Projection - OFFSET setting

[Ivy]

I am looking at a DIM table in the database. There are two pretty much identical projections. The first one is "SEGMENTED BY hash(date_dim.date_key) ALL NODES " and the second is "SEGMENTED BY hash(date_dim.date_key) ALL NODES OFFSET 1." Does anybody know the difference between the OFFSET 0 and OFFSET 1 and why we need two projections for one dim table? Any help is greatly appreciated!

[id10t]

Hi!

Read in docs: High Availability Through Projections

Buddy Projections (Segmented Projections)

Vertica creates buddy projections, which are copies of segmented projections that are distributed across database nodes. (See Projection Segmentation.) Vertica ensures that segments that contain the same data are distributed to different nodes. This ensures that if a node goes down, all the data is available on the remaining nodes. Vertica distributes segments to different nodes by using offsets. For example, segments that comprise the first buddy projection (A_BP1) would be offset from projection A by one node and segments from the second buddy projection (A_BP2) would be offset from projection A by two nodes.

[Ivy]

Thank you kindly for your explanation sKwa!