Date: Wed, 01 Jul 2026 21:18:05 +0900 (JST)
Message-Id: <20260701.211805.2273383346456030984.ishii@postgresql.org>
To: assam258@gmail.com, jian.universality@gmail.com
Cc: pgsql-hackers@postgresql.org, zsolt.parragi@percona.com,
 sjjang112233@gmail.com, vik@postgresfriends.org, er@xs4all.nl,
 jacob.champion@enterprisedb.com, david.g.johnston@gmail.com,
 peter@eisentraut.org, li.evan.chao@gmail.com
Subject: Re: Row pattern recognition
From: Tatsuo Ishii <ishii@postgresql.org>
In-Reply-To: <20260629.183730.1799088184925453299.ishii@postgresql.org>
References: <20260622.215536.1729984032454200237.ishii@postgresql.org>
	<CAAAe_zChW=nM9J18wdF2wMa2KesFO53fkbVRudkJ_bstdxzfOQ@mail.gmail.com>
	<20260629.183730.1799088184925453299.ishii@postgresql.org>
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> Will continue reviewes tomorrow.

Sorry for delay. Here is the review for
v50-0005-match-once-per-row.patch.

--- a/src/backend/executor/nodeWindowAgg.c
+++ b/src/backend/executor/nodeWindowAgg.c
@@ -239,6 +239,10 @@ static int64 row_is_in_reduced_frame(WindowObject winobj, int64 pos);
 
 static void clear_reduced_frame(WindowAggState *winstate);
 static int	get_reduced_frame_status(WindowAggState *winstate, int64 pos);
+static void advance_nav_mark(WindowAggState *winstate, int64 currentPos);
+static void advance_reduced_frame_nfa(WindowObject winobj,
+									  RPRNFAContext *targetCtx, int64 pos,
+									  bool hasLimitedFrame, int64 frameOffset);
 static void update_reduced_frame(WindowObject winobj, int64 pos);
 
 /* Forward declarations - NFA row evaluation */
@@ -2521,6 +2525,16 @@ ExecWindowAgg(PlanState *pstate)
 			{
 				if (winstate->rpSkipTo == ST_NEXT_ROW)
 					clear_reduced_frame(winstate);
+
+				/*
+				 * Drive the row pattern match every row, so it tracks the row
+				 * scan rather than frame access: a window function that skips
+				 * the frame (e.g. nth_value() with a NULL offset) must not
+				 * leave the match state behind currentpos.
+				 */
+				Assert(winstate->nav_winobj != NULL);
+				(void) row_is_in_reduced_frame(winstate->nav_winobj,
+											   winstate->currentpos);

Is there any reason that we call row_is_in_reduced_frame() here,
instead of something like:

   update_frameheadpos(winstate);
   update_reduced_frame(winobj, pos);

row_is_in_reduced_frame() returns row status. Ignoring it using (void)
looks a little bit confusing to me.

Regards,
--
Tatsuo Ishii
SRA OSS K.K.
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp