Implement UNIV_BTR_AVOID_COPY, an optimization of page splits.

storage/innodb_plugin/ChangeLog

+2010-04-20	The InnoDB Team
+
+	* btr/btr0btr.c, include/univ.i:
+	Implement UNIV_BTR_AVOID_COPY, for avoiding writes when a B-tree
+	node is split at the first or last record.
+
 2010-04-15	The InnoDB Team
 
 	* trx/trx0rec.c:

storage/innodb_plugin/btr/btr0btr.c

@@ -2015,7 +2015,17 @@ btr_page_split_and_insert(
 	}
 
 	/* 5. Move then the records to the new page */
-	if (direction == FSP_DOWN) {
+	if (direction == FSP_DOWN
+#ifdef UNIV_BTR_AVOID_COPY
+	    && page_rec_is_supremum(move_limit)) {
+		/* Instead of moving all records, make the new page
+		the empty page. */
+
+		left_block = block;
+		right_block = new_block;
+	} else if (direction == FSP_DOWN
+#endif /* UNIV_BTR_AVOID_COPY */
+		   ) {
 		/*		fputs("Split left\n", stderr); */
 
 		if (0
@@ -2058,6 +2068,14 @@ btr_page_split_and_insert(
 		right_block = block;
 
 		lock_update_split_left(right_block, left_block);
+#ifdef UNIV_BTR_AVOID_COPY
+	} else if (!split_rec) {
+		/* Instead of moving all records, make the new page
+		the empty page. */
+
+		left_block = new_block;
+		right_block = block;
+#endif /* UNIV_BTR_AVOID_COPY */
 	} else {
 		/*		fputs("Split right\n", stderr); */
 

storage/innodb_plugin/include/univ.i

@@ -205,6 +205,10 @@ operations (very slow); also UNIV_DEBUG must be defined */
 						adaptive hash index */
 #define UNIV_SRV_PRINT_LATCH_WAITS		/* enable diagnostic output
 						in sync0sync.c */
+#define UNIV_BTR_AVOID_COPY			/* when splitting B-tree nodes,
+						do not move any records when
+						all the records would
+						be moved */
 #define UNIV_BTR_PRINT				/* enable functions for
 						printing B-trees */
 #define UNIV_ZIP_DEBUG				/* extensive consistency checks