I'm doing some testing so I create some table foo first. And then generate some test data src to do upsert by MERGE. DESC detail foo can see numFiles e.g. 3 when I play around (by MERGE or INSERT), but the files on S3 has more. And I do OPTIMIZE after MERGE or INERT, and not see any changes for files. The parquet files on S3 is from 33KB to 509KB. I expect it can be merged as one file after OPTIMIZE.