Thread: [HACKERS] PG_TRY & PG_CATCH in FDW development

I want to share a technical problem that I am facing while writing code for an FDW.
The problem is as follows:
In the FDW call back functions it is recommended to use PG_TRY PG_CATCH blocks along with PG_RE_THROW to disconnect from the foreign server.
I am using the same technique in IterateForeignScan function, and it is supposed to work like this:

 1  PG_TRY();
 2  {
 3  ... code that might throw ereport(ERROR) ...
 4  }
 5  PG_CATCH(); 
 6  {
 7    disconnect_from_foreign_server();
 8    PG_RE_THROW();
 9  }
10  PG_END_TRY();

PG_RE_THROW is supposed to throw the same error again and then take us out of the function.

What is happening for me is that PG_RE_THROW takes me to PG_TRY in the same function and then PG_TRY jumps to PG_CATCH where PG_RE_THROW again jumps to PG_TRY in the same function resulting in an infinite loop. The query therefore never returns. It is supposed to throw the error and quit.My question is what could possibly cause this infinite loop?

--