RE: Idea to enhance pgbench by more modes to generate data (multi-TXNs, UNNEST, COPY BINARY)

Hi Boris,

I've finished reviewing the latest v15 version of your patch, everything looks good.
- The patch is applied to the current version of the master branch.
- All check-world tests pass. The patch adds tests for the implemented functionality.
- The code conforms to the PostgreSQL coding style (verified by pgindent).
- The added functionality has been tested and works as expected.
- The added functionality does not violate the existing one.
- Difficult-to-understand code locations are properly commented.
- The documentation has been updated and is correct.

The patch adds two additional data generation modes to pgbench: SELECT unnest on the
server and COPY.. FROM BINARY on the client. As well as a setting that includes
adding data in multitransaction mode. This allows you to positively influence
performance at large --scale=. All this will also make it possible to implement
parallel data loading in several sessions in the future.
The unnest mode will be useful for columnar tables.

All of the above allows me to consider the patch ready for the committer.

I am updating the patch to the Ready for Committer status.

Best regards,
Egor