branches/zip: Improve code locality in btr_cur_search_to_nth_level().

Make the variables rw_latch and buf_mode local in the for loop.
Initialize them at the beginning of each for loop round to reduce
register spilling on register-starved platforms such as the x86.  Move
the assignment of rw_latch and buf_mode from the end of the loop to
the beginning of the loop.  These parameters will only be needed in
the buf_page_get_gen() call at the start of the loop.

Remove the second (redundant) call to ibuf_should_try().

ibuf_should_try(): Now that the successful calls to this function will
be halved, halve the magic constant that ibuf_flush_count will be
compared to, accordingly.

rb://61 approved by Heikki over IM.

btr/btr0cur.c

@@ -318,10 +318,8 @@ btr_cur_search_to_nth_level(
 	ulint		low_bytes;
 	ulint		height;
 	ulint		savepoint;
-	ulint		rw_latch;
 	ulint		page_mode;
 	ulint		insert_planned;
-	ulint		buf_mode;
 	ulint		estimate;
 	ulint		ignore_sec_unique;
 	ulint		root_height = 0; /* remove warning */
@@ -429,8 +427,6 @@ btr_cur_search_to_nth_level(
 	low_bytes = 0;
 
 	height = ULINT_UNDEFINED;
-	rw_latch = RW_NO_LATCH;
-	buf_mode = BUF_GET;
 
 	/* We use these modified search modes on non-leaf levels of the
 	B-tree. These let us end up in the right B-tree leaf. In that leaf
@@ -459,9 +455,28 @@ btr_cur_search_to_nth_level(
 	for (;;) {
 		ulint		zip_size;
 		buf_block_t*	block;
-retry_page_get:
+		ulint		rw_latch;
+		ulint		buf_mode;
+
 		zip_size = dict_table_zip_size(index->table);
+		rw_latch = RW_NO_LATCH;
+		buf_mode = BUF_GET;
+
+		if (height == 0 && latch_mode <= BTR_MODIFY_LEAF) {
+
+			rw_latch = latch_mode;
+
+			if (insert_planned
+			    && ibuf_should_try(index, ignore_sec_unique)) {
+
+				/* Try insert to the insert buffer if the
+				page is not in the buffer pool */
+
+				buf_mode = BUF_GET_IF_IN_POOL;
+			}
+		}
 
+retry_page_get:
 		block = buf_page_get_gen(space, zip_size, page_no,
 					 rw_latch, guess, buf_mode,
 					 __FILE__, __LINE__, mtr);
@@ -473,9 +488,8 @@ retry_page_get:
 			ut_ad(insert_planned);
 			ut_ad(cursor->thr);
 
-			if (ibuf_should_try(index, ignore_sec_unique)
-			    && ibuf_insert(tuple, index, space, zip_size,
-					   page_no, cursor->thr)) {
+			if (ibuf_insert(tuple, index, space, zip_size,
+					page_no, cursor->thr)) {
 				/* Insertion to the insert buffer succeeded */
 				cursor->flag = BTR_CUR_INSERT_TO_IBUF;
 				if (UNIV_LIKELY_NULL(heap)) {
@@ -574,20 +588,6 @@ retry_page_get:
 
 		height--;
 
-		if ((height == 0) && (latch_mode <= BTR_MODIFY_LEAF)) {
-
-			rw_latch = latch_mode;
-
-			if (insert_planned
-			    && ibuf_should_try(index, ignore_sec_unique)) {
-
-				/* Try insert to the insert buffer if the
-				page is not in the buffer pool */
-
-				buf_mode = BUF_GET_IF_IN_POOL;
-			}
-		}
-
 		guess = NULL;
 
 		node_ptr = page_cur_get_rec(page_cursor);

include/ibuf0ibuf.ic

@@ -91,7 +91,7 @@ ibuf_should_try(
 
 		ibuf_flush_count++;
 
-		if (ibuf_flush_count % 8 == 0) {
+		if (ibuf_flush_count % 4 == 0) {
 
 			buf_LRU_try_free_flushed_blocks();
 		}