| 1:drop view if exists concurrent_drop_view cascade; |
| 1:create view concurrent_drop_view as select * from pg_class; |
| 1:select viewname from pg_views where viewname = 'concurrent_drop_view'; |
| |
| -- One transaction drops the view, and before it commits, another |
| -- transaction selects its definition from pg_views. The view is still |
| -- visible to the second transaction, but deparsing the view's |
| -- definition will block until the first transaction ends. And if the |
| -- first transaction committed, the definition cannot be fetched. |
| -- It's returned as NULL in that case. (PostgreSQL throws an ERROR, |
| -- but getting a spurious ERROR when all you do is query pg_views is |
| -- not nice.) |
| 1:begin; |
| 1:drop view concurrent_drop_view; |
| 2&:select viewname, definition from pg_views where viewname = 'concurrent_drop_view'; |
| -- wait till halts for AccessShareLock on QD |
| 3: SELECT wait_until_waiting_for_required_lock('concurrent_drop_view', 'AccessShareLock', -1); |
| 1:commit; |
| 2<: |
