhead was being added b/c we're doing read tests. If it's easy to figure out where the row is stored, I'd be interested in trying it. If not, don't worry about it. - Sameer On Wed, Mar 23, 2011 at 4:31 PM, aaron morton aa...@thelastpickle.comwrote: Each row is stored on RF nodes, and your read will be sent to CL number of nodes. Messages only take a single hop from the coordinator to each node the read is performed on, so the networking overhead varies with the number of nodes involved in the request. There are man factors other than networking that influence the speed of a read request. There are features available to determine which nodes holds replicas for a particular key. AFAIK they are not intended for use by clients. Are you currently having problems with read performance ? Hope that helps. Aaron On 24 Mar 2011, at 11:53, Sameer Farooqui wrote: Does anybody know if it's possible to find out what node a specific key/row lives on? We have a 30 node cluster and I'm curious how much faster it'll be to read data directly from the node that stores the data. We're using random partitioner, by the way. *Sameer Farooqui *Accenture Technology Labs
Re: How to find what node a key is on
On Wed, Mar 23, 2011 at 4:31 PM, aaron morton aa...@thelastpickle.com wrote: There are features available to determine which nodes holds replicas for a particular key. AFAIK they are not intended for use by clients. Specifically : http://wiki.apache.org/cassandra/JmxInterface#org.apache.cassandra.service.StorageService.Operations.getNaturalEndpoints Which is I think what Sameer was asking all along.. :) =Rob
Re: How to find what node a key is on
The logic to find the node is not complicated. You compute the MD5 hash of the key. Create sorted list of tokens assigned to the nodes in the ring. Find the first token greater than the hash. This is the first node. Next in the list is the replica, which depends on the RF. Now this is simple because this assumes SimpleStrategy for replica placement. For other strategies finding replicas will be more involved. Cassandra is a distributed databases. Each node is aware of the state of the cluster and token distribution. Moving the logic into client is possible but the benefits are way less compared to pain. At the same time doing it for a large cluster would be more painful. I would discourage you from going that route. Thanks, Naren On Wed, Mar 23, 2011 at 5:16 PM, Sameer Farooqui cassandral...@gmail.comwrote: No problems with read performance, just curious about what kind of overhead was being added b/c we're doing read tests. If it's easy to figure out where the row is stored, I'd be interested in trying it. If not, don't worry about it. - Sameer On Wed, Mar 23, 2011 at 4:31 PM, aaron morton aa...@thelastpickle.comwrote: Each row is stored on RF nodes, and your read will be sent to CL number of nodes. Messages only take a single hop from the coordinator to each node the read is performed on, so the networking overhead varies with the number of nodes involved in the request. There are man factors other than networking that influence the speed of a read request. There are features available to determine which nodes holds replicas for a particular key. AFAIK they are not intended for use by clients. Are you currently having problems with read performance ? Hope that helps. Aaron On 24 Mar 2011, at 11:53, Sameer Farooqui wrote: Does anybody know if it's possible to find out what node a specific key/row lives on? We have a 30 node cluster and I'm curious how much faster it'll be to read data directly from the node that stores the data. We're using random partitioner, by the way. *Sameer Farooqui *Accenture Technology Labs
