Thread

Re: COPY ON_CONFLICT TABLE; save duplicated record to another table.

Zsolt Parragi <zsolt.parragi@percona.com> — 2026-05-06T22:17:35Z

Hello!

I tried the patch and found a few issues.

1. Two of them are null pointer dereference crashes, one with
partitioned tables:

CREATE TABLE part_t (a int PRIMARY KEY, b text) PARTITION BY RANGE (a);
CREATE TABLE part_t_p1 PARTITION OF part_t FOR VALUES FROM (0) TO (1000);
CREATE TABLE conflict_log (
    rel        oid,
    file_name  text,
    line_no    bigint,
    raw_line   text
);

INSERT INTO part_t VALUES (1, 'pre-existing');
COPY part_t (a, b) FROM stdin WITH (on_conflict 'table',
conflict_table 'conflict_log');
2 row-two
1 dup
3 row-three
\.


2. And another with repeateable reads:

CREATE TABLE t_rr (a int PRIMARY KEY, b text);
CREATE TABLE conflict_log (rel oid, fname text, ln bigint, raw text);
INSERT INTO t_rr VALUES (1, 'pre-committed');

BEGIN ISOLATION LEVEL REPEATABLE READ;
COPY t_rr FROM stdin WITH (on_conflict 'table', conflict_table 'conflict_log');
1 dup-row
\.


3. There's also a possible data loss scenario, reports 3 copied 0 actual:

CREATE TABLE conf_log (
    relname     oid,
    fname       text,
    lineno      bigint,
    rawline     text
);

CREATE TABLE no_idx_tgt (id int, payload text);

CREATE FUNCTION noop_trig() RETURNS trigger LANGUAGE plpgsql AS $$
BEGIN
    RETURN NEW;
END;
$$;

CREATE TRIGGER noop_before BEFORE INSERT ON no_idx_tgt
    FOR EACH ROW EXECUTE FUNCTION noop_trig();

COPY no_idx_tgt (id, payload) FROM STDIN
    WITH (ON_CONFLICT TABLE, CONFLICT_TABLE conf_log);
1 alpha
2 beta
3 gamma
\.

SELECT 'A: no_idx_tgt count' AS scenario, count(*) AS rows FROM no_idx_tgt;
SELECT 'A: conf_log count'  AS scenario, count(*) AS rows FROM conf_log;
SELECT * FROM no_idx_tgt ORDER BY id;


4. Shouldn't the following error out?

CREATE TABLE t (a int PRIMARY KEY, b text);
COPY t TO '/dev/null' (ON_CONFLICT TABLE, CONFLICT_TABLE no_such_table);