Add libpq pipeline mode support to pgbench

New metacommands \startpipeline and \endpipeline allow the user to run
queries in libpq pipeline mode.

Author: Daniel Vérité <daniel@manitou-mail.org>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/b4e34135-2bd9-4b8a-94ca-27d760da26d7@manitou-mail.org

doc/src/sgml/ref/pgbench.sgml

@@ -1110,6 +1110,12 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
       row, the last value is kept.
      </para>
 
+     <para>
+      <literal>\gset</literal> and <literal>\aset</literal> cannot be used in
+      pipeline mode, since the query results are not yet available by the time
+      the commands would need them.
+     </para>
+
      <para>
       The following example puts the final account balance from the first query
       into variable <replaceable>abalance</replaceable>, and fills variables
@@ -1270,6 +1276,22 @@ SELECT 4 AS four \; SELECT 5 AS five \aset
 </programlisting></para>
     </listitem>
    </varlistentry>
+
+   <varlistentry id='pgbench-metacommand-pipeline'>
+    <term><literal>\startpipeline</literal></term>
+    <term><literal>\endpipeline</literal></term>
+
+    <listitem>
+      <para>
+        These commands delimit the start and end of a pipeline of SQL
+        statements.  In pipeline mode, statements are sent to the server
+        without waiting for the results of previous statements.  See
+        <xref linkend="libpq-pipeline-mode"/> for more details.
+        Pipeline mode requires the use of extended query protocol.
+     </para>
+    </listitem>
+   </varlistentry>
+
   </variablelist>
  </refsect2>
 

src/bin/pgbench/pgbench.c

@@ -395,10 +395,11 @@ typedef enum
 	 *
 	 * CSTATE_START_COMMAND starts the execution of a command.  On a SQL
 	 * command, the command is sent to the server, and we move to
-	 * CSTATE_WAIT_RESULT state.  On a \sleep meta-command, the timer is set,
+	 * CSTATE_WAIT_RESULT state unless in pipeline mode. On a \sleep
-	 * and we enter the CSTATE_SLEEP state to wait for it to expire. Other
+	 * meta-command, the timer is set, and we enter the CSTATE_SLEEP state to
-	 * meta-commands are executed immediately.  If the command about to start
+	 * wait for it to expire. Other meta-commands are executed immediately. If
-	 * is actually beyond the end of the script, advance to CSTATE_END_TX.
+	 * the command about to start is actually beyond the end of the script,
+	 * advance to CSTATE_END_TX.
 	 *
 	 * CSTATE_WAIT_RESULT waits until we get a result set back from the server
 	 * for the current command.
@@ -530,7 +531,9 @@ typedef enum MetaCommand
 	META_IF,					/* \if */
 	META_ELIF,					/* \elif */
 	META_ELSE,					/* \else */
-	META_ENDIF					/* \endif */
+	META_ENDIF,					/* \endif */
+	META_STARTPIPELINE,			/* \startpipeline */
+	META_ENDPIPELINE			/* \endpipeline */
 } MetaCommand;
 
 typedef enum QueryMode
@@ -2568,6 +2571,10 @@ getMetaCommand(const char *cmd)
 		mc = META_GSET;
 	else if (pg_strcasecmp(cmd, "aset") == 0)
 		mc = META_ASET;
+	else if (pg_strcasecmp(cmd, "startpipeline") == 0)
+		mc = META_STARTPIPELINE;
+	else if (pg_strcasecmp(cmd, "endpipeline") == 0)
+		mc = META_ENDPIPELINE;
 	else
 		mc = META_NONE;
 	return mc;
@@ -2757,12 +2764,26 @@ sendCommand(CState *st, Command *command)
 				if (commands[j]->type != SQL_COMMAND)
 					continue;
 				preparedStatementName(name, st->use_file, j);
+				if (PQpipelineStatus(st->con) == PQ_PIPELINE_OFF)
+				{
 					res = PQprepare(st->con, name,
 									commands[j]->argv[0], commands[j]->argc - 1, NULL);
 					if (PQresultStatus(res) != PGRES_COMMAND_OK)
 						pg_log_error("%s", PQerrorMessage(st->con));
 					PQclear(res);
 				}
+				else
+				{
+					/*
+					 * In pipeline mode, we use asynchronous functions. If a
+					 * server-side error occurs, it will be processed later
+					 * among the other results.
+					 */
+					if (!PQsendPrepare(st->con, name,
+									   commands[j]->argv[0], commands[j]->argc - 1, NULL))
+						pg_log_error("%s", PQerrorMessage(st->con));
+				}
+			}
 			st->prepared[st->use_file] = true;
 		}
 
@@ -2802,10 +2823,11 @@ readCommandResponse(CState *st, MetaCommand meta, char *varprefix)
 	int			qrynum = 0;
 
 	/*
-	 * varprefix should be set only with \gset or \aset, and SQL commands do
+	 * varprefix should be set only with \gset or \aset, and \endpipeline and
-	 * not need it.
+	 * SQL commands do not need it.
 	 */
 	Assert((meta == META_NONE && varprefix == NULL) ||
+		   ((meta == META_ENDPIPELINE) && varprefix == NULL) ||
 		   ((meta == META_GSET || meta == META_ASET) && varprefix != NULL));
 
 	res = PQgetResult(st->con);
@@ -2874,6 +2896,13 @@ readCommandResponse(CState *st, MetaCommand meta, char *varprefix)
 				/* otherwise the result is simply thrown away by PQclear below */
 				break;
 
+			case PGRES_PIPELINE_SYNC:
+				pg_log_debug("client %d pipeline ending", st->id);
+				if (PQexitPipelineMode(st->con) != 1)
+					pg_log_error("client %d failed to exit pipeline mode: %s", st->id,
+								 PQerrorMessage(st->con));
+				break;
+
 			default:
 				/* anything else is unexpected */
 				pg_log_error("client %d script %d aborted in command %d query %d: %s",
@@ -3127,13 +3156,36 @@ advanceConnectionState(TState *thread, CState *st, StatsData *agg)
 				/* Execute the command */
 				if (command->type == SQL_COMMAND)
 				{
+					/* disallow \aset and \gset in pipeline mode */
+					if (PQpipelineStatus(st->con) != PQ_PIPELINE_OFF)
+					{
+						if (command->meta == META_GSET)
+						{
+							commandFailed(st, "gset", "\\gset is not allowed in pipeline mode");
+							st->state = CSTATE_ABORTED;
+							break;
+						}
+						else if (command->meta == META_ASET)
+						{
+							commandFailed(st, "aset", "\\aset is not allowed in pipeline mode");
+							st->state = CSTATE_ABORTED;
+							break;
+						}
+					}
+
 					if (!sendCommand(st, command))
 					{
 						commandFailed(st, "SQL", "SQL command send failed");
 						st->state = CSTATE_ABORTED;
 					}
 					else
+					{
+						/* Wait for results, unless in pipeline mode */
+						if (PQpipelineStatus(st->con) == PQ_PIPELINE_OFF)
 							st->state = CSTATE_WAIT_RESULT;
+						else
+							st->state = CSTATE_END_COMMAND;
+					}
 				}
 				else if (command->type == META_COMMAND)
 				{
@@ -3273,7 +3325,15 @@ advanceConnectionState(TState *thread, CState *st, StatsData *agg)
 				if (readCommandResponse(st,
 										sql_script[st->use_file].commands[st->command]->meta,
 										sql_script[st->use_file].commands[st->command]->varprefix))
+				{
+					/*
+					 * outside of pipeline mode: stop reading results.
+					 * pipeline mode: continue reading results until an
+					 * end-of-pipeline response.
+					 */
+					if (PQpipelineStatus(st->con) != PQ_PIPELINE_ON)
 						st->state = CSTATE_END_COMMAND;
+				}
 				else
 					st->state = CSTATE_ABORTED;
 				break;
@@ -3516,6 +3576,45 @@ executeMetaCommand(CState *st, pg_time_usec_t *now)
 			return CSTATE_ABORTED;
 		}
 	}
+	else if (command->meta == META_STARTPIPELINE)
+	{
+		/*
+		 * In pipeline mode, we use a workflow based on libpq pipeline
+		 * functions.
+		 */
+		if (querymode == QUERY_SIMPLE)
+		{
+			commandFailed(st, "startpipeline", "cannot use pipeline mode with the simple query protocol");
+			return CSTATE_ABORTED;
+		}
+
+		if (PQpipelineStatus(st->con) != PQ_PIPELINE_OFF)
+		{
+			commandFailed(st, "startpipeline", "already in pipeline mode");
+			return CSTATE_ABORTED;
+		}
+		if (PQenterPipelineMode(st->con) == 0)
+		{
+			commandFailed(st, "startpipeline", "failed to enter pipeline mode");
+			return CSTATE_ABORTED;
+		}
+	}
+	else if (command->meta == META_ENDPIPELINE)
+	{
+		if (PQpipelineStatus(st->con) != PQ_PIPELINE_ON)
+		{
+			commandFailed(st, "endpipeline", "not in pipeline mode");
+			return CSTATE_ABORTED;
+		}
+		if (!PQpipelineSync(st->con))
+		{
+			commandFailed(st, "endpipeline", "failed to send a pipeline sync");
+			return CSTATE_ABORTED;
+		}
+		/* Now wait for the PGRES_PIPELINE_SYNC and exit pipeline mode there */
+		/* collect pending results before getting out of pipeline mode */
+		return CSTATE_WAIT_RESULT;
+	}
 
 	/*
 	 * executing the expression or shell command might have taken a
@@ -4725,7 +4824,9 @@ process_backslash_command(PsqlScanState sstate, const char *source)
 			syntax_error(source, lineno, my_command->first_line, my_command->argv[0],
 						 "missing command", NULL, -1);
 	}
-	else if (my_command->meta == META_ELSE || my_command->meta == META_ENDIF)
+	else if (my_command->meta == META_ELSE || my_command->meta == META_ENDIF ||
+			 my_command->meta == META_STARTPIPELINE ||
+			 my_command->meta == META_ENDPIPELINE)
 	{
 		if (my_command->argc != 1)
 			syntax_error(source, lineno, my_command->first_line, my_command->argv[0],

src/bin/pgbench/t/001_pgbench_with_server.pl

@@ -41,7 +41,7 @@ sub pgbench
 			# filenames are expected to be unique on a test
 			if (-e $filename)
 			{
-				ok(0, "$filename must not already exists");
+				ok(0, "$filename must not already exist");
 				unlink $filename or die "cannot unlink $filename: $!";
 			}
 			append_to_file($filename, $$files{$fn});
@@ -755,6 +755,83 @@ pgbench(
 }
 	});
 
+# Working \startpipeline
+pgbench(
+	'-t 1 -n -M extended',
+	0,
+	[ qr{type: .*/001_pgbench_pipeline}, qr{actually processed: 1/1} ],
+	[],
+	'working \startpipeline',
+	{
+		'001_pgbench_pipeline' => q{
+-- test startpipeline
+\startpipeline
+} . "select 1;\n" x 10 . q{
+\endpipeline
+}
+	});
+
+# Working \startpipeline in prepared query mode
+pgbench(
+	'-t 1 -n -M prepared',
+	0,
+	[ qr{type: .*/001_pgbench_pipeline_prep}, qr{actually processed: 1/1} ],
+	[],
+	'working \startpipeline',
+	{
+		'001_pgbench_pipeline_prep' => q{
+-- test startpipeline
+\startpipeline
+} . "select 1;\n" x 10 . q{
+\endpipeline
+}
+	});
+
+# Try \startpipeline twice
+pgbench(
+	'-t 1 -n -M extended',
+	2,
+	[],
+	[qr{already in pipeline mode}],
+	'error: call \startpipeline twice',
+	{
+		'001_pgbench_pipeline_2' => q{
+-- startpipeline twice
+\startpipeline
+\startpipeline
+}
+	});
+
+# Try to end a pipeline that hasn't started
+pgbench(
+	'-t 1 -n -M extended',
+	2,
+	[],
+	[qr{not in pipeline mode}],
+	'error: \endpipeline with no start',
+	{
+		'001_pgbench_pipeline_3' => q{
+-- pipeline not started
+\endpipeline
+}
+	});
+
+# Try \gset in pipeline mode
+pgbench(
+	'-t 1 -n -M extended',
+	2,
+	[],
+	[qr{gset is not allowed in pipeline mode}],
+	'error: \gset not allowed in pipeline mode',
+	{
+		'001_pgbench_pipeline_4' => q{
+\startpipeline
+select 1 \gset f
+\endpipeline
+}
+	});
+
+
 # trigger many expression errors
 my @errors = (