BUG #16184: Segmentation Fault during update

The following bug has been logged on the website:

Bug reference:      16184
Logged by:          Piotr Wlodarczyk
Email address:      piotrwlodarczyk89@gmail.com
PostgreSQL version: 12.1
Operating system:   Linux dev-g1-db-synchro.gnb.adm 3.10.0-1062.7.1.el
Description:

Hello geeks,

We're preparing to upgrade postgresql from 11.5 to 12.1 but still we have
some bugs and issues. Most of them are our fault, but now we have problem we
don't know how to play with it.

Log:
2020-01-02 15:42:26 CET [12729]: [95-1] user=,db=,xid=0,state=00000 LOG:
server process (PID 28879) was terminated by signal 11: Segmentation fault
2020-01-02 15:42:26 CET [12729]: [96-1] user=,db=,xid=0,state=00000 DETAIL:
Failed process was running: UPDATE job_abstract a
          SET job_status = job_status
          WHERE (a.xmax :: TEXT :: BIGINT < (SELECT

txid_snapshot_xmin(txid_current_snapshot()))) AND ((SELECT

                        txid_snapshot_xmin(

                            txid_current_snapshot())

                        <= (SELECT

                              txid_snapshot_xmax(

                                  txid_current_snapshot()))))
                AND job_status = 0 AND NOT xmax = 0;

Please don't ask me why this update is made in this way - I suppose to set
xmax to 0 but why? I don't know. Its legacy code, being part of core of our
application.

Reproducting this bug is not easy and I don't know which conditions has to
be met to replicate this bug. But during application is working and we made
this update, segmentation fault occurs. But sometimes it works. 

Column job_status is telling application that this row should be preceded
one more time. Up to 11.5 this bug doesn't exists.