For performance reasons we remove the ability in unique indexes on...

For performance reasons we remove the ability in unique indexes on autoincrements to remove the ability to insert key lower then the current autoincrement value.

mysql-test/r/archive.result

@@ -12367,6 +12367,7 @@ INSERT INTO t5 VALUES (NULL, "foo");
 INSERT INTO t5 VALUES (NULL, "foo");
 INSERT INTO t5 VALUES (32, "foo");
 INSERT INTO t5 VALUES (23, "foo");
+ERROR 23000: Can't write; duplicate key in table 't5'
 INSERT INTO t5 VALUES (NULL, "foo");
 INSERT INTO t5 VALUES (NULL, "foo");
 INSERT INTO t5 VALUES (3, "foo");
@@ -12380,7 +12381,6 @@ a	b
 4	foo
 5	foo
 32	foo
-23	foo
 33	foo
 34	foo
 35	foo

mysql-test/t/archive.test

@@ -1379,6 +1379,7 @@ INSERT INTO t5 VALUES (NULL, "foo");
 INSERT INTO t5 VALUES (NULL, "foo");
 INSERT INTO t5 VALUES (NULL, "foo");
 INSERT INTO t5 VALUES (32, "foo");
+--error 1022
 INSERT INTO t5 VALUES (23, "foo");
 INSERT INTO t5 VALUES (NULL, "foo");
 INSERT INTO t5 VALUES (NULL, "foo");

storage/archive/ha_archive.cc

@@ -784,23 +784,22 @@ int ha_archive::write_row(byte *buf)
     temp_auto= table->next_number_field->val_int();
 
     /*
-      Simple optimization to see if we fail for duplicate key immediatly
-      because we have just given out this value.
+      We don't support decremening auto_increment. They make the performance
+      just cry.
     */
-    if (temp_auto == share->archive_write.auto_increment && 
+    if (temp_auto <= share->archive_write.auto_increment && 
         mkey->flags & HA_NOSAME)
     {
       rc= HA_ERR_FOUND_DUPP_KEY;
       goto error;
     }
+#ifdef DEAD_CODE
     /*
       Bad news, this will cause a search for the unique value which is very 
       expensive since we will have to do a table scan which will lock up 
       all other writers during this period. This could perhaps be optimized 
       in the future.
     */
-    if (temp_auto < share->archive_write.auto_increment && 
-        mkey->flags & HA_NOSAME)
     {
       /* 
         First we create a buffer that we can use for reading rows, and can pass
@@ -838,6 +837,7 @@ int ha_archive::write_row(byte *buf)
         }
       }
     }
+#endif
     else
     {
       if (temp_auto > share->archive_write.auto_increment)