Add a new field to the WT_CURSOR_BTREE structure so we can pass back a

reference to the modify function's allocated update structure, avoids a
potential data copy when changing the user's cursor to point to internal
data.  Closes #1070.

4 files changed, 28 insertions, 9 deletions

diff --git a/src/btree/bt_cursor.c b/src/btree/bt_cursor.c
index d942c12f421..da2ef171414 100644
--- a/src/btree/bt_cursor.c
+++ b/src/btree/bt_cursor.c
@@ -681,15 +681,16 @@ retry:	WT_RET(__cursor_func_init(cbt, 1));
 err:	if (ret == WT_RESTART)
 		goto retry;
 
-	/* If successful, point the cursor at internal copies of the data. */
-	if (ret == 0) {
-		if (!WT_DATA_IN_ITEM(&cursor->key))
-			WT_TRET(__wt_buf_set(session, &cursor->key,
-			    cursor->key.data, cursor->key.size));
-		if (!WT_DATA_IN_ITEM(&cursor->value))
-			WT_TRET(__wt_buf_set(session, &cursor->value,
-			    cursor->value.data, cursor->value.size));
-	}
+	/*
+	 * If successful, point the cursor at internal copies of the data.  We
+	 * could shuffle memory in the cursor so the key/value pair are in local
+	 * buffer memory, but that's a data copy.  We don't want to do another
+	 * search (and we might get a different update structure if we race).
+	 * To make this work, we add a field to the btree cursor to pass back a
+	 * pointer to the modify function's allocated update structure.
+	 */
+	if (ret == 0)
+		WT_TRET(__wt_kv_return(session, cbt, cbt->modify_update));
 
 	if (ret != 0)
 		WT_TRET(__cursor_error_resolve(cbt));
diff --git a/src/btree/col_modify.c b/src/btree/col_modify.c
index 41ce37a0130..e2e3adbd714 100644
--- a/src/btree/col_modify.c
+++ b/src/btree/col_modify.c
@@ -86,6 +86,9 @@ __wt_col_modify(WT_SESSION_IMPL *session, WT_CURSOR_BTREE *cbt,
 		WT_ERR(__wt_txn_modify(session, upd));
 		logged = 1;
 
+		/* Avoid a data copy in WT_CURSOR.update. */
+		cbt->modify_update = upd;
+
 		/*
 		 * Point the new WT_UPDATE item to the next element in the list.
 		 * If we get it right, the serialization function lock acts as
@@ -135,6 +138,9 @@ __wt_col_modify(WT_SESSION_IMPL *session, WT_CURSOR_BTREE *cbt,
 			    __wt_update_alloc(session, value, &upd, &upd_size));
 			WT_ERR(__wt_txn_modify(session, upd));
 			logged = 1;
+
+			/* Avoid a data copy in WT_CURSOR.update. */
+			cbt->modify_update = upd;
 		} else
 			upd_size = sizeof(WT_UPDATE) + upd->size;
 		ins->upd = upd;
diff --git a/src/btree/row_modify.c b/src/btree/row_modify.c
index c088fabe53a..03772e317b4 100644
--- a/src/btree/row_modify.c
+++ b/src/btree/row_modify.c
@@ -66,6 +66,9 @@ __wt_row_modify(WT_SESSION_IMPL *session, WT_CURSOR_BTREE *cbt,
 			    __wt_update_alloc(session, value, &upd, &upd_size));
 			WT_ERR(__wt_txn_modify(session, upd));
 			logged = 1;
+
+			/* Avoid WT_CURSOR.update data copy. */
+			cbt->modify_update = upd;
 		} else {
 			upd_size = sizeof(WT_UPDATE) + upd->size;
 			/*
@@ -132,6 +135,9 @@ __wt_row_modify(WT_SESSION_IMPL *session, WT_CURSOR_BTREE *cbt,
 			    __wt_update_alloc(session, value, &upd, &upd_size));
 			WT_ERR(__wt_txn_modify(session, upd));
 			logged = 1;
+
+			/* Avoid WT_CURSOR.update data copy. */
+			cbt->modify_update = upd;
 		} else
 			upd_size = sizeof(WT_UPDATE) + upd->size;
 		ins->upd = upd;
diff --git a/src/include/cursor.h b/src/include/cursor.h
index 7d59bd88f39..90314f0af61 100644
--- a/src/include/cursor.h
+++ b/src/include/cursor.h
@@ -158,6 +158,12 @@ struct __wt_cursor_btree {
 	WT_ITEM tmp;
 
 	/*
+	 * The update structure allocated by the row- and column-store modify
+	 * functions, used to avoid a data copy in the WT_CURSOR.update call.
+	 */
+	WT_UPDATE *modify_update;
+
+	/*
 	 * Fixed-length column-store items are a single byte, and it's simpler
 	 * and cheaper to allocate the space for it now than keep checking to
 	 * see if we need to grow the buffer.