InnoDB uses a clustered index approach. The primary key index is a B-tree. The actual table data is stored in the leaf nodes of this B-tree. Secondary indexes point to the primary key.

One is not better than the other in general terms. InnoDB's clustered B-tree approach shines when:

You frequently access data in primary key order

Your workload has many range scans on the primary key

You need predictable performance for primary key lookups

Your data naturally has a meaningful ordering that matches your access patterns

PostgreSQL's heap approach excels when:

You frequently update non-key columns (less page splits/reorganization)

You have many secondary indexes (they're smaller without primary keys)

Your access patterns vary widely and don't follow one particular field

You need faster table scans when indexes aren't applicable

I personally find PostgreSQL's approach more flexible for complex analytical workloads with unpredictable access patterns, while InnoDB's clustered approach feels more optimized for OLTP workloads with predictable key-based access patterns. The "better" system depends entirely on your specific workload, data characteristics, and access patterns.

PostgreSQL only has heaps for tables, and various other data structures for indices, with b-tree being the default for indices.

There are many cases where having b-trees for tables would make performance better.

GP is basically poking fun at PG for still having nothing but heaps for tables.