MDEV-18233 Moving the hash_node_t to improve locality of reference

When performing a hash search via HASH_SEARCH we first look at a key of a node
and then at its pointer to the next node in chain. If we have those in one cache
line instead of a two we reduce memory reads.

I found dict_table_t, fil_space_t and buf_page_t suitable for such improvement.

storage/innobase/include/buf0buf.h

@@ -1443,6 +1443,9 @@ struct buf_page_t{
 					by buf_pool->mutex. */
 	ib_uint32_t	offset;		/*!< page number; also protected
 					by buf_pool->mutex. */
+	buf_page_t*	hash;		/*!< node used in chaining to
+					buf_pool->page_hash or
+					buf_pool->zip_hash */
 	/** count of how manyfold this block is currently bufferfixed */
 #ifdef PAGE_ATOMIC_REF_COUNT
 	ib_uint32_t	buf_fix_count;
@@ -1489,9 +1492,6 @@ struct buf_page_t{
 					zip.data == NULL means an active
 					buf_pool->watch */
 #ifndef UNIV_HOTBACKUP
-	buf_page_t*	hash;		/*!< node used in chaining to
-					buf_pool->page_hash or
-					buf_pool->zip_hash */
 #ifdef UNIV_DEBUG
 	ibool		in_page_hash;	/*!< TRUE if in buf_pool->page_hash */
 	ibool		in_zip_hash;	/*!< TRUE if in buf_pool->zip_hash */

storage/innobase/include/dict0mem.h

@@ -926,8 +926,10 @@ struct dict_table_t{
 
 
 	table_id_t	id;	/*!< id of the table */
+	hash_node_t	id_hash; /*!< hash chain node */
 	mem_heap_t*	heap;	/*!< memory heap */
 	char*		name;	/*!< table name */
+	hash_node_t	name_hash; /*!< hash chain node */
 	const char*	dir_path_of_temp_table;/*!< NULL or the directory path
 				where a TEMPORARY table that was explicitly
 				created by a user should be placed if
@@ -983,8 +985,6 @@ struct dict_table_t{
 				dictionary information and
 				MySQL FRM information mismatch. */
 #ifndef UNIV_HOTBACKUP
-	hash_node_t	name_hash; /*!< hash chain node */
-	hash_node_t	id_hash; /*!< hash chain node */
 	UT_LIST_BASE_NODE_T(dict_index_t)
 			indexes; /*!< list of indexes of the table */
 

storage/innobase/include/fil0fil.h

@@ -245,7 +245,9 @@ struct fil_node_t {
 struct fil_space_t {
 	char*		name;	/*!< space name = the path to the first file in
 				it */
+	hash_node_t	name_hash;/*!< hash chain the name_hash table */
 	ulint		id;	/*!< space id */
+	hash_node_t	hash;	/*!< hash chain node */
 	ib_int64_t	tablespace_version;
 				/*!< in DISCARD/IMPORT this timestamp
 				is used to check if we should ignore
@@ -292,8 +294,6 @@ struct fil_space_t {
 				trying to read a block.
 				Dropping of the tablespace is forbidden
 				if this is positive */
-	hash_node_t	hash;	/*!< hash chain node */
-	hash_node_t	name_hash;/*!< hash chain the name_hash table */
 #ifndef UNIV_HOTBACKUP
 	rw_lock_t	latch;	/*!< latch protecting the file space storage
 				allocation */

storage/xtradb/include/buf0buf.h

@@ -1477,6 +1477,9 @@ struct buf_page_t{
 
 	ib_uint32_t	space;		/*!< tablespace id. */
 	ib_uint32_t	offset;		/*!< page number. */
+	buf_page_t*	hash;		/*!< node used in chaining to
+					buf_pool->page_hash or
+					buf_pool->zip_hash */
 	/** count of how manyfold this block is currently bufferfixed */
 #ifdef PAGE_ATOMIC_REF_COUNT
 	ib_uint32_t	buf_fix_count;
@@ -1530,9 +1533,6 @@ struct buf_page_t{
 					zip.data == NULL means an active
 					buf_pool->watch */
 #ifndef UNIV_HOTBACKUP
-	buf_page_t*	hash;		/*!< node used in chaining to
-					buf_pool->page_hash or
-					buf_pool->zip_hash */
 #ifdef UNIV_DEBUG
 	ibool		in_page_hash;	/*!< TRUE if in buf_pool->page_hash */
 	ibool		in_zip_hash;	/*!< TRUE if in buf_pool->zip_hash */

storage/xtradb/include/dict0mem.h

@@ -937,8 +937,10 @@ struct dict_table_t{
 
 
 	table_id_t	id;	/*!< id of the table */
+	hash_node_t	id_hash; /*!< hash chain node */
 	mem_heap_t*	heap;	/*!< memory heap */
 	char*		name;	/*!< table name */
+	hash_node_t	name_hash; /*!< hash chain node */
 	const char*	dir_path_of_temp_table;/*!< NULL or the directory path
 				where a TEMPORARY table that was explicitly
 				created by a user should be placed if
@@ -994,8 +996,6 @@ struct dict_table_t{
 				dictionary information and
 				MySQL FRM information mismatch. */
 #ifndef UNIV_HOTBACKUP
-	hash_node_t	name_hash; /*!< hash chain node */
-	hash_node_t	id_hash; /*!< hash chain node */
 	UT_LIST_BASE_NODE_T(dict_index_t)
 			indexes; /*!< list of indexes of the table */
 

storage/xtradb/include/fil0fil.h

@@ -238,7 +238,9 @@ struct fil_node_t {
 struct fil_space_t {
 	char*		name;	/*!< space name = the path to the first file in
 				it */
+	hash_node_t	name_hash;/*!< hash chain the name_hash table */
 	ulint		id;	/*!< space id */
+	hash_node_t	hash;	/*!< hash chain node */
 	ib_int64_t	tablespace_version;
 				/*!< in DISCARD/IMPORT this timestamp
 				is used to check if we should ignore
@@ -285,8 +287,6 @@ struct fil_space_t {
 				trying to read a block.
 				Dropping of the tablespace is forbidden
 				if this is positive */
-	hash_node_t	hash;	/*!< hash chain node */
-	hash_node_t	name_hash;/*!< hash chain the name_hash table */
 #ifndef UNIV_HOTBACKUP
 	prio_rw_lock_t	latch;	/*!< latch protecting the file space storage
 				allocation */