Best practices for Iceberg in Cloudera

Based on large scale TPC-DS benchmark testing, performance testing and real-world experiences, Cloudera recommends several best practices when using Iceberg.

Follow the best practices listed below when using Iceberg:

• Use Iceberg as intended for analytics.

  The table format is designed to manage a large, slow-changing collection of files. For more information, see the Iceberg spec.

• Increase parallelism to handle large manifest list files in Spark.

  By default, the number of processors determines the preset value of the iceberg.worker.num-threads system property. Try increasing parallelism by setting the iceberg.worker.num-threads system property to a higher value to speed up query compilation.

• Reduce read amplification

  Monitor the growth of positional delta files, and perform timely compactions.

• Speed up drop table performance, preventing deletion of data files by using the following table properties:

  Set external.table.purge=false and gc.enabled=false

• Tune the following table properties to improve concurrency on writes and reduce commit failures: commit.retry.num-retries (default is 4), commit.retry.min-wait-ms (default is 100)
• Maintain a relatively small number of data files under the iceberg table/partition directory for efficient reads. To alleviate poor performance caused by too many small files, run the following queries:

  TRUNCATE TABLE target;
                INSERT OVERWRITE TABLE target select * from target FOR SYSTEM_VERSION AS OF <preTruncateSnapshotId>; 

• To minimize the number of delete files and file handles and improve performance, ensure that the Spark write.distribution.mode table property value is “hash” (the default setting for Spark Iceberg 1.2.0 onwards).