PostgreSQL crashes during count row query Currently I have only two tables - small one that works fine and another presumably large one.
When I try to find out row count in pgAdmin I get the following error:

The application has lost the database connection:
⁃ If the connection was idle it may have been forcibly disconnected.
⁃ The application server or database server may have been restarted.
⁃ The user session may have timed out.
Do you want to continue and establish a new session?


I also checked the Postgres server logs:

2020-03-30 03:06:06.764 MSK [37356] LOG:  server process (PID 30712) was terminated by signal 9: Killed: 9
2020-03-30 03:06:06.764 MSK [37356] DETAIL:  Failed process was running: SELECT COUNT(*)::text FROM ios.task_info;
2020-03-30 03:06:06.764 MSK [37356] LOG:  terminating any other active server processes
2020-03-30 03:06:06.765 MSK [30810] WARNING:  terminating connection because of crash of another server process
2020-03-30 03:06:06.765 MSK [30810] DETAIL:  The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.
2020-03-30 03:06:06.765 MSK [30810] HINT:  In a moment you should be able to reconnect to the database and repeat your command.
2020-03-30 03:06:06.765 MSK [30709] WARNING:  terminating connection because of crash of another server process
2020-03-30 03:06:06.765 MSK [30709] DETAIL:  The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.
2020-03-30 03:06:06.765 MSK [30709] HINT:  In a moment you should be able to reconnect to the database and repeat your command.
2020-03-30 03:06:06.767 MSK [37356] LOG:  all server processes terminated; reinitializing
2020-03-30 03:06:06.776 MSK [30816] LOG:  database system was interrupted; last known up at 2020-03-30 02:51:14 MSK
2020-03-30 03:06:06.818 MSK [30817] FATAL:  the database system is in recovery mode
2020-03-30 03:06:06.853 MSK [30816] LOG:  database system was not properly shut down; automatic recovery in progress
2020-03-30 03:06:06.855 MSK [30816] LOG:  redo starts at 0/4F4DE850
2020-03-30 03:06:06.855 MSK [30816] LOG:  invalid record length at 0/4F4DE888: wanted 24, got 0
2020-03-30 03:06:06.855 MSK [30816] LOG:  redo done at 0/4F4DE850
2020-03-30 03:06:06.862 MSK [37356] LOG:  database system is ready to accept connections


I run everything on my OS X Catalina laptop and use PostgreSQL 12 EnterpriseDB.

Just in case if it is important - I created the large table sending several large CSV COPY queries in my Python script. 
What can be the reason of these errors?
I run everything on my OS X Catalina laptop and use PostgreSQL 12
  EnterpriseDB.


There is a JIT-related problem on this platform and version that leads to the kind of crash you're reporting. It's explained on mailing lists:

Re: PG v12.2 - Setting jit_above_cost is causing the server to crash

At the moment, the workaround seeems to be to set jit = off until EDB releases a new version with a fix, hopefully in PostgreSQL 12.3