Can I have ksafe as 2 on 4 node cluster

ersaurabhex

Number of nodes = 4
Ksafe = 2 (3 copy of data)
Data Rows :
A
B
C
D

Node 1:
A
D
C

Node 2:
B
A
D

Node 3:
C
A
B

Node 4:
D
C
B

With above combination, I can have all data available, even if any of two nodes went down.

Will I be allowed to do ksafe = 2 on 4 node cluster?

Jim_Knicely

Hi,

According to the documentation (and as seen in practice), regardless of the K-Safety value...

If half or more of the nodes in the database cluster fail, the database automatically shuts down even if all of the data in the database is available from replicas. This behavior prevents issues due to network partitioning.

See:
https://my.vertica.com/docs/9.1.x/HTML/index.htm#Authoring/ConceptsGuide/Components/K-Safety.htm

Jim_Knicely

Hi,

According to the documentation (and as seen in practice), regardless of K-Safety value...

If half or more of the nodes in the database cluster fail, the database automatically shuts down even if all of the data in the database is available from replicas. This behavior prevents issues due to network partitioning.

See:
https://my.vertica.com/docs/9.1.x/HTML/index.htm#Authoring/ConceptsGuide/Components/K-Safety.htm

Also note, Vertica won't let you set the K-Safety to 2 unless you have at least 5 nodes...

dbadmin=> \dt
No relations found.

dbadmin=> SELECT designed_fault_tolerance, current_fault_tolerance, node_count, node_down_count FROM system;
 designed_fault_tolerance | current_fault_tolerance | node_count | node_down_count
--------------------------+-------------------------+------------+-----------------
                        1 |                       1 |          4 |               0
(1 row)

dbadmin=> SELECT mark_design_ksafe(2);
                   mark_design_ksafe
-------------------------------------------------------
 Invalid K value: 2. Maximum K value for 4 nodes is: 1
(1 row)

See:
https://my.vertica.com/docs/9.1.x/HTML/index.htm#Authoring/AdministratorsGuide/ConfiguringTheDB/PhysicalSchema/DesigningForK-Safety.htm