woodlouse just showed a failure that looked a bit familiar: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=woodlouse&dt=2018-04-17%2016%3A42%3A43
I trawled the buildfarm logs for similar failures, and there are several: sysname | snapshot | stage | l -----------+---------------------+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------ whelk | 2018-03-28 05:41:30 | Check | 2018-03-28 07:52:26.987 CEST [4928:6] DETAIL: Failed process was running: ALTER TABLE itest13 ADD COLUMN c int GENERATED BY DEFAULT AS IDENTITY;\r conchuela | 2018-04-03 10:00:00 | Check | 2018-04-03 12:11:47.520 CEST [5ac35311.5248:5] DETAIL: Failed process was running: ALTER TABLE itest13 ADD COLUMN b int GENERATED BY DEFAULT AS IDENTITY; gharial | 2018-04-10 00:32:08 | Check | 2018-04-09 18:59:39.075 MDT [5acc0b05.32ea:5] DETAIL: Failed process was running: ALTER TABLE itest13 ADD COLUMN b int GENERATED BY DEFAULT AS IDENTITY; whelk | 2018-04-14 19:41:24 | Check | 2018-04-14 21:52:07.700 CEST [3760:6] DETAIL: Failed process was running: ALTER TABLE itest13 ADD COLUMN c int GENERATED BY DEFAULT AS IDENTITY;\r woodlouse | 2018-04-17 16:42:43 | Check | 2018-04-17 18:54:04.311 CEST [864:6] DETAIL: Failed process was running: ALTER TABLE itest13 ADD COLUMN b int GENERATED BY DEFAULT AS IDENTITY;\r (5 rows) The test case that's failing, in identity.sql, has been there since early February; the lack of any crashes till more recently suggests that something committed in mid-to-late March broke it. I have no idea what's going on there, but I think this is clearly something we need to consider an open item for PG11. I'll put it on the list. regards, tom lane