INSERT rule does not always fire - postgresql

Question

We have a Postgres 11 server. There is table of machines and history table which contains the changes within machines table.
There is insert rule on machines table:
CREATE RULE machine_insert AS ON INSERT TO machines
DO ALSO
INSERT INTO history(machine_name, stamp, ...)
VALUES(new.machine_name, now(), ...);
The insert into history works perfectly if the statement looks like this
INSERT INTO machines(machine_name, ....)
SELECT machine_name from new_machines; -- No condition
But if there is a JOIN and WHERE condition in the select statement, the rule does not fire at all. e.g.
INSERT INTO machines(machine_name, ....)
SELECT machine_name
FROM new_machines N
LEFT OUTER JOIN machines D on D.machine_name = N.machine_name
WHERE D.machine_name is null -- "Anti Join"
As I understand the documentation, the select statement in my case above should really have no impact on the rule(s). Remark: simple WHERE condition (WHERE machine_type is not null) does not disable the rule. What am I doing wrong?

Answer 1

The EXPLAIN ANALYZE revealed the cause of the issue. Here is the output:
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------------
Insert on machines (cost=17.88..14522.89 rows=335609 width=227) (actual time=12586.221..12586.223 rows=0 loops=1)
-> Hash Anti Join (cost=17.88..14522.89 rows=335609 width=227) (actual time=0.029..347.021 rows=335959 loops=1)
Hash Cond: (n.machine_name = d.machine_name)
-> Seq Scan on new_machines n (cost=0.00..8588.59 rows=335959 width=105) (actual time=0.013..59.920 rows=335959 loops=1)
-> Hash (cost=13.50..13.50 rows=350 width=4) (actual time=0.002..0.003 rows=0 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 8kB
-> Seq Scan on machines d (cost=0.00..13.50 rows=350 width=4) (actual time=0.002..0.002 rows=0 loops=1)
Planning Time: 1.497 ms
Execution Time: 12586.289 ms
Insert on history (cost=0.84..30581.85 rows=121724 width=1493) (actual time=212.911..212.912 rows=0 loops=1)
-> Merge Anti Join (cost=0.84..30581.85 rows=121724 width=1493) (actual time=212.909..212.909 rows=0 loops=1)
Merge Cond: (n.machine_name = d.machine_name)
-> Index Scan using new_machines_idx on new_machines n (cost=0.42..12138.50 rows=335959 width=15) (actual time=0.005..72.153
-> Index Only Scan using machines_id_key on machines d (cost=0.42..11274.51 rows=214235 width=4) (actual time=0.005..81.540 rows=335959 loops=1)
Heap Fetches: 335959
Planning Time: 0.264 ms
Execution Time: 212.975 ms
The rule does fire (gets executed) and it does work as designed.
The query resulting from the RULE (see Insert on history above) really tries to add records to history, but under the WHERE condition that the record must not exist in machines table which is now FALSE for all records as INSERT into machines already went through, note Scan using machines_id_key ... rows=335959.