Deleting rows in an HDFS-backed table does not immediately reduce file size because HDFS is immutable by design and individual records cannot be removed in place.
In Hive ACID tables, a DELETE does not touch the base data files at all. Instead, it writes a separate delete delta file that marks rows as logically deleted using row ID references. The physical file size on HDFS stays the same or increases because new delta files are being added. Actual size reduction only happens after a major compaction runs, which rewrites the base files by merging all deltas and physically excluding deleted rows, followed by the HDFS cleaner removing the old files.
In Apache Iceberg, deletes produce position or equality delete files written alongside existing data files, again increasing HDFS usage until a rewrite data files compaction purges the old data. In Apache Hudi Copy-On-Write, a DELETE rewrites the entire affected file immediately so size does reduce, but with heavy write amplification. In Merge-On-Read, deletes are appended as log files and compaction is still required for physical reclamation.
The bottom line is that DELETE is always append-driven at the HDFS storage layer regardless of table format, and true physical space reclamation requires compaction to run and obsolete files to be purged.
