STREAM LEFT JOIN TABLE drops a subset of events (rows not emitted)

[Sh4dow998]

Environment

• ksqlDB: 0.29.0 (confluentinc/ksqldb-server:0.29.0, confluentinc/ksqldb-cli:0.29.0)
• Kafka: Confluent Platform 7.9.1 (cp-kafka:7.9.1, cp-zookeeper:7.9.1)
• Kafka Connect: debezium/connect:2.7.3.Final (MariaDB)
• Deployment: Docker, bridge network
• Serdes: KEY_FORMAT='KAFKA', VALUE_FORMAT='JSON'
• All topics in this repro: PARTITIONS=1

Context

We enrich an event stream with:

• a TABLE mapping event_type (INT) to a label (STRING),
• a TABLE mapping device_type (INT) to a label (STRING),
• two dimension TABLEs for users and organizations (join on uuid).

With the TABLE join on event_type, some events never appear in the output stream at all. There are no NULL labels; the rows are simply not emitted. If we replace the TABLE join with either a CASE mapping, all events are emitted as expected.

Minimal reproduction

Session settings:

SET 'auto.offset.reset'='earliest';
SET 'ksql.streams.cache.max.bytes.buffering'='0';

Mapping TABLE:

CREATE TABLE EVENT_TYPE_MAP (
  event_type INT PRIMARY KEY,
  event_type_label VARCHAR
) WITH (
  KAFKA_TOPIC='vw_event_type_map',
  KEY_FORMAT='KAFKA',
  VALUE_FORMAT='JSON',
  PARTITIONS=1
);

INSERT INTO EVENT_TYPE_MAP VALUES (1000, 'UserLoggedIn');
INSERT INTO EVENT_TYPE_MAP VALUES (1100, 'CipherCreated');

Source STREAM and two events

CREATE STREAM VW_EVENT (
  uuid STRING KEY,
  event_type INT
) WITH (
  KAFKA_TOPIC='vw_event',
  KEY_FORMAT='KAFKA',
  VALUE_FORMAT='JSON',
  PARTITIONS=1
);

Enriched output with LEFT JOIN (problematic path):

CREATE STREAM VW_EVENT_ENRICHED WITH (
  KAFKA_TOPIC='vw_enriched',
  VALUE_FORMAT='JSON'
) AS
SELECT
  ev.uuid,
  ev.event_type,
  m.event_type_label
FROM VW_EVENT ev
LEFT JOIN EVENT_TYPE_MAP m
  ON ev.event_type = m.event_type
EMIT CHANGES;

Observation:

SELECT uuid, event_type, event_type_label
FROM VW_EVENT_ENRICHED
EMIT CHANGES LIMIT 2;

Actual: only one of the two input events appears in vw_enriched (the 1000 case). The 1100 event is not emitted at all.
Expected: both rows should be emitted (1000 → 'UserLoggedIn', 1100 → 'CipherCreated').

• Troubleshooting already done
• Ensured only one query writes to the output (SHOW QUERIES).
• Dropped and recreated all objects and topics (TERMINATE, DROP ... DELETE TOPIC).
• Set auto.offset.reset='earliest' before creating objects.
• Verified the mapping TABLE is populated:
  • PRINT 'vw_event_type_map' FROM BEGINNING shows the inserted rows.
  • SELECT * FROM EVENT_TYPE_MAP EMIT CHANGES LIMIT 2; returns the rows.
• Tried explicit casts in the join (CAST(ev.event_type AS INT) = CAST(m.event_type AS INT)).
• No WHERE clause filtering the result.
• The same pattern with TABLE joins on uuid STRING for users/orgs works correctly; the problem seems specific to the INT mapping TABLE join.

Question

Could you help explain why a STREAM LEFT JOIN TABLE on an INT column would drop some rows (no emission) even though matching entries exist in the TABLE, and how to resolve this?