Fix briefly showing old progress stats for ANALYZE on inherited tables.

ANALYZE on a table with inheritance children analyzes all the child
tables in a loop. When stepping to next child table, it updated the
child rel ID value in the command progress stats, but did not reset
the 'sample_blks_total' and 'sample_blks_scanned' counters.
acquire_sample_rows() updates 'sample_blks_total' as soon as the scan
starts and 'sample_blks_scanned' after processing the first block, but
until then, pg_stat_progress_analyze would display a bogus combination
of the new child table relid with old counter values from the
previously processed child table. Fix by resetting 'sample_blks_total'
and 'sample_blks_scanned' to zero at the same time that
'current_child_table_relid' is updated.

Backpatch to v13, where pg_stat_progress_analyze view was introduced.

Reported-by: Justin Pryzby
Discussion: https://www.postgresql.org/message-id/20230122162345.GP13860%40telsasoft.com

Author: hlinnaka

src/backend/commands/analyze.c

@@ -1531,8 +1531,25 @@ acquire_inherited_sample_rows(Relation onerel, int elevel,
 		AcquireSampleRowsFunc acquirefunc = acquirefuncs[i];
 		double		childblocks = relblocks[i];
 
-		pgstat_progress_update_param(PROGRESS_ANALYZE_CURRENT_CHILD_TABLE_RELID,
-									 RelationGetRelid(childrel));
+		/*
+		 * Report progress.  The sampling function will normally report blocks
+		 * done/total, but we need to reset them to 0 here, so that they don't
+		 * show an old value until that.
+		 */
+		{
+			const int	progress_index[] = {
+				PROGRESS_ANALYZE_CURRENT_CHILD_TABLE_RELID,
+				PROGRESS_ANALYZE_BLOCKS_DONE,
+				PROGRESS_ANALYZE_BLOCKS_TOTAL
+			};
+			const int64 progress_vals[] = {
+				RelationGetRelid(childrel),
+				0,
+				0,
+			};
+
+			pgstat_progress_update_multi_param(3, progress_index, progress_vals);
+		}
 
 		if (childblocks > 0)
 		{