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From: Tom Lane <[email protected]>
To: Daniel Verite <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: Jakub Wartak <[email protected]>
Subject: Re: psql's FETCH_COUNT (cursor) is not being respected for CTEs
Date: Fri, 24 Mar 2023 16:12:58 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

"Daniel Verite" <[email protected]> writes:
> PFA an updated patch.

This gives me several "-Wincompatible-pointer-types" warnings
(as are also reported by the cfbot):

common.c: In function 'ExecQueryAndProcessResults':
common.c:1686:24: warning: passing argument 1 of 'PrintQueryTuples' from incompatible pointer type [-Wincompatible-pointer-types]
       PrintQueryTuples(result_array, ntuples, &my_popt, tuples_fout);
                        ^~~~~~~~~~~~
common.c:679:35: note: expected 'const PGresult **' {aka 'const struct pg_result **'} but argument is of type 'PGresult **' {aka 'struct pg_result **'}
 PrintQueryTuples(const PGresult **result, int nresults, const printQueryOpt *opt,
                  ~~~~~~~~~~~~~~~~~^~~~~~
common.c:1720:24: warning: passing argument 1 of 'PrintQueryTuples' from incompatible pointer type [-Wincompatible-pointer-types]
       PrintQueryTuples(result_array, ntuples, &my_popt, tuples_fout);
                        ^~~~~~~~~~~~
common.c:679:35: note: expected 'const PGresult **' {aka 'const struct pg_result **'} but argument is of type 'PGresult **' {aka 'struct pg_result **'}
 PrintQueryTuples(const PGresult **result, int nresults, const printQueryOpt *opt,
                  ~~~~~~~~~~~~~~~~~^~~~~~

I think the cause is the inconsistency about whether PGresult pointers
are pointer-to-const or not.  Even without compiler warnings, I find
code like this very ugly:

-				success = PrintQueryTuples(result, opt, printQueryFout);
+				success = PrintQueryTuples((const PGresult**)&result, 1, opt, printQueryFout);

I think what you probably ought to do to avoid all that is to change
the arguments of PrintQueryResult and nearby routines to be "const
PGresult *result" not just "PGresult *result".

I find it sad that we can't get rid of ExecQueryUsingCursor().
Maybe a little effort towards reducing overhead in the single-row
mode would help?

			regards, tom lane

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