MDEV-17138 follow-up: Optimize index page creation

btr_create(), btr_root_raise_and_insert(): Write a MLOG_MEMSET record
to set FIL_PAGE_PREV,FIL_PAGE_NEXT to FIL_NULL, instead of writing
two MLOG_4BYTES records.

For ROW_FORMAT=COMPRESSED pages, we will not use MLOG_MEMSET
because we want the crash-downgrade to earlier 10.4 releases to succeed.

mlog_parse_nbytes(): Relax the too strict assertion. There is no problem
with MLOG_MEMSET records that affect the uncompressed header of
ROW_FORMAT=COMPRESSED index pages.

storage/innobase/btr/btr0btr.cc

@@ -1156,8 +1156,23 @@ btr_create(
 	btr_page_set_index_id(page, page_zip, index_id, mtr);
 
 	/* Set the next node and previous node fields */
-	btr_page_set_next(page, page_zip, FIL_NULL, mtr);
-	btr_page_set_prev(page, page_zip, FIL_NULL, mtr);
+	compile_time_assert(FIL_PAGE_NEXT == FIL_PAGE_PREV + 4);
+	compile_time_assert(FIL_NULL == 0xffffffff);
+#if MYSQL_VERSION_ID < 100500
+	if (UNIV_LIKELY_NULL(page_zip)) {
+		/* Avoid tripping the ut_a() in mlog_parse_nbytes()
+		when crash-downgrading to an earlier MariaDB 10.4 version. */
+		btr_page_set_next(page, page_zip, FIL_NULL, mtr);
+		btr_page_set_prev(page, page_zip, FIL_NULL, mtr);
+	} else {
+		mlog_memset(block, FIL_PAGE_PREV, 8, 0xff, mtr);
+	}
+#else
+	mlog_memset(block, FIL_PAGE_PREV, 8, 0xff, mtr);
+	if (UNIV_LIKELY_NULL(page_zip)) {
+		memset(page_zip->data + FIL_PAGE_PREV, 0xff, 8);
+	}
+#endif
 
 	/* We reset the free bits for the page in a separate
 	mini-transaction to allow creation of several trees in the
@@ -1934,8 +1949,23 @@ btr_root_raise_and_insert(
 	btr_page_create(new_block, new_page_zip, index, level, mtr);
 
 	/* Set the next node and previous node fields of new page */
-	btr_page_set_next(new_page, new_page_zip, FIL_NULL, mtr);
-	btr_page_set_prev(new_page, new_page_zip, FIL_NULL, mtr);
+	compile_time_assert(FIL_PAGE_NEXT == FIL_PAGE_PREV + 4);
+	compile_time_assert(FIL_NULL == 0xffffffff);
+#if MYSQL_VERSION_ID < 100500
+	if (UNIV_LIKELY_NULL(new_page_zip)) {
+		/* Avoid tripping the ut_a() in mlog_parse_nbytes()
+		when crash-downgrading to an earlier MariaDB 10.4 version. */
+		btr_page_set_next(new_page, new_page_zip, FIL_NULL, mtr);
+		btr_page_set_prev(new_page, new_page_zip, FIL_NULL, mtr);
+	} else {
+		mlog_memset(new_block, FIL_PAGE_PREV, 8, 0xff, mtr);
+	}
+#else
+	mlog_memset(new_block, FIL_PAGE_PREV, 8, 0xff, mtr);
+	if (UNIV_LIKELY_NULL(new_page_zip)) {
+		memset(new_page_zip->data + FIL_PAGE_PREV, 0xff, 8);
+	}
+#endif
 
 	/* Copy the records from root to the new page one by one. */
 

storage/innobase/mtr/mtr0log.cc

 /*****************************************************************************
 
 Copyright (c) 1995, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2018, MariaDB Corporation.
+Copyright (c) 2017, 2019, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -139,6 +139,7 @@ mlog_parse_nbytes(
 
 	ut_ad(type <= MLOG_8BYTES || type == MLOG_MEMSET);
 	ut_a(!page || !page_zip
+	     || type == MLOG_MEMSET
 	     || !fil_page_index_page_check(page));
 	if (end_ptr < ptr + 2) {
 		return NULL;
@@ -164,6 +165,8 @@ mlog_parse_nbytes(
 		if (page) {
 			memset(page + offset, *ptr, val);
 			if (page_zip) {
+				ut_ad(offset + val <= PAGE_DATA
+				      || !fil_page_index_page_check(page));
 				memset(static_cast<page_zip_des_t*>(page_zip)
 				       ->data + offset, *ptr, val);
 			}