pgbench: Add \syncpipeline

This change adds a new meta-command called \syncpipeline to pgbench,
able to send a sync message without flushing using the new libpq
function PQsendPipelineSync().

This meta-command is available within a block made of \startpipeline and
\endpipeline.

Author: Anthonin Bonnefoy
Discussion: https://postgr.es/m/CAO6_XqpcNhW6LZHLF-2NpPzdTbyMm4-RVkr3+AP5cOKSm9hrWA@mail.gmail.com

Author: michaelpq

doc/src/sgml/ref/pgbench.sgml

@@ -1386,13 +1386,19 @@ SELECT 4 AS four \; SELECT 5 AS five \aset
 
    <varlistentry id="pgbench-metacommand-pipeline">
     <term><literal>\startpipeline</literal></term>
+    <term><literal>\syncpipeline</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
+        This group of commands implements pipelining of SQL statements.
+        A pipeline must begin with a <command>\startpipeline</command>
+        and end with an <command>\endpipeline</command>. In between there
+        may be any number of <command>\syncpipeline</command> commands,
+        which sends a <link linkend="protocol-flow-ext-query">sync message</link>
+        without ending the ongoing pipeline and flushing the send buffer.
+        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>

src/bin/pgbench/pgbench.c

@@ -608,6 +608,7 @@ typedef struct
 
 	int			use_file;		/* index in sql_script for this client */
 	int			command;		/* command number in script */
+	int			num_syncs;		/* number of ongoing sync commands */
 
 	/* client variables */
 	Variables	variables;
@@ -697,6 +698,7 @@ typedef enum MetaCommand
 	META_ELSE,					/* \else */
 	META_ENDIF,					/* \endif */
 	META_STARTPIPELINE,			/* \startpipeline */
+	META_SYNCPIPELINE,			/* \syncpipeline */
 	META_ENDPIPELINE,			/* \endpipeline */
 } MetaCommand;
 
@@ -2902,6 +2904,8 @@ getMetaCommand(const char *cmd)
 		mc = META_ASET;
 	else if (pg_strcasecmp(cmd, "startpipeline") == 0)
 		mc = META_STARTPIPELINE;
+	else if (pg_strcasecmp(cmd, "syncpipeline") == 0)
+		mc = META_SYNCPIPELINE;
 	else if (pg_strcasecmp(cmd, "endpipeline") == 0)
 		mc = META_ENDPIPELINE;
 	else
@@ -3317,8 +3321,10 @@ readCommandResponse(CState *st, MetaCommand meta, char *varprefix)
 				break;
 
 			case PGRES_PIPELINE_SYNC:
-				pg_log_debug("client %d pipeline ending", st->id);
-				if (PQexitPipelineMode(st->con) != 1)
+				pg_log_debug("client %d pipeline ending, ongoing syncs: %d",
+							 st->id, st->num_syncs);
+				st->num_syncs--;
+				if (st->num_syncs == 0 && PQexitPipelineMode(st->con) != 1)
 					pg_log_error("client %d failed to exit pipeline mode: %s", st->id,
 								 PQerrorMessage(st->con));
 				break;
@@ -4449,6 +4455,20 @@ executeMetaCommand(CState *st, pg_time_usec_t *now)
 			return CSTATE_ABORTED;
 		}
 	}
+	else if (command->meta == META_SYNCPIPELINE)
+	{
+		if (PQpipelineStatus(st->con) != PQ_PIPELINE_ON)
+		{
+			commandFailed(st, "syncpipeline", "not in pipeline mode");
+			return CSTATE_ABORTED;
+		}
+		if (PQsendPipelineSync(st->con) == 0)
+		{
+			commandFailed(st, "syncpipeline", "failed to send a pipeline sync");
+			return CSTATE_ABORTED;
+		}
+		st->num_syncs++;
+	}
 	else if (command->meta == META_ENDPIPELINE)
 	{
 		if (PQpipelineStatus(st->con) != PQ_PIPELINE_ON)
@@ -4461,6 +4481,7 @@ executeMetaCommand(CState *st, pg_time_usec_t *now)
 			commandFailed(st, "endpipeline", "failed to send a pipeline sync");
 			return CSTATE_ABORTED;
 		}
+		st->num_syncs++;
 		/* 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;
@@ -5794,7 +5815,8 @@ process_backslash_command(PsqlScanState sstate, const char *source)
 	}
 	else if (my_command->meta == META_ELSE || my_command->meta == META_ENDIF ||
 			 my_command->meta == META_STARTPIPELINE ||
-			 my_command->meta == META_ENDPIPELINE)
+			 my_command->meta == META_ENDPIPELINE ||
+			 my_command->meta == META_SYNCPIPELINE)
 	{
 		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

@@ -814,6 +814,27 @@ sub check_data_state
 }
 	});
 
+# Working \startpipeline with \syncpipeline
+$node->pgbench(
+	'-t 1 -n -M extended',
+	0,
+	[ qr{type: .*/001_pgbench_pipeline_sync}, qr{actually processed: 1/1} ],
+	[],
+	'working \startpipeline with \syncpipeline',
+	{
+		'001_pgbench_pipeline_sync' => q{
+-- test startpipeline
+\startpipeline
+select 1;
+\syncpipeline
+\syncpipeline
+select 2;
+\syncpipeline
+select 3;
+\endpipeline
+}
+	});
+
 # Working \startpipeline in prepared query mode
 $node->pgbench(
 	'-t 1 -n -M prepared',
@@ -904,6 +925,21 @@ sub check_data_state
 }
 	});
 
+# Try \startpipeline with \syncpipeline without \endpipeline
+$node->pgbench(
+	'-t 2 -n -M extended',
+	2,
+	[],
+	[qr{end of script reached with pipeline open}],
+	'error: call \startpipeline and \syncpipeline without \endpipeline',
+	{
+		'001_pgbench_pipeline_7' => q{
+-- startpipeline with \syncpipeline only
+\startpipeline
+\syncpipeline
+}
+	});
+
 # Working \startpipeline in prepared query mode with serializable
 $node->pgbench(
 	'-c4 -t 10 -n -M prepared',