The discussion revolves around a problem with a multisite instance where databases failed to migrate due to a PG::DuplicateColumn error. Initially, pfaffman suspected it was due to a column already existing, but later discovered that the issue was caused by SKIP_POST_DEPLOYMENT_MIGRATIONS being set, preventing previous migrations from running.
RGJ found a related GitHub commit that explains the problem, which is due to conflicting migrations trying to add the same columns. pfaffman confirmed that this explanation matches the issue he experienced.
Nick_Tomlinson is also experiencing the same issue and asks how to apply the fix from the GitHub commit to his Discourse instance.
I have a multisite instance in which a bunch of databases failed to migrate because
PG::DuplicateColumn: ERROR: column "bookmarkable_id" of relation "bookmarks" already exists
maybe I should go delete that column from that table in those databases?
looks like it was because previous migrations hadn’t run due to SKIP_POST_DEPLOYMENT_MIGRATIONS being set and previous migrations hadn’t finished.
I’ll delete this when I confirm that’s true…
@martin any ideas, may be related to the recent refactors?
Sorry for the false alarm. I so hate when I do this.
The issue was that I had SKIP_POST_DEPLOYMENT_MIGRATIONS: 1 set and then didn’t run multisite:migrate. After I did a `SKIP_POST_DEPLOYMENT_MIGRATIONS=- multisite:migrate’ I was then able to bootstrap.
I just need to fix my tooling for multisite to run the migration after cranking up the new semi-migrated container.
But strange. Recovering from failed/partially applied upgrade seems to have the same issue and it appears to be a standard install.
I would’ve replied to this post, but figured it was the same symptom of a different problem. 
I admittedly don’t know enough to confirm either way…
Seems to be related to DEV: Re-add polymorphic bookmark columns (#16261) · discourse/discourse@8040b95 · GitHub
This commit is a redo of 2f1ddadff7dd47f824070c8a3f633f00a27aacde
which we reverted because it blew up an internal CI check. I looked
into it, and it happened because the old migration to add the bookmark
columns still existed, and those columns were dropped in a post migrate,
so the two migrations to add the columns were conflicting before
the post migrate was run.
Wow. That seems to explain it.
Any update on this?
Mine is coming up with the same issue.
How would i copy this git into my discourse?