diff --git a/Makefile b/Makefile
index 8380f1e..52eb2d1 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 CC=gcc
-CFLAGS=-Wall -O0 -g
+CFLAGS=-Wall -O2 -g
 LDFLAGS=-lm -lreadline
 
 all: makeidx openidx readidx
diff --git a/index.c b/index.c
index 5dad358..3b2f762 100644
--- a/index.c
+++ b/index.c
@@ -6,12 +6,7 @@
 #include "bitmap.h"
 #include <libgen.h>
 #include <linux/limits.h>
-
-#define BTREE_ERR_CANNOT_OPEN_FILE    -1
-#define BTREE_ERR_PAGE_SIZE_DIFFERENT -2
-
-#define BTREE_OPTIMIZE_RECORDS_MIN 10
-#define BTREE_OPTIMIZE_THRESHOLD   0.1
+#include <unistd.h>
 
 #define SWAP(type, x, y) do { type __tmp__; __tmp__ = y; y = x; x = __tmp__; } while (0)
 
@@ -193,6 +188,8 @@ int btree_init(btree_t *tree, char* filename, size_t d)
     tree->header.d         = d;
     tree->header.page_size = PAGE_SIZE;
     tree->header.root      = _btree_alloc(tree);
+    tree->header.records   = 0;
+    tree->header.changes   = 0;
 
     _btree_save_header(tree);
     
@@ -312,7 +309,7 @@ bool _btree_compensate_insert(btree_t *tree, btree_node_t *old, btree_entry_t *e
     if (siblings.left) {
         _btree_load_node(&other, tree, siblings.left);
         if (other.header.entries < 2*tree->header.d) {
-            _btree_node_insert_entry(&other, *entry);
+            _btree_node_insert_entry(old, *entry);
             _btree_rebalance(tree, &other, old, siblings.left_entry);
             return true;
         }
@@ -321,7 +318,7 @@ bool _btree_compensate_insert(btree_t *tree, btree_node_t *old, btree_entry_t *e
     if (siblings.right) {
         _btree_load_node(&other, tree, siblings.right);
         if (other.header.entries < 2*tree->header.d) {
-            _btree_node_insert_entry(&other, *entry);
+            _btree_node_insert_entry(old, *entry);
             _btree_rebalance(tree, old, &other, siblings.right_entry);
             return true;
         }
@@ -722,20 +719,24 @@ void _btree_optimize_page(btree_t* tree, tape_t* tmp, page_t page)
 
 void btree_optimize(btree_t *tree)
 {
-
-    char tmp[PATH_MAX + 4], old[PATH_MAX];
-    strcpy(old, tree->main->file->filename);
-    sprintf(tmp, "%s.tmp", old);
+    char tmp[PATH_MAX], path[PATH_MAX - 10], backup[PATH_MAX];
+    strcpy(path, tree->main->file->filename);
+    sprintf(tmp, "%s.tmp", path);
+    sprintf(backup, "%s.bckp", path);
 
     printfv(VERBOSITY_DEBUG, "[btree] Optimizing btree using temp file %s.\n", tmp);
 
-    tape_t *temp = tape_open(tmp, "wb+");
+    tape_t *temp = tape_open(tmp, "wb");
     _btree_optimize_page(tree, temp, tree->header.root);
     tape_close(temp);
     tape_close(tree->main);
 
-    remove(old);
-    rename(tmp, old);
+    printfv(VERBOSITY_DEBUG, "[btree] Renaming %s to %s.\n", path, backup);
+    rename(path, backup);
 
-    tree->main = tape_open(old, "rb+");
+    printfv(VERBOSITY_DEBUG, "[btree] Renaming %s to %s.\n", tmp, path);
+    if (rename(tmp, path) == 0) {
+        tree->main = tape_open(path, "rb+");
+        tree->header.changes = 0;
+    }
 }
diff --git a/index.h b/index.h
index 2a8dfbc..e2154df 100644
--- a/index.h
+++ b/index.h
@@ -18,6 +18,12 @@
 #define NODE_IS_ROOT 1
 #define NODE_IS_LEAF 2
 
+#define BTREE_ERR_CANNOT_OPEN_FILE    -1
+#define BTREE_ERR_PAGE_SIZE_DIFFERENT -2
+
+#define BTREE_OPTIMIZE_RECORDS_MIN 1000
+#define BTREE_OPTIMIZE_THRESHOLD   0.1
+
 typedef struct {
     size_t d;         /* 8 bytes long */
     size_t page_size; /* 8 bytes long */
diff --git a/io.c b/io.c
index 08e6c23..ec8af3b 100644
--- a/io.c
+++ b/io.c
@@ -21,6 +21,7 @@ file_t* file_open(const char* filename, const char* mode)
 
     printfv(VERBOSITY_VERY_VERBOSE, "[io] File %s opened in %s with page size %zu.\n", filename, mode, PAGE_SIZE);
     file_t* result = malloc(sizeof(file_t));
+    memset(result, 0, sizeof(file_t));
 
     result->file     = handle;
     result->filename = malloc(strlen(filename) + 1);