Recent failures in IsolationCheck deadlock-hard

Hi,

There have been five failures on three animals like this, over the
past couple of months:

 step s6a7: LOCK TABLE a7; <waiting ...>
 step s7a8: LOCK TABLE a8; <waiting ...>
 step s8a1: LOCK TABLE a1; <waiting ...>
-step s8a1: <... completed>
 step s7a8: <... completed>
-error in steps s8a1 s7a8: ERROR:  deadlock detected
+step s8a1: <... completed>
+ERROR:  deadlock detected
 step s8c: COMMIT;
 step s7c: COMMIT;
 step s6a7: <... completed>

 https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=anole&dt=2019-07-18%2021:57:59
 https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=gharial&dt=2019-07-10%2005:59:16
 https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=hyrax&dt=2019-07-08%2015:02:17
 https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=gharial&dt=2019-06-23%2004:17:09
 https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=gharial&dt=2019-06-12%2021:46:24

Before that there were some like that a couple of years back:

 https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=hyrax&dt=2017-04-09%2021:58:03
 https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=hyrax&dt=2017-04-08%2021:58:04
 https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=hyrax&dt=2017-04-08%2005:19:17
 https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=hyrax&dt=2017-04-07%2000:23:39
 https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=hyrax&dt=2017-04-05%2018:58:04

-- 
Thomas Munro
https://enterprisedb.com