PRINT

Synopsis

PRINT topicName [FROM BEGINNING] [INTERVAL interval] [LIMIT limit]

Description

Print the contents of Kafka topics to the ksqlDB CLI.

The topicName is case sensitive. Quote the name if it contains invalid characters. See Valid Identifiers for more information.

The PRINT statement supports the following properties:

Property Description
FROM BEGINNING Print starting with the first message in the topic. If not specified, PRINT starts with the most recent message.
INTERVAL interval Print every interval th message. The default is 1, meaning that every message is printed.
LIMIT limit Stop printing after limit messages. The default value is unlimited, requiring Ctrl+C to terminate the query.

Example

The following statement shows how to print all of the records in a topic named _confluent-ksql-default__command_topic, (the default name for the topic ksqlDB stores your submitted command in). Note, the topic name has been quoted as it contains the invalid dash character.

PRINT '_confluent-ksql-default__command_topic' FROM BEGINNING;

ksqlDB attempts to determine the format of the data in the topic and outputs what it thinks are the key and value formats at the top of the output.

Note

Attempting to determine a data format from only the serialized bytes is not an exact science! For example, it is not possible to distinguish between serialized BIGINT and DOUBLE values, because they both occupy eight bytes. Short strings can also be mistaken for serialized numbers. Where it appears different records are using different formats ksqlDB will state the format is MIXED.

Your output should resemble:

    Key format: JSON or SESSION(KAFKA_STRING) or HOPPING(KAFKA_STRING) or TUMBLING(KAFKA_STRING) or KAFKA_STRING
    Value format: JSON or KAFKA_STRING
    rowtime: 12/21/18 23:58:42 PM PSD, key: stream/CLICKSTREAM/create, value: {statement":"CREATE STREAM clickstream (_time bigint,time varchar, ip varchar, request varchar, status int, userid int, bytes bigint, agent varchar) with (kafka_topic = 'clickstream', value_format = 'json');","streamsProperties":{}}
    rowtime: 12/21/18 23:58:42 PM PSD, key: table/EVENTS_PER_MIN/create, value: {"statement":"create table events_per_min as select userid, count(*) as events from clickstream window  TUMBLING (size 10 second) group by userid EMIT CHANGES;","streamsProperties":{}}
    ^CTopic printing ceased

The key format for this topic is KAFKA_STRING. However, the PRINT command does not know this and has attempted to determine the format of the key by inspecting the data. It has determined that the format may be KAFKA_STRING, but it could also be JSON or a windowed KAFKA_STRING.

The value format for this topic is JSON. However, the PRINT command has also determined it could be KAFKA_STRING. This is because JSON is serialized as text. Hence you could choose to deserialize this value data as a KAFKA_STRING if you wanted to. However, JSON is likely the better option.

Page last revised on: 2020-02-14


Last update: 2020-02-14