SAP HANA
What it is
SAP's in-memory, columnar database and the foundation of S/4HANA. Its speed for set-based and analytical queries is what makes code-pushdown (CDS, AMDP) the right pattern.
Why it matters for Clean Core
HANA changes the performance contract: the operations that were cheap on a row store (and the loops that hid them) are now the wrong shape. Cloud-clean code is also code written for HANA's strengths.
Common pitfall
Carrying classic 'pull rows, loop in ABAP' habits onto HANA. The database can do the aggregation/join far faster — and CDS is how you ask it to. The move to S/4HANA is also a move to set-based thinking.