Glue Visual ETL Data Preview not loading

The issue you're experiencing with AWS Glue Visual ETL data preview not loading for your join node is a known limitation when working with complex operations, especially with Iceberg tables.

Here are some potential causes and solutions:

1. Data Preview Limitations: Data preview in Glue Visual ETL is limited to 200 rows, but complex operations like joins (especially partial joins) can take longer to process even with this limitation. The preview might be timing out before completing.

2. Iceberg Table Complexity: When working with Iceberg tables, there can be additional overhead in processing the metadata and table structure, which can make preview operations slower.

3. Type Mismatches: Sometimes Glue doesn't correctly identify data types during preview operations. This is particularly common when joining tables with potentially mismatched column types. You might have a type mismatch between the join columns that's preventing the preview from completing.

Solutions to try:

1. Check Join Column Data Types: Verify that the columns you're joining on have matching data types. You can check this in the script code and modify if needed.

2. Skip Preview and Run the Job: In some cases, the actual job execution might work fine even if the preview doesn't load. Consider running the job to see if it completes successfully.

3. Check Iceberg Configuration: If you're using Iceberg tables, ensure your Glue job has the proper Iceberg configurations set up for accessing the metadata correctly.

Remember that data preview is primarily a development tool and has limitations, especially with complex operations or large datasets. The actual job execution might still work correctly even if the preview doesn't load.

I hope this helps. If not, then the issue might be specific to your use case. Hence, I suggest you opening a case by reaching out to the specific team and getting your queries resolved.

Sources
AWS Glue Visual ETL Job fails using MERGE statement on Redshift, type mismatch error | AWS re:Post
AWS Glue Interactive Sessions Query Iceberg and Non Iceberg Tables | AWS re:Post