Number of projections needed for k safety

Moderator: NorbertKrupa

Post Reply
User avatar
piglet
Beginner
Beginner
Posts: 45
Joined: Tue Feb 07, 2012 4:04 pm

Number of projections needed for k safety

Post by piglet » Thu Dec 11, 2014 6:11 pm

Hi,

I have a question about the number of projections needed for k safety. There seems to be a discrepancy in the documentation.

First it says in the "Designing Segmented Projections for K-Safety" section:
Create segmented buddy projections for each of these projections. The total number of projections in a buddy set must be two for a K=1 database or three for a K=2 database.
To me that says there are a total of two segmented projections for k=1...

But in the next section telling us how to segment projections it says:
You can segment projections across all the nodes, or just the number of nodes necessary to maintain K-safety, either three for a K=1 database or five for a K=2 database
To me that says there are a total of three segmented projections for k=1...

Which is correct? Or am misunderstanding the concept?

NorbertKrupa
GURU
GURU
Posts: 527
Joined: Tue Oct 22, 2013 9:36 pm
Location: Chicago, IL
Contact:

Re: Number of projections needed for k safety

Post by NorbertKrupa » Thu Dec 11, 2014 6:26 pm

What you see in the second section is that you need a minimum of 3 nodes for a K-Safety level of 1, and a minimum of 5 nodes for a K-Safety level of 2. This means that when you're creating a projection, you can specify which nodes will contain the projections.

By default, projections in a K-Safe database will automatically have a buddy projection that is offset to the next node.

In the below image with a K-Safety 1 database, you can see how the buddy projections are offset:

Image
Each of the nodes contains buddy projections for the data stored in the next higher node (node 1 has buddy projections for node 2, node 2 has buddy projections for node 3, etc.)
Take a look at the documentation on K-Saftey to see if it clears it up.
Checkout vertica.tips for more Vertica resources.

User avatar
piglet
Beginner
Beginner
Posts: 45
Joined: Tue Feb 07, 2012 4:04 pm

Re: Number of projections needed for k safety

Post by piglet » Thu Dec 11, 2014 7:02 pm

Hmm. The picture posted shows 5 nodes and 5 buddy projections for k=1... :?

Buddy Projection = 1
Buddy Projection = 2
Buddy Projection = 3
Buddy Projection = 4
Buddy Projection = 5

NorbertKrupa
GURU
GURU
Posts: 527
Joined: Tue Oct 22, 2013 9:36 pm
Location: Chicago, IL
Contact:

Re: Number of projections needed for k safety

Post by NorbertKrupa » Thu Dec 11, 2014 7:34 pm

That's right. Which part are you confused about?
Checkout vertica.tips for more Vertica resources.

Post Reply

Return to “New to Vertica”