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Fix for bug lp:834492

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Analysis:
In the test query semi-join merges the inner-most subquery
into the outer subquery, and the optimization of the merged
subquery finds some new index access methods. Later the
IN-EXISTS transformation is applied to the unmerged subquery.
Since the optimizer is instructed to not consider
materialization, it reoptimizes the plan in-place to take into
account the new IN-EXISTS conditions. Just before reoptimization
JOIN::choose_subquery_plan resets the query plan, which also
resets the access methods found during the semi-join merge.
Then reoptimization discovers there are no new access methods,
but it leaves the query plan in its reset state. Later semi-join
crashes because it assumes these access methods are present.

Solution:
When reoptimizing in-place, reset the query plan only after new
access methods were discovered. If no new access methods were
discovered, leave the current plan as it was.
This commit is contained in:
unknown
2011-09-01 23:53:12 +03:00
parent 11ebbabb08
commit ea8aa32909
5 changed files with 94 additions and 11 deletions
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18
sql/sql_select.cc
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@@ -21546,6 +21546,19 @@ void JOIN::save_query_plan(Join_plan_state *save_to)
}
/**
Reset a query execution plan so that it can be reoptimized in-place.
*/
void JOIN::reset_query_plan()
{
for (uint i= 0; i < table_count; i++)
{
join_tab[i].keyuse= NULL;
join_tab[i].checked_keys.clear_all();
}
}
/**
Restore a query execution plan previously saved by the caller.
@@ -21579,7 +21592,8 @@ void JOIN::restore_query_plan(Join_plan_state *restore_from)
@param added_where An extra conjunct to the WHERE clause to reoptimize with
@param join_tables The set of tables to reoptimize
@param save_to If != NULL, save here the state of the current query plan
@param save_to If != NULL, save here the state of the current query plan,
otherwise reuse the existing query plan structures.
@notes
Given a query plan that was already optimized taking into account some WHERE
@@ -21623,6 +21637,8 @@ JOIN::reoptimize(Item *added_where, table_map join_tables,
if (save_to)
save_query_plan(save_to);
else
reset_query_plan();
if (!keyuse.buffer &&
my_init_dynamic_array(&keyuse, sizeof(KEYUSE), 20, 64))