PostgreSQL lock simulator
Create environment where everyone can test how to resolve PostgreSQL lock issue.
- requirements: docker, Unix(Linux or Mac), bash
Start: Download file ./lockTutorial.sh and run(. ./lockTutorial.sh).
How to find who on local system take lock
postgres=# SELECT client_addr,client_port FROM pg_stat_activity WHERE pid = 5232;
client_addr | client_port
-------------+-------------
127.0.0.1 | 56586
root@db01 ~ # netstat -ntp | grep 56586
tcp 0 0 127.0.0.1:5432 127.0.0.1:56586 ESTABLISHED 5232/postgres: postgres postgres 1
tcp 0 0 127.0.0.1:56586 127.0.0.1:5432 ESTABLISHED 37244/1
root@db0 ~ # cat /proc/37244/cmdline
sshd: ondrej.prochazka@pts/1
How to stop query and release locks
We’ll use the pids we found from the earlier queries:
design_system=> SELECT pg_cancel_backend(11929);
pg_cancel_backend
-------------------
t
(1 row)
This feedback, unfortunately neither accurately indicates success or failure. Instead, you’ll likely have to check locks by previous queries to determine if the process is still active.
That was the nice way to ask (ie, pg_cancel_backend). The more forceful method is:
design_system=> SELECT pg_terminate_backend(11929);
pg_terminate_backend
----------------------
t
(1 row)
!!! Warning: pg_terminate_backend will stop all postgres process and be reason for recovery mode with rollback to last savepoint.