CockroachDB seems to be a distributed database system written in Go which has implemented a Postgres query/wire protocol compatibility layer.
PolarDB is a Postgres fork actually using the Postgres codebase and extending it to a distributed database system. Maybe one day they can unfork because it's possible to implement PolarDB on top of Postgres as an extension and/or they contribute/get all their changes into Postgres core.
CockroachDB seems to be a distributed database system written in Go which has implemented a Postgres query/wire protocol compatibility layer.
PolarDB is a Postgres fork actually using the Postgres codebase and extending it to a distributed database system. Maybe one day they can unfork because it's possible to implement PolarDB on top of Postgres as an extension and/or they contribute/get all their changes into Postgres core.