Bug #17858679 TOO MANY TIMES OF MEMSET DECREASE

THE PERFORMANCE UNDER HEAVY INSERT
Problem:
	There are three memset call to allocate memory for system fields
in each insert.

Solution:
	Instead of calling it in 3 times, we can combine it into
one memset call. It will reduce the CPU usage under heavy insert.

	Approved by Marko rb-4916

storage/innobase/row/row0ins.c

@@ -151,35 +151,37 @@ row_ins_alloc_sys_fields(
 	ut_ad(row && table && heap);
 	ut_ad(dtuple_get_n_fields(row) == dict_table_get_n_cols(table));
 
-	/* 1. Allocate buffer for row id */
+	/* allocate buffer to hold the needed system created hidden columns. */
+	uint len = DATA_ROW_ID_LEN + DATA_TRX_ID_LEN + DATA_ROLL_PTR_LEN;
+	ptr = mem_heap_zalloc(heap, len);
 
+	/* 1. Populate row-id */
 	col = dict_table_get_sys_col(table, DATA_ROW_ID);
 
 	dfield = dtuple_get_nth_field(row, dict_col_get_no(col));
 
-	ptr = mem_heap_zalloc(heap, DATA_ROW_ID_LEN);
-
 	dfield_set_data(dfield, ptr, DATA_ROW_ID_LEN);
 
 	node->row_id_buf = ptr;
 
-	/* 3. Allocate buffer for trx id */
+	ptr += DATA_ROW_ID_LEN;
 
+	/* 2. Populate trx id */
 	col = dict_table_get_sys_col(table, DATA_TRX_ID);
 
 	dfield = dtuple_get_nth_field(row, dict_col_get_no(col));
-	ptr = mem_heap_zalloc(heap, DATA_TRX_ID_LEN);
 
 	dfield_set_data(dfield, ptr, DATA_TRX_ID_LEN);
 
 	node->trx_id_buf = ptr;
 
-	/* 4. Allocate buffer for roll ptr */
+	ptr += DATA_TRX_ID_LEN;
+
+	/* 3. Populate roll ptr */
 
 	col = dict_table_get_sys_col(table, DATA_ROLL_PTR);
 
 	dfield = dtuple_get_nth_field(row, dict_col_get_no(col));
-	ptr = mem_heap_zalloc(heap, DATA_ROLL_PTR_LEN);
 
 	dfield_set_data(dfield, ptr, DATA_ROLL_PTR_LEN);
 }