Projections require manually triggered refresh?

abtsantosbenten

Do projections require manual refresh? Are they not automatically updated during DML transactions?

Jim_Knicely

Projections do not require manual refresh following DML operations. A projection refresh is only necessary after creating a new one.

See:
https://www.vertica.com/docs/9.2.x/HTML/Content/Authoring/AdministratorsGuide/Projections/UpdatingProjectionsUsingRefresh.htm

abtsantosbenten

Thanks. So, does this mean there's no need to check for stale projections?

Jim_Knicely

No. It's very important to make sure all projections are "up to date".

This query should always return 0:

dbadmin=> SELECT COUNT(*) FROM projections WHERE NOT is_up_to_date;
 COUNT
-------
     0
(1 row)

Otherwise your AHM will fall behind and not advance.

See:
https://www.vertica.com/blog/ancient-history-mark-not-advancing/

abtsantosbenten

what causes projections to become stale? sorry for asking this, but I am trying to find information from the documentation, but I couldn't find any.