Reintroduce dead tuple counter in pg_stat_progress_vacuum.

Commit 667e65aac3 changed both num_dead_tuples and max_dead_tuples
columns to dead_tuple_bytes and max_dead_tuple_bytes columns,
respectively. But as per discussion, the number of dead tuples
collected still provides meaningful insights for users.

This commit reintroduces the column for the count of dead tuples,
renamed as num_dead_item_ids. It avoids confusion with the number of
dead tuples removed by VACUUM, which includes dead heap-only tuples
but excludes any pre-existing LP_DEAD items left behind by
opportunistic pruning.

Bump catalog version.

Reviewed-by: Peter Geoghegan, Álvaro Herrera, Andrey Borodin
Discussion: https://postgr.es/m/CAD21AoBL5sJE9TRWPyv%2Bw7k5Ee5QAJqDJEDJBUdAaCzGWAdvZw%40mail.gmail.com

doc/src/sgml/monitoring.sgml

@@ -6268,6 +6268,15 @@ FROM pg_stat_get_backend_idset() AS backendid;
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+      <structfield>num_dead_item_ids</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of dead item identifiers collected since the last index vacuum cycle.
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>indexes_total</structfield> <type>bigint</type>

src/backend/access/heap/vacuumlazy.c

@@ -2883,13 +2883,19 @@ dead_items_add(LVRelState *vacrel, BlockNumber blkno, OffsetNumber *offsets,
 			   int num_offsets)
 {
 	TidStore   *dead_items = vacrel->dead_items;
+	const int	prog_index[2] = {
+		PROGRESS_VACUUM_NUM_DEAD_ITEM_IDS,
+		PROGRESS_VACUUM_DEAD_TUPLE_BYTES
+	};
+	int64		prog_val[2];
 
 	TidStoreSetBlockOffsets(dead_items, blkno, offsets, num_offsets);
 	vacrel->dead_items_info->num_items += num_offsets;
 
-	/* update the memory usage report */
-	pgstat_progress_update_param(PROGRESS_VACUUM_DEAD_TUPLE_BYTES,
-								 TidStoreMemoryUsage(dead_items));
+	/* update the progress information */
+	prog_val[0] = vacrel->dead_items_info->num_items;
+	prog_val[1] = TidStoreMemoryUsage(dead_items);
+	pgstat_progress_update_multi_param(2, prog_index, prog_val);
 }
 
 /*

src/backend/catalog/system_views.sql

@@ -1221,7 +1221,8 @@ CREATE VIEW pg_stat_progress_vacuum AS
         S.param2 AS heap_blks_total, S.param3 AS heap_blks_scanned,
         S.param4 AS heap_blks_vacuumed, S.param5 AS index_vacuum_count,
         S.param6 AS max_dead_tuple_bytes, S.param7 AS dead_tuple_bytes,
-        S.param8 AS indexes_total, S.param9 AS indexes_processed
+        S.param8 AS num_dead_item_ids, S.param9 AS indexes_total,
+        S.param10 AS indexes_processed
     FROM pg_stat_get_progress_info('VACUUM') AS S
         LEFT JOIN pg_database D ON S.datid = D.oid;
 

src/include/catalog/catversion.h

@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202405161
+#define CATALOG_VERSION_NO	202406141
 
 #endif

src/include/commands/progress.h

@@ -25,8 +25,9 @@
 #define PROGRESS_VACUUM_NUM_INDEX_VACUUMS		4
 #define PROGRESS_VACUUM_MAX_DEAD_TUPLE_BYTES	5
 #define PROGRESS_VACUUM_DEAD_TUPLE_BYTES		6
-#define PROGRESS_VACUUM_INDEXES_TOTAL			7
-#define PROGRESS_VACUUM_INDEXES_PROCESSED		8
+#define PROGRESS_VACUUM_NUM_DEAD_ITEM_IDS		7
+#define PROGRESS_VACUUM_INDEXES_TOTAL			8
+#define PROGRESS_VACUUM_INDEXES_PROCESSED		9
 
 /* Phases of vacuum (as advertised via PROGRESS_VACUUM_PHASE) */
 #define PROGRESS_VACUUM_PHASE_SCAN_HEAP			1

src/test/regress/expected/rules.out

@@ -2052,8 +2052,9 @@ pg_stat_progress_vacuum| SELECT s.pid,
     s.param5 AS index_vacuum_count,
     s.param6 AS max_dead_tuple_bytes,
     s.param7 AS dead_tuple_bytes,
-    s.param8 AS indexes_total,
-    s.param9 AS indexes_processed
+    s.param8 AS num_dead_item_ids,
+    s.param9 AS indexes_total,
+    s.param10 AS indexes_processed
    FROM (pg_stat_get_progress_info('VACUUM'::text) s(pid, datid, relid, param1, param2, param3, param4, param5, param6, param7, param8, param9, param10, param11, param12, param13, param14, param15, param16, param17, param18, param19, param20)
      LEFT JOIN pg_database d ON ((s.datid = d.oid)));
 pg_stat_recovery_prefetch| SELECT stats_reset,