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MDEV-35072: Assertion with optimizer_join_limit_pref_ratio and 1-table select

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Variant for 11.2+:

In recompute_join_cost_with_limit(), do not subtract the cost of checking
the WHERE:
   pos->records_read* WHERE_COST_THD(join->thd)

It is already included in pos->read_time.

Also added comments about difference between this fix and the pre-11.2
variant.
This commit is contained in:
Sergei Petrunia
2024-10-10 12:33:59 +03:00
parent 690f8a91f9
commit 66b8d32b75
3 changed files with 32 additions and 15 deletions
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14
sql/sql_select.cc
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@@ -11626,6 +11626,8 @@ double recompute_join_cost_with_limit(const JOIN *join, bool skip_sorting,
POSITION *pos= join->best_positions + join->const_tables;
/*
Generally, we assume that producing X% of output takes X% of the cost.
(Note: before 11.0, we subtracted COST_EPS here. In 11.0+, there's no need
to do this)
*/
double partial_join_cost= join->best_read * fraction;
@@ -11646,10 +11648,11 @@ double recompute_join_cost_with_limit(const JOIN *join, bool skip_sorting,
{
/*
Subtract the remainder of the first table's cost we had in
join->best_read:
join->best_read.
(Before 11.0, we also subtracted pos->records_read/TIME_FOR_COMPARE.
In 11.0+, that time is already included in pos->read_time)
*/
partial_join_cost -= pos->read_time*fraction;
partial_join_cost -= pos->records_read*fraction * WHERE_COST_THD(join->thd);
/* Add the cost of the new access method we've got: */
partial_join_cost= COST_ADD(partial_join_cost, *first_table_cost);
@@ -11666,12 +11669,7 @@ double recompute_join_cost_with_limit(const JOIN *join, bool skip_sorting,
table. Do the same for costs of checking the WHERE.
*/
double extra_first_table_cost= pos->read_time * (1.0 - fraction);
double extra_first_table_where= pos->records_read * (1.0 - fraction) *
WHERE_COST_THD(join->thd);
partial_join_cost= COST_ADD(partial_join_cost,
COST_ADD(extra_first_table_cost,
extra_first_table_where));
partial_join_cost= COST_ADD(partial_join_cost, extra_first_table_cost);
}
return partial_join_cost;
}