change_metapage_usage_hash-v2.patch

diff --git a/src/backend/access/hash/hashpage.c b/src/backend/access/hash/hashpage.c
index f279dce..185b6d7 100644
--- a/src/backend/access/hash/hashpage.c
+++ b/src/backend/access/hash/hashpage.c
@@ -403,7 +403,7 @@ _hash_init(Relation rel, double num_tuples, ForkNumber forkNum)
 
 		XLogBeginInsert();
 		XLogRegisterData((char *) &xlrec, SizeOfHashInitMetaPage);
-		XLogRegisterBuffer(0, metabuf, REGBUF_WILL_INIT);
+		XLogRegisterBuffer(0, metabuf, REGBUF_WILL_INIT | REGBUF_STANDARD);
 
 		recptr = XLogInsert(RM_HASH_ID, XLOG_HASH_INIT_META_PAGE);
 
@@ -592,8 +592,11 @@ _hash_init_metabuffer(Buffer buf, double num_tuples, RegProcedure procid,
 	metap->hashm_firstfree = 0;
 
 	/*
-	 * Set pd_lower just past the end of the metadata.  This is to log full
-	 * page image of metapage in xloginsert.c.
+	 * Set pd_lower just past the end of the metadata.  This is required for
+	 * correctness as otherwise, the pd_lower would be pointing to the
+	 * position as set by _hash_pageinit and that can lead to logging the
+	 * incorrect metadata while backing up full page image in xloginsert.c.
+	 * Note, it also helps in page masking by allowing to mask unused space.
 	 */
 	((PageHeader) page)->pd_lower =
 		((char *) metap + sizeof(HashMetaPageData)) - (char *) page;