Moved the function trace_plan_prefix to the optimizer trace file

Also added comments for trace_plan_prefix and the class Json_writer_temp_disable

1 files changed, 34 insertions, 0 deletions

diff --git a/sql/opt_trace.cc b/sql/opt_trace.cc
index c80037ba864..7c82ba829bc 100644
--- a/sql/opt_trace.cc
+++ b/sql/opt_trace.cc
@@ -413,6 +413,12 @@ size_t Opt_trace_context::remaining_mem_size()
   return max_mem_size;
 }
 
+/*
+  Disable tracing for children if the current trace is already present.
+  Currently only one trace is stored and there is no mechanism
+  to restore traces, so disabling tracing for children is the best option.
+*/
+
 bool Opt_trace_context::disable_tracing_if_required()
 {
   if (current_trace)
@@ -631,6 +637,34 @@ void add_table_scan_values_to_trace(THD *thd, JOIN_TAB *tab)
            .add("cost", tab->read_time);
 }
 
+
+/*
+  @brief
+    Add the tables inside a partial join to the optimizer trace
+
+  @param join                join handler
+  @param idx                 length of the partial QEP in 'join->positions'
+  @table_map                 map of all non-const tables of the join
+
+  @note
+    This function is used during best_access_path to print the tables
+    inside the partial join that were considered doing the cost based
+    analysis of the various join orders.
+*/
+
+void trace_plan_prefix(JOIN *join, uint idx, table_map join_tables)
+{
+  THD *const thd= join->thd;
+  Json_writer_array plan_prefix(thd, "plan_prefix");
+  for (uint i= 0; i < idx; i++)
+  {
+    TABLE_LIST *const tr= join->positions[i].table->tab_list;
+    if (!(tr->map & join_tables))
+      plan_prefix.add_table_name(join->positions[i].table);
+  }
+}
+
+
 /*
   Print the join order of all the tables for top level select.