Could synchronous streaming replication really degrade the performance of the primary?

Hello,

I've heard from some people that synchronous streaming replication has
severe performance impact on the primary. They said that the transaction
throughput of TPC-C like benchmark (perhaps DBT-2) decreased by 50%. I'm
sorry I haven't asked them about their testing environment, because they
just gave me their experience. They think that this result is much worse
than some commercial database.

I'm surprised. I know that the amount of transaction logs of PostgreSQL is
larger than other databases because it it logs the entire row for each
update operation instead of just changed columns, and because of full page
writes. But I can't (and don't want to) believe that those have such big
negative impact.

Does anyone have any experience of benchmarking synchronous streaming
replication under TPC-C or similar write-heavy workload? Could anybody give
me any performance evaluation result if you don't mind?

Regards
MauMau