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Change cost for REF to take into account cost for 1 extra key read_next

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The main difference in code path between EQ_REF and REF is that for
REF we have to do an extra read_next on the index to check that there
is no more matching rows.

Before this patch we added a preference of EQ_REF by ensuring that REF
would always estimate to find at least 2 rows.

This patch adds the cost of the extra key read_next to REF access and
removes the code that limited REF to at least 2 rows. For some queries
this can have a big effect as the total estimated rows will be halved
for each REF table with 1 rows.

multi_range cost calculations are also changed to take into account
the difference between EQ_REF and REF.

The effect of the patch to the test suite:
- About 80 test case changed
- Almost all changes where for EXPLAIN where estimated rows for REF
  where changed from 2 to 1.
- A few test cases using explain extended had a change of 'filtered'.
  This is because of the estimated rows are now closer to the
  calculated selectivity.
- A very few test had a change of table order.
  This is because the change of estimated rows from 2 to 1 or the small
  cost change for REF
  (main.subselect_sj_jcl6, main.group_by, main.dervied_cond_pushdown,
  main.distinct, main.join_nested, main.order_by, main.join_cache)
- No key statistics and the estimated rows are now smaller which cased
  estimated filtering to be lower.
  (main.subselect_sj_mat)
- The number of total rows are halved.
  (main.derived_cond_pushdown)
- Plans with 1 row changed to use RANGE instead of REF.
  (main.group_min_max)
- ALL changed to REF
  (main.key_diff)
- Key changed from ref + index_only to PRIMARY key for InnoDB, as
  OPTIMIZER_ROW_LOOKUP_COST + OPTIMIZER_ROW_NEXT_FIND_COST is smaller than
  OPTIMIZER_KEY_LOOKUP_COST + OPTIMIZER_KEY_NEXT_FIND_COST.
  (main.join_outer_innodb)
- Cost changes printouts
  (main.opt_trace*)
- Result order change
  (innodb_gis.rtree)
This commit is contained in:
Monty
2022-12-27 14:49:27 +02:00
parent b5df077e85
commit 3fa99f0c0e
81 changed files with 765 additions and 740 deletions
Download Patch File Download Diff File Expand all files Collapse all files

42
mysql-test/main/opt_trace_index_merge.result
View File

@ -113,12 +113,12 @@ explain select * from t1 where a=1 or b=1 {
"using_mrr": false,
"index_only": true,
"rows": 1,
"cost": 0.001388369,
"cost": 0.001478954,
"chosen": true
}
],
"index_to_merge": "a",
"cumulated_cost": 0.001388369
"cumulated_cost": 0.001478954
},
{
"range_scan_alternatives": [
@ -129,15 +129,15 @@ explain select * from t1 where a=1 or b=1 {
"using_mrr": false,
"index_only": true,
"rows": 1,
"cost": 0.001388369,
"cost": 0.001478954,
"chosen": true
}
],
"index_to_merge": "b",
"cumulated_cost": 0.002776738
"cumulated_cost": 0.002957908
}
],
"cost_of_reading_ranges": 0.002776738,
"cost_of_reading_ranges": 0.002957908,
"use_roworder_union": true,
"cause": "always cheaper than non roworder retrieval",
"analyzing_roworder_scans": [
@ -160,7 +160,7 @@ explain select * from t1 where a=1 or b=1 {
}
}
],
"index_roworder_union_cost": 0.005004612,
"index_roworder_union_cost": 0.005185782,
"members": 2,
"chosen": true
}
@ -189,7 +189,7 @@ explain select * from t1 where a=1 or b=1 {
]
},
"rows_for_plan": 2,
"cost_for_plan": 0.005004612,
"cost_for_plan": 0.005185782,
"chosen": true
}
}
@ -222,7 +222,7 @@ explain select * from t1 where a=1 or b=1 {
"rows": 2,
"rows_after_filter": 2,
"rows_out": 2,
"cost": 0.005004612,
"cost": 0.005185782,
"chosen": true
}
],
@ -230,7 +230,7 @@ explain select * from t1 where a=1 or b=1 {
"type": "index_merge",
"rows_read": 2,
"rows_out": 2,
"cost": 0.005004612,
"cost": 0.005185782,
"uses_join_buffering": false
}
}
@ -241,14 +241,14 @@ explain select * from t1 where a=1 or b=1 {
"plan_prefix": "",
"table": "t1",
"rows_for_plan": 2,
"cost_for_plan": 0.005004612
"cost_for_plan": 0.005185782
}
]
},
{
"best_join_order": ["t1"],
"rows": 2,
"cost": 0.005004612
"cost": 0.005185782
},
{
"substitute_best_equal": {
@ -347,7 +347,7 @@ JSON_DETAILED(JSON_EXTRACT(trace, '$**.analyzing_range_alternatives'))
"using_mrr": false,
"index_only": false,
"rows": 2243,
"cost": 2.770260666,
"cost": 2.770351251,
"chosen": true
},
{
@ -358,7 +358,7 @@ JSON_DETAILED(JSON_EXTRACT(trace, '$**.analyzing_range_alternatives'))
"using_mrr": false,
"index_only": false,
"rows": 2243,
"cost": 2.770260666,
"cost": 2.770351251,
"chosen": false,
"cause": "cost"
},
@ -370,7 +370,7 @@ JSON_DETAILED(JSON_EXTRACT(trace, '$**.analyzing_range_alternatives'))
"using_mrr": false,
"index_only": false,
"rows": 2243,
"cost": 2.770260666,
"cost": 2.770351251,
"chosen": false,
"cause": "cost"
}
@ -492,7 +492,7 @@ JSON_DETAILED(JSON_EXTRACT(trace, '$**.analyzing_range_alternatives'))
"using_mrr": false,
"index_only": true,
"rows": 2243,
"cost": 0.312832109,
"cost": 0.312922694,
"chosen": true
},
{
@ -503,13 +503,13 @@ JSON_DETAILED(JSON_EXTRACT(trace, '$**.analyzing_range_alternatives'))
"using_mrr": false,
"index_only": true,
"rows": 2243,
"cost": 0.312832109,
"cost": 0.312922694,
"chosen": false,
"cause": "cost"
}
],
"index_to_merge": "key1",
"cumulated_cost": 0.312832109
"cumulated_cost": 0.312922694
},
{
"range_scan_alternatives":
@ -522,7 +522,7 @@ JSON_DETAILED(JSON_EXTRACT(trace, '$**.analyzing_range_alternatives'))
"using_mrr": false,
"index_only": true,
"rows": 2243,
"cost": 0.312832109,
"cost": 0.312922694,
"chosen": true
},
{
@ -533,16 +533,16 @@ JSON_DETAILED(JSON_EXTRACT(trace, '$**.analyzing_range_alternatives'))
"using_mrr": false,
"index_only": true,
"rows": 2243,
"cost": 0.312832109,
"cost": 0.312922694,
"chosen": false,
"cause": "cost"
}
],
"index_to_merge": "key3",
"cumulated_cost": 0.625664218
"cumulated_cost": 0.625845388
}
],
"cost_of_reading_ranges": 0.625664218,
"cost_of_reading_ranges": 0.625845388,
"use_roworder_union": true,
"cause": "always cheaper than non roworder retrieval",
"analyzing_roworder_scans":