Further review for re-implementation of psql's FETCH_COUNT feature.

Alexander Lakhin noted an obsolete comment, which led me to revisit
some other important comments in the patch, and that study turned up a
couple of unintended ways in which the chunked-fetch code path didn't
match the normal code path in ExecQueryAndProcessResults.  The only
nontrivial problem is that it didn't call PrintQueryStatus, so that
we'd not print the final status result from DML ... RETURNING
commands.  To avoid code duplication, move the filter for whether a
result is from RETURNING from PrintQueryResult to PrintQueryStatus.

Discussion: https://postgr.es/m/0023bea5-79c0-476e-96c8-dad599cc3ad8@gmail.com

Author: tglsfdc

src/bin/psql/common.c

@@ -832,10 +832,7 @@ ExecQueryTuples(const PGresult *result)
 				c;
 
 	/*
-	 * We must turn off gexec_flag to avoid infinite recursion.  Note that
-	 * this allows ExecQueryUsingCursor to be applied to the individual query
-	 * results.  SendQuery prevents it from being applied when fetching the
-	 * queries-to-execute, because it can't handle recursion either.
+	 * We must turn off gexec_flag to avoid infinite recursion.
 	 */
 	pset.gexec_flag = false;
 
@@ -955,30 +952,39 @@ HandleCopyResult(PGresult **resultp, FILE *copystream)
 
 /*
  * PrintQueryStatus: report command status as required
- *
- * Note: Utility function for use by PrintQueryResult() only.
  */
 static void
 PrintQueryStatus(PGresult *result, FILE *printQueryFout)
 {
 	char		buf[16];
+	const char *cmdstatus = PQcmdStatus(result);
 	FILE	   *fout = printQueryFout ? printQueryFout : pset.queryFout;
 
+	/* Do nothing if it's a TUPLES_OK result that isn't from RETURNING */
+	if (PQresultStatus(result) == PGRES_TUPLES_OK)
+	{
+		if (!(strncmp(cmdstatus, "INSERT", 6) == 0 ||
+			  strncmp(cmdstatus, "UPDATE", 6) == 0 ||
+			  strncmp(cmdstatus, "DELETE", 6) == 0 ||
+			  strncmp(cmdstatus, "MERGE", 5) == 0))
+			return;
+	}
+
 	if (!pset.quiet)
 	{
 		if (pset.popt.topt.format == PRINT_HTML)
 		{
 			fputs("<p>", fout);
-			html_escaped_print(PQcmdStatus(result), fout);
+			html_escaped_print(cmdstatus, fout);
 			fputs("</p>\n", fout);
 		}
 		else
-			fprintf(fout, "%s\n", PQcmdStatus(result));
+			fprintf(fout, "%s\n", cmdstatus);
 		fflush(fout);
 	}
 
 	if (pset.logfile)
-		fprintf(pset.logfile, "%s\n", PQcmdStatus(result));
+		fprintf(pset.logfile, "%s\n", cmdstatus);
 
 	snprintf(buf, sizeof(buf), "%u", (unsigned int) PQoidValue(result));
 	SetVariable(pset.vars, "LASTOID", buf);
@@ -988,8 +994,6 @@ PrintQueryStatus(PGresult *result, FILE *printQueryFout)
 /*
  * PrintQueryResult: print out (or store or execute) query result as required
  *
- * Note: Utility function for use by SendQuery() only.
- *
  * last is true if this is the last result of a command string.
  * opt and printQueryFout are defined as for PrintQueryTuples.
  * printStatusFout is where to send command status; NULL means pset.queryFout.
@@ -1002,7 +1006,6 @@ PrintQueryResult(PGresult *result, bool last,
 				 FILE *printStatusFout)
 {
 	bool		success;
-	const char *cmdstatus;
 
 	if (!result)
 		return false;
@@ -1027,14 +1030,7 @@ PrintQueryResult(PGresult *result, bool last,
 			 * status.
 			 */
 			if (last || pset.show_all_results)
-			{
-				cmdstatus = PQcmdStatus(result);
-				if (strncmp(cmdstatus, "INSERT", 6) == 0 ||
-					strncmp(cmdstatus, "UPDATE", 6) == 0 ||
-					strncmp(cmdstatus, "DELETE", 6) == 0 ||
-					strncmp(cmdstatus, "MERGE", 5) == 0)
-					PrintQueryStatus(result, printStatusFout);
-			}
+				PrintQueryStatus(result, printStatusFout);
 
 			break;
 
@@ -1443,6 +1439,9 @@ DescribeQuery(const char *query, double *elapsed_msec)
  * For other commands, the results are processed normally, depending on their
  * status.
  *
+ * When invoked from \watch, is_watch is true and min_rows is the value
+ * of that option, or 0 if it wasn't set.
+ *
  * Returns 1 on complete success, 0 on interrupt and -1 or errors.  Possible
  * failure modes include purely client-side problems; check the transaction
  * status for the server-side opinion.
@@ -1488,11 +1487,21 @@ ExecQueryAndProcessResults(const char *query,
 	}
 
 	/*
-	 * Fetch the result in chunks if FETCH_COUNT is set.  But we don't enable
-	 * chunking if SHOW_ALL_RESULTS is false, since that requires us to
-	 * accumulate all rows before we can tell what should be displayed, which
-	 * would counter the idea of FETCH_COUNT.  Chunking is also disabled when
-	 * \crosstab, \gexec, \gset or \watch is used.
+	 * Fetch the result in chunks if FETCH_COUNT is set, except when:
+	 *
+	 * * SHOW_ALL_RESULTS is false, since that requires us to complete the
+	 * query before we can tell if its results should be displayed.
+	 *
+	 * * We're doing \crosstab, which likewise needs to see all the rows at
+	 * once.
+	 *
+	 * * We're doing \gexec: we must complete the data fetch to make the
+	 * connection free for issuing the resulting commands.
+	 *
+	 * * We're doing \gset: only one result row is allowed anyway.
+	 *
+	 * * We're doing \watch: users probably don't want us to force use of the
+	 * pager for that, plus chunking could break the min_rows check.
 	 */
 	if (pset.fetch_count > 0 && pset.show_all_results &&
 		!pset.crosstab_flag && !pset.gexec_flag &&
@@ -1644,8 +1653,8 @@ ExecQueryAndProcessResults(const char *query,
 		/* If we have a chunked result, collect and print all chunks */
 		if (result_status == PGRES_TUPLES_CHUNK)
 		{
-			FILE	   *tuples_fout = printQueryFout ? printQueryFout : stdout;
-			printQueryOpt my_popt = pset.popt;
+			FILE	   *tuples_fout = printQueryFout ? printQueryFout : pset.queryFout;
+			printQueryOpt my_popt = opt ? *opt : pset.popt;
 			int64		total_tuples = 0;
 			bool		is_pager = false;
 			int			flush_error = 0;
@@ -1670,8 +1679,13 @@ ExecQueryAndProcessResults(const char *query,
 			do
 			{
 				/*
-				 * display the current chunk of results, unless the output
-				 * stream stopped working or we got cancelled
+				 * Display the current chunk of results, unless the output
+				 * stream stopped working or we got cancelled.  We skip use of
+				 * PrintQueryResult and go directly to printQuery, so that we
+				 * can pass the correct is_pager value and because we don't
+				 * want PrintQueryStatus to happen yet.  Above, we rejected
+				 * use of chunking for all cases in which PrintQueryResult
+				 * would send the result to someplace other than printQuery.
 				 */
 				if (success && !flush_error && !cancel_pressed)
 				{
@@ -1710,6 +1724,12 @@ ExecQueryAndProcessResults(const char *query,
 				if (is_pager)
 					ClosePager(tuples_fout);
 
+				/*
+				 * It's possible the data is from a RETURNING clause, in which
+				 * case we need to print query status.
+				 */
+				PrintQueryStatus(result, printQueryFout);
+
 				/*
 				 * We must do a fake SetResultVariables(), since we don't have
 				 * a PGresult corresponding to the whole query.