=========================================== <=== FIRST SESSION
postgres=# begin;
BEGIN
Time: 0.498 ms
postgres=# select * from foo for update;
┌────┐
│ a  │
╞════╡
│ 10 │
└────┘
(1 row)

Time: 1.152 ms
==========================================

****************************************** <=== SECOND SESSION
postgres=# begin;
BEGIN
Time: 0.426 ms
postgres=# select * from foo for update;
******************************************

==========================================
postgres=# select pid, wait_event, state, query from pg_stat_activity ;
┌───────┬───────────────┬────────┬──────────────────────────────────────────────────────────────┐
│  pid  │  wait_event   │ state  │                            query                             │
╞═══════╪═══════════════╪════════╪══════════════════════════════════════════════════════════════╡
│ 22870 │ transactionid │ active │ select * from foo for update;                                │
│ 22874 │ ( null )      │ active │ select pid, wait_event, state, query from pg_stat_activity ; │
└───────┴───────────────┴────────┴──────────────────────────────────────────────────────────────┘
(2 rows)

Time: 1.666 ms --- OOK
=========================================

*****************************************
^CCancel request sent
ERROR:  57014: canceling statement due to user request
CONTEXT:  while locking tuple (0,1) in relation "foo"
LOCATION:  ProcessInterrupts, postgres.c:2977
Time: 121895.558 ms
postgres=# rollback;
ROLLBACK
Time: 0.648 ms
postgres=# begin;
BEGIN
Time: 0.461 ms
postgres=# select * from foo where a = 10 for update;
*****************************************

=========================================
┌───────┬───────────────┬────────┬──────────────────────────────────────────────────────────────┐
│  pid  │  wait_event   │ state  │                            query                             │
╞═══════╪═══════════════╪════════╪══════════════════════════════════════════════════════════════╡
│ 22870 │ transactionid │ active │ select * from foo for update;                                │ <=== expecting select * from foo where a = 10 for update
│ 22874 │ ( null )      │ active │ select pid, wait_event, state, query from pg_stat_activity ; │
└───────┴───────────────┴────────┴──────────────────────────────────────────────────────────────┘
(2 rows)

Time: 1.421 ms
========================================