Forum: VoltDB Architecture

Post: How to avoid a cluster with only one database COPY

How to avoid a cluster with only one database COPY
gambitg
Sep 7, 2011
It seems k-safety serves two purpose:
1. To define number of copies of database
2. To define the max number of nodes that can be down before VoltDB brings the cluster down.


How can I decouple the two values ? Specifically I wish to have 2 copies of my data but the cluster to be brought down when only one copy is left over. Is it possible to accomplish this ?


Thanks.
k-safety
rbetts
Sep 7, 2011
These two concepts can not be decoupled in Volt (at least not as a matter of configuration). Note that voltdb doesn't replicate Nodes - it replicates partitions. As nodes fail, you may have 1 copy of partiton A, but perhaps 2 copies of partiton B (because of how we assign partition replicas to nodes).


Finding a point in time, across failures, at which exactly one copy of the DB remains doesn't really match how VoltDB works.


To do you what you want, you would have to monitor the database externally and shutdown the cluster after your monitor observed some number of failures.