Hi,
As we know postgres using high level lock when do alter table or other ddl commands, It will block any dml operation, while it also will block by long term dml operation. Like what discuss as follow : https://dba.stackexchange.com/questions/293992/make-alter-table-wait-for-lock-without-blocking-anything-else. I know that postgres try to avoid rewrite table when alter table happen , and so far, it support serveral ddl using concurrently feature, Like create indexes. But like alter table add/drop colum, alter column type, it also will trigger rewrtie table . Long term block will make application offline in long times. So is there any plan to support these ddl online and lock free？if not could you explain the technological difficulty ？ Thanks and wating your respond!
