From d988c86d60d2b49b52e547b42c644493a377d44a Mon Sep 17 00:00:00 2001
From: Matthias van de Meent <boekewurm+postgres@gmail.com>
Date: Thu, 7 Jan 2021 16:39:57 +0100
Subject: [PATCH v1 1/2] Add progress reporting for filtered rows.

COPY ... FROM ... WHERE (condition) may drop rows, which we now register as
explicitly being dropped.
---
 doc/src/sgml/monitoring.sgml         | 10 ++++++++++
 src/backend/catalog/system_views.sql |  3 ++-
 src/backend/commands/copyfrom.c      |  5 +++++
 src/include/commands/progress.h      |  1 +
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 43fe8ae383..bf18ea23bd 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -6498,6 +6498,16 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
        Number of lines already processed by <command>COPY</command> command.
       </para></entry>
      </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>lines_filtered</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of lines not processed due to being filtered by the
+       <command>WHERE</command> clause of the <command>COPY</command> command.
+      </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 5d89e77dbe..83d62c5286 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1124,7 +1124,8 @@ CREATE VIEW pg_stat_progress_copy AS
         S.relid AS relid,
         S.param1 AS bytes_processed,
         S.param2 AS bytes_total,
-        S.param3 AS lines_processed
+        S.param3 AS lines_processed,
+        S.param4 AS lines_filtered
     FROM pg_stat_get_progress_info('COPY') AS S
         LEFT JOIN pg_database D ON S.datid = D.oid;
 
diff --git a/src/backend/commands/copyfrom.c b/src/backend/commands/copyfrom.c
index 08b6f782c7..212f4c67d6 100644
--- a/src/backend/commands/copyfrom.c
+++ b/src/backend/commands/copyfrom.c
@@ -540,6 +540,7 @@ CopyFrom(CopyFromState cstate)
 	CopyInsertMethod insertMethod;
 	CopyMultiInsertInfo multiInsertInfo = {0};	/* pacify compiler */
 	uint64		processed = 0;
+	uint64		filtered = 0;
 	bool		has_before_insert_row_trig;
 	bool		has_instead_insert_row_trig;
 	bool		leafpart_use_multi_insert = false;
@@ -868,7 +869,11 @@ CopyFrom(CopyFromState cstate)
 			econtext->ecxt_scantuple = myslot;
 			/* Skip items that don't match COPY's WHERE clause */
 			if (!ExecQual(cstate->qualexpr, econtext))
+			{
+				/* Report that this tuple was filtered out by the WHERE clause */
+				pgstat_progress_update_param(PROGRESS_COPY_LINES_FILTERED, ++filtered);
 				continue;
+			}
 		}
 
 		/* Determine the partition to insert the tuple into */
diff --git a/src/include/commands/progress.h b/src/include/commands/progress.h
index 95ec5d02e9..eb0f4e70d6 100644
--- a/src/include/commands/progress.h
+++ b/src/include/commands/progress.h
@@ -137,5 +137,6 @@
 #define PROGRESS_COPY_BYTES_PROCESSED 0
 #define PROGRESS_COPY_BYTES_TOTAL 1
 #define PROGRESS_COPY_LINES_PROCESSED 2
+#define PROGRESS_COPY_LINES_FILTERED 3
 
 #endif
-- 
2.20.1