Re: Refactoring postgres_fdw/connection.c

At Tue, 26 Jul 2022 00:54:47 +0900, Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> wrote in
> Hi,
>
> When reviewing the postgres_fdw parallel-abort patch [1], I found that
> there are several duplicate codes in postgres_fdw/connection.c.
> Which seems to make it harder to review the patch changing
> connection.c.
> So I'd like to remove such duplicate codes and refactor the functions
> in connection.c. I attached the following three patches.
>
> There are two functions, pgfdw_get_result() and
> pgfdw_get_cleanup_result(),
> to get a query result. They have almost the same code, call
> PQisBusy(),
> WaitLatchOrSocket(), PQconsumeInput() and PQgetResult() in the loop,
> but only pgfdw_get_cleanup_result() allows its callers to specify the
> timeout.
> 0001 patch transforms pgfdw_get_cleanup_result() to the common
> function
> to get a query result and makes pgfdw_get_result() use it instead of
> its own (duplicate) code. The patch also renames
> pgfdw_get_cleanup_result()
> to pgfdw_get_result_timed().

Agree to that refactoring. And it looks fine to me.

> pgfdw_xact_callback() and pgfdw_subxact_callback() have similar codes
> to
> issue COMMIT or RELEASE SAVEPOINT commands. 0002 patch adds the common
> function,
> pgfdw_exec_pre_commit(), for that purpose, and changes those functions
> so that they use the common one.

I'm not sure the two are similar with each other. The new function
pgfdw_exec_pre_commit() looks like a merger of two isolated code paths
intended to share a seven-line codelet. I feel the code gets a bit
harder to understand after the change. I mildly oppose to this part.

> pgfdw_finish_pre_commit_cleanup() and
> pgfdw_finish_pre_subcommit_cleanup()
> have similar codes to wait for the results of COMMIT or RELEASE
> SAVEPOINT commands.
> 0003 patch adds the common function, pgfdw_finish_pre_commit(), for
> that purpose,
> and replaces those functions with the common one.
> That is, pgfdw_finish_pre_commit_cleanup() and
> pgfdw_finish_pre_subcommit_cleanup()
> are no longer necessary and 0003 patch removes them.

It gives the same feeling with 0002. Considering that
pending_deallocate becomes non-NIL only when toplevel, 38 lines out of
66 lines of the function are the toplevel-dedicated stuff.

> [1] https://commitfest.postgresql.org/38/3392/

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center