Designing for K-safety
Vertica recommends that all production databases have a minimum K-safety of one (K=1). Valid K-safety values for production databases are 1 and 2. Non-production databases do not have to be K-safe and can be set to 0.
A K-safe database must have at least three nodes, as shown in the following table:
| K-safety level | Number of required nodes |
|---|---|
| 1 | 3+ |
| 2 | 5+ |
Note
Vertica only supports K-safety levels 1 and 2.You can set K-safety to 1 or 2 only when the physical schema design meets certain redundancy requirements. See Requirements for a K-safe physical schema design.
Using Database Designer
To create designs that are K-safe, Vertica recommends that you use the Database Designer. When creating projections with Database Designer, projection definitions that meet K-safe design requirements are recommended and marked with a K-safety level. Database Designer creates a script that uses the
MARK_DESIGN_KSAFE function to set the K-safety of the physical schema to 1. For example:
=> \i VMart_Schema_design_opt_1.sql
CREATE PROJECTION
CREATE PROJECTION
mark_design_ksafe
----------------------
Marked design 1-safe
(1 row)
By default, Vertica creates K-safe superprojections when database K-safety is greater than 0.
Monitoring K-safety
Monitoring tables can be accessed programmatically to enable external actions, such as alerts. You monitor the K-safety level by querying the
SYSTEM table for settings in columns DESIGNED_FAULT_TOLERANCE and CURRENT_FAULT_TOLERANCE.
Loss of K-safety
When K nodes in your cluster fail, your database continues to run, although performance is affected. Further node failures could potentially cause the database to shut down if the failed node's data is not available from another functioning node in the cluster.