Improved speed of optimizer trace

- Added unlikely() to optimize for not having optimizer trace enabled
- Made THD::trace_started() inline
- Added 'if (trace_enabled())' around some potentially expensive code
  (not many found)
- Added ASSERT's to ensure we don't call expensive optimizer trace calls
  if optimizer trace is not enabled
- Added length to Json_writer functions to speed up buffer writes
  when optimizer trace is enabled.
- Changed LEX_CSTRING argument handling to not send full struct to writer
  function on_add_str() functions now trusts length arguments

1 files changed, 4 insertions, 1 deletions

diff --git a/sql/sql_test.cc b/sql/sql_test.cc
index 68d30d5fecb..a3506687a72 100644
--- a/sql/sql_test.cc
+++ b/sql/sql_test.cc
@@ -658,9 +658,12 @@ Memory allocated by threads:             %s\n",
 
 void print_keyuse_array_for_trace(THD *thd, DYNAMIC_ARRAY *keyuse_array)
 {
+  DBUG_ASSERT(thd->trace_started());
+
   Json_writer_object wrapper(thd);
   Json_writer_array trace_key_uses(thd, "ref_optimizer_key_uses");
-  for(uint i=0; i < keyuse_array->elements; i++)
+
+  for (uint i=0; i < keyuse_array->elements; i++)
   {
     KEYUSE *keyuse= (KEYUSE*)dynamic_array_ptr(keyuse_array, i);
     Json_writer_object keyuse_elem(thd);