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SHOW EXPLAIN UPDATE/DELETE

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- Introduce "Query Plan Footprints" (abbrev. QPFs)
  QPF is a part of query plan that is 
  1. sufficient to produce EXPLAIN output,
  2. can be used to produce EXPLAIN output even after its subquery/union
     was executed and deleted
  3. is cheap to save so that we can always save query plans

- This patch doesn't fully address #2, we make/save strings for 
  a number of EXPLAIN's columns.  This will be fixed.
This commit is contained in:
Sergey Petrunya
2013-06-17 11:59:38 +04:00
parent 9718b9763d
commit 03691a7771
12 changed files with 1466 additions and 15 deletions
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8
sql/sql_parse.cc
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@ -4811,7 +4811,15 @@ static bool execute_sqlcom_select(THD *thd, TABLE_LIST *all_tables)
if (!(result= new select_send()))
return 1; /* purecov: inspected */
thd->send_explain_fields(result);
thd->lex->query_plan_footprint= new QPF_query;
res= mysql_explain_union(thd, &thd->lex->unit, result);
thd->lex->query_plan_footprint->print_explain(result, thd->lex->describe);
//psergey-todo: here, produce the EXPLAIN output.
// mysql_explain_union() itself is only responsible for calling
// optimize() for all parts of the query.
/*
The code which prints the extended description is not robust
against malformed queries, so skip it if we have an error.