RE: [POC] Fast COPY FROM command for the table with foreign partitions

Hi Andrey,

I had a general look at this extension feature, I think it's beneficial for some application scenarios of PostgreSQL. So I did 7 performance cases test on your patch(v13). The results are really good. As you can see below we can get 7-10 times improvement with this patch.

PSA test_copy_from.sql shows my test cases detail(I didn't attach my data file since it's too big).

Below are the test results:
'Test No' corresponds to the number(0 1...6) in attached test_copy_from.sql.
%reg=(Patched-Unpatched)/Unpatched), Unit is millisecond.

|Test No| Test Case |Patched(ms) | Unpatched(ms) |%reg |
|-------|-----------------------------------------------------------------------------------------|-------------|---------------|-------|
|0 |COPY FROM insertion into the partitioned table(parition is foreign table) | 102483.223 | 1083300.907 | -91% |
|1 |COPY FROM insertion into the partitioned table(parition is foreign partition) | 104779.893 | 1207320.287 | -91% |
|2 |COPY FROM insertion into the foreign table(without partition) | 100268.730 | 1077309.158 | -91% |
|3 |COPY FROM insertion into the partitioned table(part of foreign partitions) | 104110.620 | 1134781.855 | -91% |
|4 |COPY FROM insertion into the partitioned table with constraint(part of foreign partition)| 136356.201 | 1238539.603 | -89% |
|5 |COPY FROM insertion into the foreign table with constraint(without partition) | 136818.262 | 1189921.742 | -89% |
|6 |\copy insertion into the partitioned table with constraint. | 140368.072 | 1242689.924 | -89% |

If there is any question on my tests, please feel free to ask.

Best Regard,
Tang