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commit    f56a9def71bb1d2ccf4fa01a4d1e082c1063d921
Author:   Michael Paquier <michael@paquier.xyz>
Date:     Thu Apr 11 00:20:51 2024 +0000
First released in: 17.0

    Fix inconsistency with replay of hash squeeze record for clean buffers
    
    aa5edbe379d6 has tweaked _hash_freeovflpage() so as the write buffer's
    LSN is updated only when necessary, when REGBUF_NO_CHANGE is not used.
    
    The replay code was not consistent with that, causing the write buffer's
    LSN to be updated and its page to be marked as dirty even if the buffer
    was registered in a "clean" state.  This was possible for the case of a
    squeeze record when there are no tuples to add to the write buffer, for
    (is_prim_bucket_same_wrt && !is_prev_bucket_same_wrt).
    
    I have performed some validation of this commit with
    wal_consistency_checking and a change in WAL that logs REGBUF_NO_CHANGE
    to a new BKPIMAGE_*.  Thanks to that, it is possible to know at replay
    if a buffer was clean when it was registered, then cross-checked the LSN
    of the "clean" page copy coming from WAL with the LSN of the block once
    the record has been replayed.  This eats one bit in bimg_info, which is
    not acceptable to be integrated as-is, but it could become handy in the
    future.  I didn't spot other areas than the one fixed by this commit at
    the extent of what the main regression test suite covers.
    
    As this is an oversight in aa5edbe379d6, no backpatch is required.
    
    Reported-by: Zubeyr Eryilmaz
    Author: Hayato Kuroda
    Reviewed-by: Amit Kapila, Michael Paquier
    Discussion: https://postgr.es/m/ZbyVVG_7eW3YD5-A@paquier.xyz


 src/backend/access/hash/hash_xlog.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/backend/access/hash/hash_xlog.c b/src/backend/access/hash/hash_xlog.c
index cb1a63cfeec..4e1ec468569 100644
--- a/src/backend/access/hash/hash_xlog.c
+++ b/src/backend/access/hash/hash_xlog.c
@@ -666,6 +666,7 @@ hash_xlog_squeeze_page(XLogReaderState *record)
 		char	   *data;
 		Size		datalen;
 		uint16		ninserted = 0;
+		bool		mod_wbuf = false;
 
 		data = begin = XLogRecGetBlockData(record, 1, &datalen);
 
@@ -695,6 +696,17 @@ hash_xlog_squeeze_page(XLogReaderState *record)
 
 				ninserted++;
 			}
+
+			mod_wbuf = true;
+		}
+		else
+		{
+			/*
+			 * Ensure that the required flags are set when there are no
+			 * tuples.  See _hash_freeovflpage().
+			 */
+			Assert(xldata->is_prim_bucket_same_wrt ||
+				   xldata->is_prev_bucket_same_wrt);
 		}
 
 		/*
@@ -711,10 +723,15 @@ hash_xlog_squeeze_page(XLogReaderState *record)
 			HashPageOpaque writeopaque = HashPageGetOpaque(writepage);
 
 			writeopaque->hasho_nextblkno = xldata->nextblkno;
+			mod_wbuf = true;
 		}
 
-		PageSetLSN(writepage, lsn);
-		MarkBufferDirty(writebuf);
+		/* Set LSN and mark writebuf dirty iff it is modified */
+		if (mod_wbuf)
+		{
+			PageSetLSN(writepage, lsn);
+			MarkBufferDirty(writebuf);
+		}
 	}
 
 	/* replay the record for initializing overflow buffer */


[parent: 5392dd3d2ad5]