psql: Add pipeline status to prompt and some state variables

This commit adds %P to psql prompts, able to report the status of a
pipeline depending on PQpipelineStatus(): on, off or abort.

The following variables are added to report the state of an ongoing
pipeline:
- PIPELINE_SYNC_COUNT: reports the number of piped syncs.
- PIPELINE_COMMAND_COUNT: reports the number of piped commands, a
command being either \bind, \bind_named, \close or \parse.
- PIPELINE_RESULT_COUNT: reports the results available to read with
\getresults.

These variables can be used with \echo or in a prompt, using "%:name:"
in PROMPT1, PROMPT2 or PROMPT3.  Some basic regression tests are added
for these.  The suggestion to use variables to show the details about
the status counters comes from me.  The original patch proposed was less
extensible, hardcoding the output in the prompt.

Author: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>
Discussion: https://postgr.es/m/CAO6_XqroE7JuMEm1sWz55rp9fAYX2JwmcP_3m_v51vnOFdsLiQ@mail.gmail.com

src/bin/psql/common.c

@@ -524,6 +524,26 @@ SetShellResultVariables(int wait_result)
 }
 
 
+/*
+ * Set special pipeline variables
+ * - PIPELINE_SYNC_COUNT: The number of piped syncs
+ * - PIPELINE_COMMAND_COUNT: The number of piped commands
+ * - PIPELINE_RESULT_COUNT: The number of results available to read
+ */
+static void
+SetPipelineVariables(void)
+{
+	char		buf[32];
+
+	snprintf(buf, sizeof(buf), "%d", pset.piped_syncs);
+	SetVariable(pset.vars, "PIPELINE_SYNC_COUNT", buf);
+	snprintf(buf, sizeof(buf), "%d", pset.piped_commands);
+	SetVariable(pset.vars, "PIPELINE_COMMAND_COUNT", buf);
+	snprintf(buf, sizeof(buf), "%d", pset.available_results);
+	SetVariable(pset.vars, "PIPELINE_RESULT_COUNT", buf);
+}
+
+
 /*
  * ClearOrSaveResult
  *
@@ -1661,6 +1681,8 @@ ExecQueryAndProcessResults(const char *query,
 
 		CheckConnection();
 
+		SetPipelineVariables();
+
 		return -1;
 	}
 
@@ -1669,8 +1691,10 @@ ExecQueryAndProcessResults(const char *query,
 	{
 		/*
 		 * We are in a pipeline and have not reached the pipeline end, or
-		 * there was no request to read pipeline results, exit.
+		 * there was no request to read pipeline results.  Update the psql
+		 * variables tracking the pipeline activity and exit.
 		 */
+		SetPipelineVariables();
 		return 1;
 	}
 
@@ -2105,6 +2129,7 @@ ExecQueryAndProcessResults(const char *query,
 		Assert(pset.available_results == 0);
 	}
 	Assert(pset.requested_results == 0);
+	SetPipelineVariables();
 
 	/* may need this to recover from conn loss during COPY */
 	if (!CheckConnection())

src/bin/psql/prompt.c

@@ -31,6 +31,7 @@
  *		sockets, "[local:/dir/name]" if not default
  * %m - like %M, but hostname only (before first dot), or always "[local]"
  * %p - backend pid
+ * %P - pipeline status: on, off or abort
  * %> - database server port number
  * %n - database user name
  * %s - service
@@ -181,6 +182,19 @@ get_prompt(promptStatus_t status, ConditionalStack cstack)
 							snprintf(buf, sizeof(buf), "%d", pid);
 					}
 					break;
+					/* pipeline status */
+				case 'P':
+					{
+						PGpipelineStatus status = PQpipelineStatus(pset.db);
+
+						if (status == PQ_PIPELINE_ON)
+							strlcpy(buf, "on", sizeof(buf));
+						else if (status == PQ_PIPELINE_ABORTED)
+							strlcpy(buf, "abort", sizeof(buf));
+						else
+							strlcpy(buf, "off", sizeof(buf));
+						break;
+					}
 
 				case '0':
 				case '1':

src/bin/psql/startup.c

@@ -205,6 +205,11 @@ main(int argc, char *argv[])
 	SetVariable(pset.vars, "PROMPT3", DEFAULT_PROMPT3);
 	SetVariableBool(pset.vars, "SHOW_ALL_RESULTS");
 
+	/* Initialize pipeline variables */
+	SetVariable(pset.vars, "PIPELINE_SYNC_COUNT", "0");
+	SetVariable(pset.vars, "PIPELINE_COMMAND_COUNT", "0");
+	SetVariable(pset.vars, "PIPELINE_RESULT_COUNT", "0");
+
 	parse_psql_options(argc, argv, &options);
 
 	/*

src/test/regress/expected/psql_pipeline.out

@@ -57,12 +57,24 @@ SELECT $1, $2 \bind 'val2' 'val3' \g
 
 -- Send multiple syncs
 \startpipeline
+\echo :PIPELINE_COMMAND_COUNT
+0
+\echo :PIPELINE_SYNC_COUNT
+0
+\echo :PIPELINE_RESULT_COUNT
+0
 SELECT $1 \bind 'val1' \g
 \syncpipeline
 \syncpipeline
 SELECT $1, $2 \bind 'val2' 'val3' \g
 \syncpipeline
 SELECT $1, $2 \bind 'val4' 'val5' \g
+\echo :PIPELINE_COMMAND_COUNT
+1
+\echo :PIPELINE_SYNC_COUNT
+3
+\echo :PIPELINE_RESULT_COUNT
+2
 \endpipeline
  ?column? 
 ----------
@@ -303,13 +315,21 @@ SELECT $1 \bind 2 \g
 SELECT $1 \bind 1 \g
 SELECT $1 \bind 2 \g
 SELECT $1 \bind 3 \g
+\echo :PIPELINE_SYNC_COUNT
+0
 \syncpipeline
+\echo :PIPELINE_SYNC_COUNT
+1
+\echo :PIPELINE_RESULT_COUNT
+3
 \getresults 1
  ?column? 
 ----------
  1
 (1 row)
 
+\echo :PIPELINE_RESULT_COUNT
+2
 SELECT $1 \bind 4 \g
 \getresults 3
  ?column? 
@@ -322,6 +342,8 @@ SELECT $1 \bind 4 \g
  3
 (1 row)
 
+\echo :PIPELINE_RESULT_COUNT
+0
 \endpipeline
  ?column? 
 ----------

src/test/regress/sql/psql_pipeline.sql

@@ -27,12 +27,18 @@ SELECT $1, $2 \bind 'val2' 'val3' \g
 
 -- Send multiple syncs
 \startpipeline
+\echo :PIPELINE_COMMAND_COUNT
+\echo :PIPELINE_SYNC_COUNT
+\echo :PIPELINE_RESULT_COUNT
 SELECT $1 \bind 'val1' \g
 \syncpipeline
 \syncpipeline
 SELECT $1, $2 \bind 'val2' 'val3' \g
 \syncpipeline
 SELECT $1, $2 \bind 'val4' 'val5' \g
+\echo :PIPELINE_COMMAND_COUNT
+\echo :PIPELINE_SYNC_COUNT
+\echo :PIPELINE_RESULT_COUNT
 \endpipeline
 
 -- \startpipeline should not have any effect if already in a pipeline.
@@ -174,10 +180,15 @@ SELECT $1 \bind 2 \g
 SELECT $1 \bind 1 \g
 SELECT $1 \bind 2 \g
 SELECT $1 \bind 3 \g
+\echo :PIPELINE_SYNC_COUNT
 \syncpipeline
+\echo :PIPELINE_SYNC_COUNT
+\echo :PIPELINE_RESULT_COUNT
 \getresults 1
+\echo :PIPELINE_RESULT_COUNT
 SELECT $1 \bind 4 \g
 \getresults 3
+\echo :PIPELINE_RESULT_COUNT
 \endpipeline
 
 -- \syncpipeline count as one command to fetch for \getresults.