> Multiple concurrent index creations on a single table will not return from either CREATE INDEX CONCURRENTLY ... statement until the slowest one completes. I

> Multiple concurrent index creations on a single table will not return from either CREATE INDEX CONCURRENTLY ... statement until the slowest one completes. I am not sure this is true anymore, or at least, it was improved in v14 to only apply when "the indexes involved are partial or have columns that are not simple column references." [1] Another thing worth noting here is that the exclusive locks taken on system catalogues during a DDL change also replicate to your replicas (necessarily, ha!) and they will have the same behavior described, i.e., they will line up behind queries. So for instance if you run long ETL queries against a replica, the DDL lock will line up behind it and no other queries can run until the ETL query is done and the DDL lock goes through. [1] https://www.postgresql.org/docs/14/sql-createindex.html https://www.postgresql.org/docs/14/sql-createindex.html