[Aurora Postgres 17][Bug?] INSERT ON CONFLICT against parent table works, but logs error with invalid ON CONFLICT clause

[Aurora Postgres 17][Bug?] INSERT ON CONFLICT against parent table works, but logs error with invalid ON CONFLICT clause

Instance Family Class: db.t4g
PostgreSQL 17.5 on x86_64-pc-linux-gnu, compiled by x86_64-pc-linux-gnu-gcc (GCC) 10.5.0, 64-bit

Hi there,

I'm facing an buggy error entry in the instance logs when using INSERT ON CONFLICT statement inside a trigger against a partitioned table.

The flow is relatively simple: we stream changes to a table from a subscription, and we have an AFTER TRIGGER FOR EACH ROW to transform the data into another table.

The thing is that the INSERT happens successfully in the background, but the instance logs have several entries with the following error:

2026-04-10 20:36:58 UTC:10.255.170.206(46020):auditlogs_app@auditlogs:[26449]:ERROR:  there is no unique or exclusion constraint matching the ON CONFLICT specification
2026-04-10 20:36:58 UTC:10.255.170.206(46020):auditlogs_app@auditlogs:[26449]:STATEMENT:  
	INSERT INTO audit_logs (
	    producer,
...
		project_id
	) VALUES ( ....)
	ON CONFLICT (producer, local_id) -- ???
	DO NOTHING

The reason I'm thinking is a buggy entry is due to the following:

• I've tested the same scenario locally, with the same Postgres community version, no errors shown.
• The subscription has the disable_on_error = true flag set, so it should stop/disable the subscription activity. However, replication continues working correctly.
• I tested adding a bug in the trigger (which makes the trigger fail), and the subscription gets disabled correctly. That leads me to think that the error in the logs is bugged.
• The expansion in the ON CONFLICT clause, does not match with the function's definition.
• The INSERT happens in the background correctly.

Here are the parts relevant to this case:

CREATE TABLE IF NOT EXISTS audit_logs (
    producer         VARCHAR                     NOT NULL,
    local_id         BIGINT                      NOT NULL,
    created_at       TIMESTAMPTZ                 NOT NULL,
...
    CONSTRAINT audit_logs_pkey PRIMARY KEY (created_at, producer, local_id)
) PARTITION BY RANGE (created_at);

CREATE TABLE IF NOT EXISTS audit_logs_y2025m03 PARTITION OF audit_logs
    FOR VALUES FROM ('2025-03-01 00:00:00+00') TO ('2025-04-01 00:00:00+00');
CREATE UNIQUE INDEX IF NOT EXISTS audit_logs_y2025m03_producer_local_id_uidx ON audit_logs_y2025m03 (producer, local_id);

Trigger definition:

CREATE OR REPLACE FUNCTION insert_into_audit_logs()
RETURNS TRIGGER AS $$
BEGIN
    INSERT INTO public.audit_logs (
        producer,
        local_id,
        environment_id, 
...
        ingested_at
    ) VALUES (
        'producer',                                         -- producer
        NEW.id,                                            -- id
...
        NOW()                                              -- ingested_at
    )
    ON CONFLICT (created_at, producer, local_id) DO NOTHING;
    -- Also tried the following, same error output in the logs:
    --ON CONFLICT ON CONSTRAINT audit_logs_pkey DO NOTHING;

    RETURN NULL;
END;
$$ LANGUAGE plpgsql;

DROP TRIGGER IF EXISTS trigger_insert_into_audit_logs ON origin_table_streamed;

CREATE TRIGGER trigger_insert_into_audit_logs
AFTER INSERT ON origin_table_streamed
FOR EACH ROW
EXECUTE FUNCTION insert_into_audit_logs();

ALTER TABLE origin_table_streamed ENABLE ALWAYS TRIGGER trigger_insert_into_audit_logs;

Cheers,