Reduce the size of btr_search_t from 13 machine words to 7. This

structure is reserved for every index in the data dictionary cache.
(Bug #20877)

We could shrink the structure further to three 32-bit words or two
64-bit words by turning the remaining fields to bit-fields.
Unfortunately, the fields are not protected by any mutex, and thus we
would better keep each field aligned to a machine word.

btr_search_t, buf_block_t: Rename "ulint side" to "ibool left_side".
Remove BTR_SEARCH_LEFT_SIDE and BTR_SEARCH_RIGHT_SIDE, and also rename
some local variables and function parameters from "ulint side" to
"ibool left_side".

btr_search_t: Remove the unused fields last_search, n_direction, direction,
and modify_clock.  Remove the unused constants BTR_SEA_NO_DIRECTION,
BTR_SEA_LEFT, BTR_SEA_RIGHT, and BTR_SEA_SAME_REC.

btr_search_t: Remove magic_n unless #defined UNIV_DEBUG.  Turn an assertion
about the magic number into a debug assertion.

btr/btr0sea.c

@@ -74,7 +74,7 @@ btr_search_build_page_hash_index(
 	ulint		n_fields,/* in: hash this many full fields */
 	ulint		n_bytes,/* in: hash this many bytes from the next
 				field */
-	ulint		side);	/* in: hash for searches from this side */
+	ibool		left_side);/* in: hash for searches from left side? */
 
 /*********************************************************************
 This function should be called before reserving any btr search mutex, if
@@ -157,10 +157,10 @@ btr_search_info_create(
 
 	info = mem_heap_alloc(heap, sizeof(btr_search_t));
 
+#ifdef UNIV_DEBUG
 	info->magic_n = BTR_SEARCH_MAGIC_N;
+#endif /* UNIV_DEBUG */
 
-	info->last_search = NULL;
-	info->n_direction = 0;
 	info->root_guess = NULL;
 
 	info->hash_analysis = 0;
@@ -179,7 +179,7 @@ btr_search_info_create(
 	info->n_fields = 1;
 	info->n_bytes = 0;
 
-	info->side = BTR_SEARCH_LEFT_SIDE;
+	info->left_side = TRUE;
 
 	return(info);
 }
@@ -224,7 +224,7 @@ btr_search_info_update_hash(
 	hash prefix */
 
 	if (info->n_fields >= n_unique && cursor->up_match >= n_unique) {
-
+increment_potential:
 		info->n_hash_potential++;
 
 		return;
@@ -233,8 +233,7 @@ btr_search_info_update_hash(
 	cmp = ut_pair_cmp(info->n_fields, info->n_bytes,
 			  cursor->low_match, cursor->low_bytes);
 
-	if ((info->side == BTR_SEARCH_LEFT_SIDE && cmp <= 0)
-	    || (info->side == BTR_SEARCH_RIGHT_SIDE && cmp > 0)) {
+	if (info->left_side ? cmp <= 0 : cmp > 0) {
 
 		goto set_new_recomm;
 	}
@@ -242,16 +241,11 @@ btr_search_info_update_hash(
 	cmp = ut_pair_cmp(info->n_fields, info->n_bytes,
 			  cursor->up_match, cursor->up_bytes);
 
-	if ((info->side == BTR_SEARCH_LEFT_SIDE && cmp > 0)
-	    || (info->side == BTR_SEARCH_RIGHT_SIDE && cmp <= 0)) {
+	if (info->left_side ? cmp <= 0 : cmp > 0) {
 
-		goto set_new_recomm;
+		goto increment_potential;
 	}
 
-	info->n_hash_potential++;
-
-	return;
-
 set_new_recomm:
 	/* We have to set a new recommendation; skip the hash analysis
 	for a while to avoid unnecessary CPU time usage when there is no
@@ -269,7 +263,7 @@ btr_search_info_update_hash(
 		info->n_fields = 1;
 		info->n_bytes = 0;
 
-		info->side = BTR_SEARCH_LEFT_SIDE;
+		info->left_side = TRUE;
 
 	} else if (cmp > 0) {
 		info->n_hash_potential = 1;
@@ -288,7 +282,7 @@ btr_search_info_update_hash(
 			info->n_bytes = cursor->low_bytes + 1;
 		}
 
-		info->side = BTR_SEARCH_LEFT_SIDE;
+		info->left_side = TRUE;
 	} else {
 		info->n_hash_potential = 1;
 
@@ -306,7 +300,7 @@ btr_search_info_update_hash(
 			info->n_bytes = cursor->up_bytes + 1;
 		}
 
-		info->side = BTR_SEARCH_RIGHT_SIDE;
+		info->left_side = FALSE;
 	}
 }
 
@@ -336,18 +330,18 @@ btr_search_update_block_hash_info(
 	info->last_hash_succ = FALSE;
 
 	ut_a(block->magic_n == BUF_BLOCK_MAGIC_N);
-	ut_a(info->magic_n == BTR_SEARCH_MAGIC_N);
+	ut_ad(info->magic_n == BTR_SEARCH_MAGIC_N);
 
 	if ((block->n_hash_helps > 0)
 	    && (info->n_hash_potential > 0)
 	    && (block->n_fields == info->n_fields)
 	    && (block->n_bytes == info->n_bytes)
-	    && (block->side == info->side)) {
+	    && (block->left_side == info->left_side)) {
 
 		if ((block->is_hashed)
 		    && (block->curr_n_fields == info->n_fields)
 		    && (block->curr_n_bytes == info->n_bytes)
-		    && (block->curr_side == info->side)) {
+		    && (block->curr_left_side == info->left_side)) {
 
 			/* The search would presumably have succeeded using
 			the hash index */
@@ -360,7 +354,7 @@ btr_search_update_block_hash_info(
 		block->n_hash_helps = 1;
 		block->n_fields = info->n_fields;
 		block->n_bytes = info->n_bytes;
-		block->side = info->side;
+		block->left_side = info->left_side;
 	}
 
 #ifdef UNIV_DEBUG
@@ -378,7 +372,7 @@ btr_search_update_block_hash_info(
 			> 2 * page_get_n_recs(block->frame))
 		    || (block->n_fields != block->curr_n_fields)
 		    || (block->n_bytes != block->curr_n_bytes)
-		    || (block->side != block->curr_side)) {
+		    || (block->left_side != block->curr_left_side)) {
 
 			/* Build a new hash index on the page */
 
@@ -422,7 +416,7 @@ btr_search_update_hash_ref(
 	    && (info->n_hash_potential > 0)
 	    && (block->curr_n_fields == info->n_fields)
 	    && (block->curr_n_bytes == info->n_bytes)
-	    && (block->curr_side == info->side)) {
+	    && (block->curr_left_side == info->left_side)) {
 		mem_heap_t*	heap		= NULL;
 		ulint		offsets_[REC_OFFS_NORMAL_SIZE];
 		*offsets_ = (sizeof offsets_) / sizeof *offsets_;
@@ -512,7 +506,7 @@ btr_search_info_update_slow(
 		params = mem_alloc(3 * sizeof(ulint));
 		params[0] = block->n_fields;
 		params[1] = block->n_bytes;
-		params[2] = block->side;
+		params[2] = block->left_side;
 
 		/* Make sure the compiler cannot deduce the values and do
 		optimizations */
@@ -1102,7 +1096,7 @@ btr_search_build_page_hash_index(
 	ulint		n_fields,/* in: hash this many full fields */
 	ulint		n_bytes,/* in: hash this many bytes from the next
 				field */
-	ulint		side)	/* in: hash for searches from this side */
+	ibool		left_side)/* in: hash for searches from left side? */
 {
 	hash_table_t*	table;
 	buf_block_t*	block;
@@ -1136,7 +1130,7 @@ btr_search_build_page_hash_index(
 
 	if (block->is_hashed && ((block->curr_n_fields != n_fields)
 				 || (block->curr_n_bytes != n_bytes)
-				 || (block->curr_side != side))) {
+				 || (block->curr_left_side != left_side))) {
 
 		rw_lock_s_unlock(&btr_search_latch);
 
@@ -1191,7 +1185,7 @@ btr_search_build_page_hash_index(
 
 	fold = rec_fold(rec, offsets, n_fields, n_bytes, tree_id);
 
-	if (side == BTR_SEARCH_LEFT_SIDE) {
+	if (left_side) {
 
 		folds[n_cached] = fold;
 		recs[n_cached] = rec;
@@ -1203,7 +1197,7 @@ btr_search_build_page_hash_index(
 
 		if (page_rec_is_supremum(next_rec)) {
 
-			if (side == BTR_SEARCH_RIGHT_SIDE) {
+			if (!left_side) {
 
 				folds[n_cached] = fold;
 				recs[n_cached] = rec;
@@ -1221,7 +1215,7 @@ btr_search_build_page_hash_index(
 		if (fold != next_fold) {
 			/* Insert an entry into the hash index */
 
-			if (side == BTR_SEARCH_LEFT_SIDE) {
+			if (left_side) {
 
 				folds[n_cached] = next_fold;
 				recs[n_cached] = next_rec;
@@ -1243,7 +1237,7 @@ btr_search_build_page_hash_index(
 
 	if (block->is_hashed && ((block->curr_n_fields != n_fields)
 				 || (block->curr_n_bytes != n_bytes)
-				 || (block->curr_side != side))) {
+				 || (block->curr_left_side != left_side))) {
 		goto exit_func;
 	}
 
@@ -1252,7 +1246,7 @@ btr_search_build_page_hash_index(
 
 	block->curr_n_fields = n_fields;
 	block->curr_n_bytes = n_bytes;
-	block->curr_side = side;
+	block->curr_left_side = left_side;
 	block->index = index;
 
 	for (i = 0; i < n_cached; i++) {
@@ -1291,7 +1285,7 @@ btr_search_move_or_delete_hash_entries(
 	buf_block_t*	new_block;
 	ulint		n_fields;
 	ulint		n_bytes;
-	ulint		side;
+	ibool		left_side;
 
 	block = buf_block_align(page);
 	new_block = buf_block_align(new_page);
@@ -1319,22 +1313,23 @@ btr_search_move_or_delete_hash_entries(
 
 		n_fields = block->curr_n_fields;
 		n_bytes = block->curr_n_bytes;
-		side = block->curr_side;
+		left_side = block->curr_left_side;
 
 		new_block->n_fields = block->curr_n_fields;
 		new_block->n_bytes = block->curr_n_bytes;
-		new_block->side = block->curr_side;
+		new_block->left_side = left_side;
 
 		rw_lock_s_unlock(&btr_search_latch);
 
 		ut_a(n_fields + n_bytes > 0);
 
 		btr_search_build_page_hash_index(index, new_page, n_fields,
-						 n_bytes, side);
+						 n_bytes, left_side);
+#if 1 /* TODO: safe to remove? */
 		ut_a(n_fields == block->curr_n_fields);
 		ut_a(n_bytes == block->curr_n_bytes);
-		ut_a(side == block->curr_side);
-
+		ut_a(left_side == block->curr_left_side);
+#endif
 		return;
 	}
 
@@ -1428,7 +1423,7 @@ btr_search_update_hash_node_on_insert(
 	if ((cursor->flag == BTR_CUR_HASH)
 	    && (cursor->n_fields == block->curr_n_fields)
 	    && (cursor->n_bytes == block->curr_n_bytes)
-	    && (block->curr_side == BTR_SEARCH_RIGHT_SIDE)) {
+	    && !block->curr_left_side) {
 
 		table = btr_search_sys->hash_index;
 
@@ -1465,7 +1460,7 @@ btr_search_update_hash_on_insert(
 	ulint		next_fold = 0; /* remove warning (??? bug ???) */
 	ulint		n_fields;
 	ulint		n_bytes;
-	ulint		side;
+	ibool		left_side;
 	ibool		locked		= FALSE;
 	mem_heap_t*	heap		= NULL;
 	ulint		offsets_[REC_OFFS_NORMAL_SIZE];
@@ -1495,7 +1490,7 @@ btr_search_update_hash_on_insert(
 
 	n_fields = block->curr_n_fields;
 	n_bytes = block->curr_n_bytes;
-	side = block->curr_side;
+	left_side = block->curr_left_side;
 
 	ins_rec = page_rec_get_next(rec);
 	next_rec = page_rec_get_next(ins_rec);
@@ -1516,7 +1511,7 @@ btr_search_update_hash_on_insert(
 					  n_fields + (n_bytes > 0), &heap);
 		fold = rec_fold(rec, offsets, n_fields, n_bytes, tree_id);
 	} else {
-		if (side == BTR_SEARCH_LEFT_SIDE) {
+		if (left_side) {
 
 			rw_lock_x_lock(&btr_search_latch);
 
@@ -1537,7 +1532,7 @@ btr_search_update_hash_on_insert(
 			locked = TRUE;
 		}
 
-		if (side == BTR_SEARCH_RIGHT_SIDE) {
+		if (!left_side) {
 			ha_insert_for_fold(table, fold, rec);
 		} else {
 			ha_insert_for_fold(table, ins_fold, ins_rec);
@@ -1547,7 +1542,7 @@ btr_search_update_hash_on_insert(
 check_next_rec:
 	if (page_rec_is_supremum(next_rec)) {
 
-		if (side == BTR_SEARCH_RIGHT_SIDE) {
+		if (!left_side) {
 
 			if (!locked) {
 				rw_lock_x_lock(&btr_search_latch);
@@ -1570,7 +1565,7 @@ btr_search_update_hash_on_insert(
 			locked = TRUE;
 		}
 
-		if (side == BTR_SEARCH_RIGHT_SIDE) {
+		if (!left_side) {
 
 			ha_insert_for_fold(table, ins_fold, ins_rec);
 			/*
@@ -1680,7 +1675,7 @@ btr_search_validate(void)
 					(void*) page, (ulong) block->is_hashed,
 					(ulong) block->curr_n_fields,
 					(ulong) block->curr_n_bytes,
-					(ulong) block->curr_side);
+					(ulong) block->curr_left_side);
 
 				if (n_page_dumps < 20) {
 					buf_page_print(page);

buf/buf0buf.c

@@ -1583,7 +1583,7 @@ buf_page_init_for_backup_restore(
 	block->is_hashed	= FALSE;
 	block->n_fields		= 1;
 	block->n_bytes		= 0;
-	block->side		= BTR_SEARCH_LEFT_SIDE;
+	block->left_side	= TRUE;
 
 	block->file_page_was_freed = FALSE;
 }
@@ -1650,7 +1650,7 @@ buf_page_init(
 	block->is_hashed	= FALSE;
 	block->n_fields		= 1;
 	block->n_bytes		= 0;
-	block->side		= BTR_SEARCH_LEFT_SIDE;
+	block->left_side	= TRUE;
 
 	block->file_page_was_freed = FALSE;
 }

include/btr0sea.h

@@ -134,48 +134,34 @@ btr_search_validate(void);
 /*======================*/
 				/* out: TRUE if ok */
 
-/* Search info directions */
-#define BTR_SEA_NO_DIRECTION	1
-#define BTR_SEA_LEFT		2
-#define BTR_SEA_RIGHT		3
-#define BTR_SEA_SAME_REC	4
-
 /* The search info struct in an index */
 
 struct btr_search_struct{
-	ulint	magic_n;	/* magic number */
-	/* The following 4 fields are currently not used: */
-	rec_t*	last_search;	/* pointer to the lower limit record of the
-				previous search; NULL if not known */
-	ulint	n_direction;	/* number of consecutive searches in the
-				same direction */
-	ulint	direction;	/* BTR_SEA_NO_DIRECTION, BTR_SEA_LEFT,
-				BTR_SEA_RIGHT, BTR_SEA_SAME_REC,
-				or BTR_SEA_SAME_PAGE */
-	dulint	modify_clock;	/* value of modify clock at the time
-				last_search was stored */
-	/*----------------------*/
-	/* The following 4 fields are not protected by any latch: */
+	/* The following fields are not protected by any latch.
+	Unfortunately, this means that they must be aligned to
+	the machine word, i.e., they cannot be turned into bit-fields. */
 	page_t*	root_guess;	/* the root page frame when it was last time
 				fetched, or NULL */
-	ulint	hash_analysis;	/* when this exceeds a certain value, the
-				hash analysis starts; this is reset if no
+	ulint	hash_analysis;	/* when this exceeds BTR_SEARCH_HASH_ANALYSIS,
+				the hash analysis starts; this is reset if no
 				success noticed */
 	ibool	last_hash_succ;	/* TRUE if the last search would have
 				succeeded, or did succeed, using the hash
 				index; NOTE that the value here is not exact:
 				it is not calculated for every search, and the
 				calculation itself is not always accurate! */
-	ulint	n_hash_potential;/* number of consecutive searches which would
-				have succeeded, or did succeed, using the hash
-				index */
+	ulint	n_hash_potential;
+				/* number of consecutive searches
+				which would have succeeded, or did succeed,
+				using the hash index;
+				the range is 0 .. BTR_SEARCH_BUILD_LIMIT + 5 */
 	/*----------------------*/
 	ulint	n_fields;	/* recommended prefix length for hash search:
 				number of full fields */
 	ulint	n_bytes;	/* recommended prefix: number of bytes in
-				an incomplete field */
-	ulint	side;		/* BTR_SEARCH_LEFT_SIDE or
-				BTR_SEARCH_RIGHT_SIDE, depending on whether
+				an incomplete field;
+				cf. BTR_PAGE_MAX_REC_SIZE */
+	ibool	left_side;	/* TRUE or FALSE, depending on whether
 				the leftmost record of several records with
 				the same prefix should be indexed in the
 				hash index */
@@ -188,10 +174,12 @@ struct btr_search_struct{
 				far */
 	ulint	n_searches;	/* number of searches */
 #endif /* UNIV_SEARCH_PERF_STAT */
+#ifdef UNIV_DEBUG
+	ulint	magic_n;	/* magic number */
+# define BTR_SEARCH_MAGIC_N	1112765
+#endif /* UNIV_DEBUG */
 };
 
-#define BTR_SEARCH_MAGIC_N	1112765
-
 /* The hash index system */
 
 typedef struct btr_search_sys_struct	btr_search_sys_t;
@@ -229,9 +217,6 @@ is no hope in building a hash index. */
 
 #define BTR_SEARCH_HASH_ANALYSIS	17
 
-#define BTR_SEARCH_LEFT_SIDE	1
-#define BTR_SEARCH_RIGHT_SIDE	2
-
 /* Limit of consecutive searches for trying a search shortcut on the search
 pattern */
 

include/buf0buf.h

@@ -825,8 +825,7 @@ struct buf_block_struct{
 					search: number of full fields */
 	ulint		n_bytes;	/* recommended prefix: number of bytes
 					in an incomplete field */
-	ulint		side;		/* BTR_SEARCH_LEFT_SIDE or
-					BTR_SEARCH_RIGHT_SIDE, depending on
+	ibool		left_side;	/* TRUE or FALSE, depending on
 					whether the leftmost record of several
 					records with the same prefix should be
 					indexed in the hash index */
@@ -851,9 +850,7 @@ struct buf_block_struct{
 	ulint		curr_n_fields;	/* prefix length for hash indexing:
 					number of full fields */
 	ulint		curr_n_bytes;	/* number of bytes in hash indexing */
-	ulint		curr_side;	/* BTR_SEARCH_LEFT_SIDE or
-					BTR_SEARCH_RIGHT_SIDE in hash
-					indexing */
+	ibool		curr_left_side;	/* TRUE or FALSE in hash indexing */
 	dict_index_t*	index;		/* Index for which the adaptive
 					hash index has been created. */
 	/* 6. Debug fields */