Table contains 2x super Projections

kamil

Folks,

By quering projections table:
select * from projections where anchor_table_name='X' and is_super_projection='t';
i see that one of my tables contains 2 super projections.
Can this lead to some problems? Performance or other?

Jim_Knicely

A "superprojection" is simply a projection that includes all columns in an anchor table. You need at least one so that Vertica can service any SQL against the anchor table. However, you can have more than one "superprojection" where each can be tuned for a specific query type (i.e. have different sort orders). Keep in mind having more projections will adversely affect load times. If the 2 "superprojections" in your database on this table have the same sort order and segmentation, then you should drop one of them. You can check the PROJECTION_USAGE system table to find out which one is actually being used by Vertica.

See:
https://my.vertica.com/docs/9.0.x/HTML/index.htm#Authoring/SQLReferenceManual/SystemTables/MONITOR/PROJECTION_USAGE.htm

kamil

Thanks Jim!
Its clear now!