MDEV-6076: Preserve PAGE_ROOT_AUTO_INC when emptying pages.

Thanks to Zhangyuan from Alibaba for pointing out this bug.

btr_page_empty(): When a clustered index root page is emptied,
preserve PAGE_ROOT_AUTO_INC. This would occur during a page split.

page_create_empty(): Preserve PAGE_ROOT_AUTO_INC when a clustered
index root page becomes empty. Use a faster method for writing
the field.

page_zip_copy_recs(): Reset PAGE_MAX_TRX_ID when copying
clustered index pages. We must clear the field when the root page
was a leaf page and it is being split, so that PAGE_MAX_TRX_ID
will continue to be 0 in clustered index non-root pages.

page_create_zip(): Add debug assertions for validating
PAGE_MAX_TRX_ID and PAGE_ROOT_AUTO_INC.

mysql-test/suite/innodb/r/autoinc_persist.result

@@ -629,6 +629,16 @@ ERROR 0A000: LOCK=NONE is not supported. Reason: Adding an auto-increment column
 ALTER TABLE mdev6076a ADD COLUMN a SERIAL FIRST, ALGORITHM=INPLACE;
 ALTER TABLE mdev6076b ADD COLUMN a SERIAL FIRST, AUTO_INCREMENT=100,
 ALGORITHM=INPLACE;
+# MDEV-6076: Test root page split and page_create_empty()
+CREATE TABLE mdev6076empty (b SERIAL, pad CHAR(255) NOT NULL DEFAULT '')
+ENGINE=InnoDB;
+BEGIN;
+# Insert records in descending order of AUTO_INCREMENT,
+# causing a page split on the very last insert.
+# Without the fix in btr_page_empty() this would lose the counter value.
+# Without the fix in page_create_empty() the counter value would be lost
+# when ROLLBACK deletes the last row.
+ROLLBACK;
 # Kill and restart
 INSERT INTO t3 VALUES(0);
 SELECT MAX(a) AS `Expect 120` FROM t3;
@@ -646,7 +656,11 @@ a	b
 100	2
 101	1
 102	NULL
-DROP TABLE mdev6076a, mdev6076b;
+INSERT INTO mdev6076empty SET b=NULL;
+SELECT * FROM mdev6076empty;
+b	pad
+56	
+DROP TABLE mdev6076a, mdev6076b, mdev6076empty;
 INSERT INTO t3 VALUES(0), (0), (200), (210);
 # Test the different algorithms in ALTER TABLE
 CREATE TABLE t_inplace LIKE t3;

mysql-test/suite/innodb/t/autoinc_persist.test

@@ -382,6 +382,23 @@ ALTER TABLE mdev6076a ADD COLUMN a SERIAL FIRST, LOCK=NONE;
 ALTER TABLE mdev6076a ADD COLUMN a SERIAL FIRST, ALGORITHM=INPLACE;
 ALTER TABLE mdev6076b ADD COLUMN a SERIAL FIRST, AUTO_INCREMENT=100,
 ALGORITHM=INPLACE;
+--echo # MDEV-6076: Test root page split and page_create_empty()
+CREATE TABLE mdev6076empty (b SERIAL, pad CHAR(255) NOT NULL DEFAULT '')
+ENGINE=InnoDB;
+BEGIN;
+--echo # Insert records in descending order of AUTO_INCREMENT,
+--echo # causing a page split on the very last insert.
+--echo # Without the fix in btr_page_empty() this would lose the counter value.
+--echo # Without the fix in page_create_empty() the counter value would be lost
+--echo # when ROLLBACK deletes the last row.
+--disable_query_log
+let $i= 55;
+while ($i) {
+ eval INSERT INTO mdev6076empty SET b=$i;
+ dec $i;
+}
+--enable_query_log
+ROLLBACK;
 
 --source include/kill_and_restart_mysqld.inc
 
@@ -392,7 +409,9 @@ INSERT INTO mdev6076a SET b=NULL;
 SELECT * FROM mdev6076a;
 INSERT INTO mdev6076b SET b=NULL;
 SELECT * FROM mdev6076b;
-DROP TABLE mdev6076a, mdev6076b;
+INSERT INTO mdev6076empty SET b=NULL;
+SELECT * FROM mdev6076empty;
+DROP TABLE mdev6076a, mdev6076b, mdev6076empty;
 
 INSERT INTO t3 VALUES(0), (0), (200), (210);
 

storage/innobase/btr/btr0btr.cc

@@ -1867,12 +1867,23 @@ btr_page_empty(
 	/* Recreate the page: note that global data on page (possible
 	segment headers, next page-field, etc.) is preserved intact */
 
+	/* Preserve PAGE_ROOT_AUTO_INC when creating a clustered index
+	root page. */
+	const ib_uint64_t	autoinc
+		= dict_index_is_clust(index) && page_is_root(page)
+		? page_get_autoinc(page)
+		: 0;
+
 	if (page_zip) {
-		page_create_zip(block, index, level, 0, NULL, mtr);
+		page_create_zip(block, index, level, autoinc, NULL, mtr);
 	} else {
 		page_create(block, mtr, dict_table_is_comp(index->table),
 			    dict_index_is_spatial(index));
 		btr_page_set_level(page, NULL, level, mtr);
+		if (autoinc) {
+			mlog_write_ull(PAGE_HEADER + PAGE_MAX_TRX_ID + page,
+				       autoinc, mtr);
+		}
 	}
 }
 

storage/innobase/page/page0page.cc

@@ -488,6 +488,22 @@ page_create_zip(
 	is_spatial = index ? dict_index_is_spatial(index)
 			   : page_comp_info->type & DICT_SPATIAL;
 
+	/* PAGE_MAX_TRX_ID or PAGE_ROOT_AUTO_INC are always 0 for
+	temporary tables. */
+	ut_ad(!dict_table_is_temporary(index->table) || max_trx_id == 0);
+	/* In secondary indexes and the change buffer, PAGE_MAX_TRX_ID
+	must be zero on non-leaf pages. max_trx_id can be 0 when the
+	index consists of an empty root (leaf) page. */
+	ut_ad(max_trx_id == 0
+	      || level == 0
+	      || !dict_index_is_sec_or_ibuf(index)
+	      || dict_table_is_temporary(index->table));
+	/* In the clustered index, PAGE_ROOT_AUTOINC or
+	PAGE_MAX_TRX_ID must be 0 on other pages than the root. */
+	ut_ad(level == 0 || max_trx_id == 0
+	      || !dict_index_is_sec_or_ibuf(index)
+	      || dict_table_is_temporary(index->table));
+
 	page = page_create_low(block, TRUE, is_spatial);
 	mach_write_to_2(PAGE_HEADER + PAGE_LEVEL + page, level);
 	mach_write_to_8(PAGE_HEADER + PAGE_MAX_TRX_ID + page, max_trx_id);
@@ -521,8 +537,8 @@ page_create_empty(
 	dict_index_t*	index,	/*!< in: the index of the page */
 	mtr_t*		mtr)	/*!< in/out: mini-transaction */
 {
-	trx_id_t	max_trx_id = 0;
-	const page_t*	page	= buf_block_get_frame(block);
+	trx_id_t	max_trx_id;
+	page_t*		page	= buf_block_get_frame(block);
 	page_zip_des_t*	page_zip= buf_block_get_page_zip(block);
 
 	ut_ad(fil_page_index_page_check(page));
@@ -536,6 +552,11 @@ page_create_empty(
 	    && page_is_leaf(page)) {
 		max_trx_id = page_get_max_trx_id(page);
 		ut_ad(max_trx_id);
+	} else if (page_is_root(page)) {
+		/* Preserve PAGE_ROOT_AUTO_INC. */
+		max_trx_id = page_get_max_trx_id(page);
+	} else {
+		max_trx_id = 0;
 	}
 
 	if (page_zip) {
@@ -547,8 +568,8 @@ page_create_empty(
 			    dict_index_is_spatial(index));
 
 		if (max_trx_id) {
-			page_update_max_trx_id(
-				block, page_zip, max_trx_id, mtr);
+			mlog_write_ull(PAGE_HEADER + PAGE_MAX_TRX_ID + page,
+				       max_trx_id, mtr);
 		}
 	}
 }

storage/innobase/page/page0zip.cc

@@ -4821,13 +4821,6 @@ page_zip_copy_recs(
 		ut_a(dict_index_is_clust(index));
 	}
 
-	/* The PAGE_MAX_TRX_ID must be set on leaf pages of secondary
-	indexes.  It does not matter on other pages. */
-	ut_a(dict_index_is_clust(index)
-	     || dict_table_is_temporary(index->table)
-	     || !page_is_leaf(src)
-	     || page_get_max_trx_id(src));
-
 	UNIV_MEM_ASSERT_W(page, UNIV_PAGE_SIZE);
 	UNIV_MEM_ASSERT_W(page_zip->data, page_zip_get_size(page_zip));
 	UNIV_MEM_ASSERT_RW(src, UNIV_PAGE_SIZE);
@@ -4849,6 +4842,19 @@ page_zip_copy_recs(
 	memcpy(PAGE_DATA + page_zip->data, PAGE_DATA + src_zip->data,
 	       page_zip_get_size(page_zip) - PAGE_DATA);
 
+	if (dict_index_is_clust(index)) {
+		/* Reset the PAGE_ROOT_AUTO_INC field when copying
+		from a root page. */
+		memset(PAGE_HEADER + PAGE_ROOT_AUTO_INC + page, 0, 8);
+		memset(PAGE_HEADER + PAGE_ROOT_AUTO_INC + page_zip->data,
+		       0, 8);
+	} else {
+		/* The PAGE_MAX_TRX_ID must be nonzero on leaf pages
+		of secondary indexes, and 0 on others. */
+		ut_ad(dict_table_is_temporary(index->table)
+		      || !page_is_leaf(src) == !page_get_max_trx_id(src));
+	}
+
 	/* Copy all fields of src_zip to page_zip, except the pointer
 	to the compressed data page. */
 	{