change_metapage_usage_btree-v3.patch

diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c
index bf963fc..5cbaba1 100644
--- a/src/backend/access/nbtree/nbtinsert.c
+++ b/src/backend/access/nbtree/nbtinsert.c
@@ -898,7 +898,7 @@ _bt_insertonpg(Relation rel,
 				xlmeta.fastroot = metad->btm_fastroot;
 				xlmeta.fastlevel = metad->btm_fastlevel;
 
-				XLogRegisterBuffer(2, metabuf, REGBUF_WILL_INIT);
+				XLogRegisterBuffer(2, metabuf, REGBUF_WILL_INIT | REGBUF_STANDARD);
 				XLogRegisterBufData(2, (char *) &xlmeta, sizeof(xl_btree_metadata));
 
 				xlinfo = XLOG_BTREE_INSERT_META;
@@ -2032,7 +2032,7 @@ _bt_newroot(Relation rel, Buffer lbuf, Buffer rbuf)
 
 		XLogRegisterBuffer(0, rootbuf, REGBUF_WILL_INIT);
 		XLogRegisterBuffer(1, lbuf, REGBUF_STANDARD);
-		XLogRegisterBuffer(2, metabuf, REGBUF_WILL_INIT);
+		XLogRegisterBuffer(2, metabuf, REGBUF_WILL_INIT | REGBUF_STANDARD);
 
 		md.root = rootblknum;
 		md.level = metad->btm_level;
diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c
index 10697e9..c774349 100644
--- a/src/backend/access/nbtree/nbtpage.c
+++ b/src/backend/access/nbtree/nbtpage.c
@@ -65,8 +65,9 @@ _bt_initmetapage(Page page, BlockNumber rootbknum, uint32 level)
 	metaopaque->btpo_flags = BTP_META;
 
 	/*
-	 * Set pd_lower just past the end of the metadata.  This is not essential
-	 * but it makes the page look compressible to xlog.c.
+	 * Set pd_lower just past the end of the metadata.  This is essential,
+	 * because without doing so, metadata will be lost if xlog.c compresses
+	 * the page.
 	 */
 	((PageHeader) page)->pd_lower =
 		((char *) metad + sizeof(BTMetaPageData)) - (char *) page;
@@ -241,7 +242,7 @@ _bt_getroot(Relation rel, int access)
 
 			XLogBeginInsert();
 			XLogRegisterBuffer(0, rootbuf, REGBUF_WILL_INIT);
-			XLogRegisterBuffer(2, metabuf, REGBUF_WILL_INIT);
+			XLogRegisterBuffer(2, metabuf, REGBUF_WILL_INIT | REGBUF_STANDARD);
 
 			md.root = rootblkno;
 			md.level = 0;
@@ -1827,7 +1828,7 @@ _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, bool *rightsib_empty)
 
 		if (BufferIsValid(metabuf))
 		{
-			XLogRegisterBuffer(4, metabuf, REGBUF_WILL_INIT);
+			XLogRegisterBuffer(4, metabuf, REGBUF_WILL_INIT | REGBUF_STANDARD);
 
 			xlmeta.root = metad->btm_root;
 			xlmeta.level = metad->btm_level;
diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c
index 3dbafdd..399e6a1 100644
--- a/src/backend/access/nbtree/nbtree.c
+++ b/src/backend/access/nbtree/nbtree.c
@@ -298,7 +298,7 @@ btbuildempty(Relation index)
 	smgrwrite(index->rd_smgr, INIT_FORKNUM, BTREE_METAPAGE,
 			  (char *) metapage, true);
 	log_newpage(&index->rd_smgr->smgr_rnode.node, INIT_FORKNUM,
-				BTREE_METAPAGE, metapage, false);
+				BTREE_METAPAGE, metapage, true);
 
 	/*
 	 * An immediate sync is required even if we xlog'd the page, because the
diff --git a/src/backend/access/nbtree/nbtxlog.c b/src/backend/access/nbtree/nbtxlog.c
index 82337f8..7250b4f 100644
--- a/src/backend/access/nbtree/nbtxlog.c
+++ b/src/backend/access/nbtree/nbtxlog.c
@@ -107,8 +107,9 @@ _bt_restore_meta(XLogReaderState *record, uint8 block_id)
 	pageop->btpo_flags = BTP_META;
 
 	/*
-	 * Set pd_lower just past the end of the metadata.  This is not essential
-	 * but it makes the page look compressible to xlog.c.
+	 * Set pd_lower just past the end of the metadata.  This is essential,
+	 * because without doing so, metadata will be lost if xlog.c compresses
+	 * the page.
 	 */
 	((PageHeader) metapg)->pd_lower =
 		((char *) md + sizeof(BTMetaPageData)) - (char *) metapg;