Adjust table_open_cache to avoid getting error 24 (too many open files)

MDEV--15609 engines/funcs.crash_manytables_number crashes with error 24
           (too many open files)
MDEV-10286  Adjustment of table_open_cache according to system limits
            does not work when open-files-limit option is provided

Fixed by adjusting tc_size downwards if there is not enough file
descriptors to use.

Other changes:
- Ensure that there is 30 (was 10) extra file descriptors for other usage
- Decrease TABLE_OPEN_CACHE_MIN to 200 as it's better to have a smaller
  table cache than getting error 24
- Increase minimum of max_connections and table_open_cache from 1 to 10
  as 1 is not usable for any real application, only for testing.

1 files changed, 10 insertions, 0 deletions

diff --git a/sql/set_var.h b/sql/set_var.h
index cf86ecf18fa..fe66eaff775 100644
--- a/sql/set_var.h
+++ b/sql/set_var.h
@@ -394,6 +394,16 @@ int sql_set_variables(THD *thd, List<set_var_base> *var_list, bool free);
     set_sys_var_value_origin(&VAR, sys_var::AUTO);      \
   } while(0)
 
+#define SYSVAR_AUTOSIZE_IF_CHANGED(VAR,VAL,TYPE)        \
+  do {                                                  \
+    TYPE tmp= (VAL);                                    \
+    if (VAR != tmp)                                     \
+    {                                                   \
+      VAR= (VAL);                                       \
+      set_sys_var_value_origin(&VAR, sys_var::AUTO);    \
+    }                                                   \
+  } while(0)
+
 void set_sys_var_value_origin(void *ptr, enum sys_var::where here);
 
 enum sys_var::where get_sys_var_value_origin(void *ptr);