When tables use Exadata Hybrid Columnar Compression, Oracle DML locks larger blocks of data (compression unit) which might reduce concurrency
a. For basic and online archival compression inserted and updated rows are uncompressed
b. Higher compression levels of Exadata Hybrid Columnar Compression are achieved only with data that is direct-path inserted
c. High CPU overhead in case Warehouse compression
d. Conventional inserts and updates are supported in Exadata Hybrid Columnar Compression but the extent of compression is low