Vertica - removing nodes from a database

raulk89

Hi
Vertica 10.1.0
Here, the P6 states

6. When warned that you must redesign your database and create projections that exclude the hosts you are going to drop, select Yes.

What does this actually mean. Does it mean, that I need to manually achieve this somehow (if, so, then how?), or will the admintools takes care this automatically..?

My point is, whenever I had 3 nodes, with k-safe 2, and I want to remove single node from database, then first I set k-safe to 0, then remove single node and then these remaining nodes need to recreate/refresh their projections so that instead of "segments spread across 3 nodes", these segments need to be spread across 2 remaining nodes. So that I have 2 segments instead of 3. --> How do I achieve that..?
Raul

Jim_Knicely

If you have three nodes and want to remove one, you still have to set K-Safety to 0 first:

Lowering The K-Safety Level To Allow For Node Removal

Once you've completed step 10 in the "Remove Hosts From the Database with Administration Tools" section of the doc page you specified, the projection segments that were located on the node you removed will have been distributed across the remaining 2 nodes. That is what is meant by "you must redesign your database and create projections that exclude the hosts you are going to drop". Vertica does it for you.

raulk89

If you have three nodes and want to remove one, you still have to set K-Safety to 0 first:

Yeah, that I did mention also: "...then first I set k-safe to 0, then remove single node and..."

That is what is meant by "you must redesign your database and create projections that exclude the hosts you are going to drop".

This "you must redesign..." got me confused, like I need to do this somehow myself.
But then I understand that vertica does that all for me.
So this step 10 could take quite a lot of time then, depending on how much data you have, correct..?
Regards
Raul

Jim_Knicely

I can understand the confusion about the "you" directive I will bring this up to the doc team. Thanks for the feedback!

And you are correct, the larger the data set the longer it will take to rebalance.

There are couple of "Best Practices" blog posts that can help!

Prepare Your Cluster for Rebalance
Understanding Rebalancing Part 1
Understanding Rebalancing Part 2

P.S. One of the awesome beneifits of Vertica Eon is that the need for a costly "Cluster Rebalance" after removing nodes is no longer necessary!

Vertica Architecture Eon Vs EnterpriseMode