RisingWave supports merge-on-read (MoR) mode as the default write mode for Iceberg tables and sinks. In this mode, both data files and delete files are written directly into the tables and sinks. When external queries are executed, the engine reads these files and merges them to produce the latest view of the data.

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Scenario

This mode is particularly efficient for continuous ingestion because it avoids rewriting data files for every update or delete. However, queries must apply delete files at read time, which can add overhead. Merge-on-read is ideal when downstream systems, such as query engines, natively support Iceberg deletes and can efficiently reconstruct the latest data.

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Example

To use Merge-on-Read mode, set the parameter write_mode = 'merge-on-read' when creating your Iceberg table or sink.
Create an Iceberg engine table
CREATE TABLE t_merge_on_read (
    id INT PRIMARY KEY,
    value STRING
) WITH (
    write_mode = 'merge-on-read'
) ENGINE = iceberg;
Create an Iceberg sink
CREATE SINK rest_sink FROM my_data
WITH (
    connector = 'iceberg',
    type = 'upsert',
    primary_key = 'id',
    warehouse.path = 's3://my-bucket/warehouse',
    database.name = 'my_database',
    table.name = 'my_table',
    catalog.type = 'rest',
    catalog.uri = 'http://rest-catalog:8181',
    catalog.credential = 'username:password',
    s3.access.key = 'your-access-key',
    s3.secret.key = 'your-secret-key',
    enable_compaction = true,
    write_mode = 'merge-on-read',
    commit_checkpoint_interval = 10,
    compaction_interval_sec = 30,
    enable_snapshot_expiration = true,
    snapshot_expiration_max_age_millis=0
);