find_all_keys: add an assert, remove current_thd

Filesort temporarily changes read_set to be tmp_set and marks only
fields needed for filesort. Add an assert to ensure that it doesn't
overwrite the old value of tmp_set, that is that read_set was *not*
already tmp_set when filesort was invoked.

Fix sql_update.cc that was was doing exactly that - changing read_set to
tmp_set, configuring tmp_set for keyread, and then invoking filesort.

sql/filesort.cc

@@ -747,8 +747,7 @@ static ha_rows find_all_keys(THD *thd, Sort_param *param, SQL_SELECT *select,
                     DBUG_SET("+d,ha_rnd_init_fail"););
     if (file->ha_rnd_init_with_error(1))
       DBUG_RETURN(HA_POS_ERROR);
-    file->extra_opt(HA_EXTRA_CACHE,
-		    current_thd->variables.read_buff_size);
+    file->extra_opt(HA_EXTRA_CACHE, thd->variables.read_buff_size);
   }
 
   /* Remember original bitmaps */
@@ -757,6 +756,7 @@ static ha_rows find_all_keys(THD *thd, Sort_param *param, SQL_SELECT *select,
   save_vcol_set=  sort_form->vcol_set;
 
   /* Set up temporary column read map for columns used by sort */
+  DBUG_ASSERT(save_read_set != &sort_form->tmp_set);
   bitmap_clear_all(&sort_form->tmp_set);
   sort_form->column_bitmaps_set(&sort_form->tmp_set, &sort_form->tmp_set, 
                                 &sort_form->tmp_set);

sql/sql_update.cc

@@ -534,16 +534,9 @@ int mysql_update(THD *thd,
     /*
       We can't update table directly;  We must first search after all
       matching rows before updating the table!
-    */
-    MY_BITMAP *save_read_set= table->read_set;
-    MY_BITMAP *save_write_set= table->write_set;
-
-    if (query_plan.index < MAX_KEY && old_covering_keys.is_set(query_plan.index))
-      table->prepare_for_keyread(query_plan.index);
-    else
-      table->use_all_columns();
 
-    /* note: We avoid sorting if we sort on the used index */
+      note: We avoid sorting if we sort on the used index
+    */
     if (query_plan.using_filesort)
     {
       /*
@@ -569,6 +562,14 @@ int mysql_update(THD *thd,
     }
     else
     {
+      MY_BITMAP *save_read_set= table->read_set;
+      MY_BITMAP *save_write_set= table->write_set;
+
+      if (query_plan.index < MAX_KEY && old_covering_keys.is_set(query_plan.index))
+        table->prepare_for_keyread(query_plan.index);
+      else
+        table->use_all_columns();
+
       /*
 	We are doing a search on a key that is updated. In this case
 	we go trough the matching rows, save a pointer to them and
@@ -681,10 +682,11 @@ int mysql_update(THD *thd,
       select->file=tempfile;			// Read row ptrs from this file
       if (error >= 0)
 	goto err;
-    }
+
       table->file->ha_end_keyread();
       table->column_bitmaps_set(save_read_set, save_write_set);
     }
+  }
 
   if (ignore)
     table->file->extra(HA_EXTRA_IGNORE_DUP_KEY);