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Merge.

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Igor Babaev
2014-04-22 14:43:13 -07:00
parent ed93e55bac 3e0f63c18f
commit bcf16fa612
8 changed files with 49 additions and 26 deletions
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25
sql/opt_range.cc
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@ -13429,7 +13429,7 @@ SEL_ARG * get_index_range_tree(uint index, SEL_TREE* range_tree, PARAM *param,
DESCRIPTION
This method computes the access cost of a TRP_GROUP_MIN_MAX instance and
the number of rows returned. It updates this->read_cost and this->records.
the number of rows returned.
NOTES
The cost computation distinguishes several cases:
@ -13485,7 +13485,6 @@ void cost_group_min_max(TABLE* table, KEY *index_info, uint used_key_parts,
double p_overlap; /* Probability that a sub-group overlaps two blocks. */
double quick_prefix_selectivity;
double io_cost;
double cpu_cost= 0; /* TODO: CPU cost of index_read calls? */
DBUG_ENTER("cost_group_min_max");
table_records= table->stat_records();
@ -13533,11 +13532,25 @@ void cost_group_min_max(TABLE* table, KEY *index_info, uint used_key_parts,
(double) num_blocks;
/*
TODO: If there is no WHERE clause and no other expressions, there should be
no CPU cost. We leave it here to make this cost comparable to that of index
scan as computed in SQL_SELECT::test_quick_select().
CPU cost must be comparable to that of an index scan as computed
in SQL_SELECT::test_quick_select(). When the groups are small,
e.g. for a unique index, using index scan will be cheaper since it
reads the next record without having to re-position to it on every
group. To make the CPU cost reflect this, we estimate the CPU cost
as the sum of:
1. Cost for evaluating the condition (similarly as for index scan).
2. Cost for navigating the index structure (assuming a b-tree).
Note: We only add the cost for one comparision per block. For a
b-tree the number of comparisons will be larger.
TODO: This cost should be provided by the storage engine.
*/
cpu_cost= (double) num_groups / TIME_FOR_COMPARE;
const double tree_traversal_cost=
ceil(log(static_cast<double>(table_records))/
log(static_cast<double>(keys_per_block))) *
1/double(2*TIME_FOR_COMPARE);
const double cpu_cost= num_groups *
(tree_traversal_cost + 1/double(TIME_FOR_COMPARE));
*read_cost= io_cost + cpu_cost;
*records= num_groups;