TEMPORARY PUSH: Changing all cost calculation to be given in ms10.7-selectivity-old

- Added tests/check_costs.pl, a tool to verify optimizer cost calculations.
  - Most costs has been found with this program. All steps to calculate
    the new costs are documented in Docs/optimizer.costs
- User optimizer_cost variables are given in usec (as individual
  costs can be very small). Internally they are stored in ms.
- Changed DISK_READ_COST (was DISK_SEEK_BASE_COST) from a hard disk cost
  (9 ms) to common SSD cost (400MB/sec).
- Changed the following handler functions to return IO_AND_CPU_COST.
  This makes it easy to apply different cost modifiers in ha_..time()
  functions for io and cpu costs.
  - scan_time()
  - rndpos_time()
  - keyread_time()
- Enhanched keyread_time() to calculate the full cost of reading of a set
  of keys with a given number of ranges and optionall number of blocks that
  need to be accessed.
- Removed read_time() as keyread_time() + rndpos_time() is the same thing.
- Added the following new optimizer_variables:
  - optimizer_scan_lookup_cost
  - optimizer_row_lookup_cost
  - optimizer_index_lookup_cost
  - optimizer_disk_read_cost
- Added include/my_tracker.h  ; Useful include file to quickly test costs
  of a function.
- Tuned sequence and heap engine costs (rest will be done in an updated
  commit)

1 files changed, 1 insertions, 1 deletions

diff --git a/sql/set_var.h b/sql/set_var.h
index 570703a8222..38a395adf0f 100644
--- a/sql/set_var.h
+++ b/sql/set_var.h
@@ -84,7 +84,7 @@ protected:
   typedef bool (*on_update_function)(sys_var *self, THD *thd, enum_var_type type);
 
   int flags;            ///< or'ed flag_enum values
-  const SHOW_TYPE show_val_type; ///< what value_ptr() returns for sql_show.cc
+  SHOW_TYPE show_val_type; ///< what value_ptr() returns for sql_show.cc
   PolyLock *guard;      ///< *second* lock that protects the variable
   ptrdiff_t offset;     ///< offset to the value from global_system_variables
   on_check_function on_check;