Archiving and Restoring Tables That Use Block-Level Compression
Small or highly skewed tables that use block-level compression may be incorrectly archived or restored as not compressed due to random-AMP sampling for block-level compression. If the random-AMP sample checks an AMP without rows for that table, ARC assumes that the table is empty and does not compress it during the archive or restore. If a system has both compressed and uncompressed tables, a DBA needs to be aware of the criteria determining whether a table is compressed and review the uncompressed tables to see whether they are archived and restored correctly.