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set @tmp_opt_switch= @@optimizer_switch;
set optimizer_switch='index_merge_sort_intersection=on';
set optimizer_trace='enabled=on';
create table t0 (a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t1 (a int, b int, c int, filler char(100),
key(a), key(b), key(c));
insert into t1 select
A.a * B.a*10 + C.a*100,
A.a * B.a*10 + C.a*100,
A.a,
'filler'
from t0 A, t0 B, t0 C;
This should use union:
explain select * from t1 where a=1 or b=1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge a,b a,b 5,5 NULL 2 Using union(a,b); Using where
select * from information_schema.OPTIMIZER_TRACE;
QUERY TRACE MISSING_BYTES_BEYOND_MAX_MEM_SIZE INSUFFICIENT_PRIVILEGES
explain select * from t1 where a=1 or b=1 {
"steps": [
{
"join_preparation": {
"select_id": 1,
"steps": [
{
"expanded_query": "select t1.a AS a,t1.b AS b,t1.c AS c,t1.filler AS filler from t1 where t1.a = 1 or t1.b = 1"
}
]
}
},
{
"join_optimization": {
"select_id": 1,
"steps": [
{
"condition_processing": {
"condition": "WHERE",
"original_condition": "t1.a = 1 or t1.b = 1",
"steps": [
{
"transformation": "equality_propagation",
"resulting_condition": "multiple equal(1, t1.a) or multiple equal(1, t1.b)"
},
{
"transformation": "constant_propagation",
"resulting_condition": "multiple equal(1, t1.a) or multiple equal(1, t1.b)"
},
{
"transformation": "trivial_condition_removal",
"resulting_condition": "multiple equal(1, t1.a) or multiple equal(1, t1.b)"
}
]
}
},
{
"table_dependencies": [
{
"table": "t1",
"row_may_be_null": false,
"map_bit": 0,
"depends_on_map_bits": []
}
]
},
{
"ref_optimizer_key_uses": []
},
{
"rows_estimation": [
{
"table": "t1",
"range_analysis": {
"table_scan": {
"rows": 1000,
"cost": 231.5878906
},
"potential_range_indexes": [
{
"index": "a",
"usable": true,
"key_parts": ["a"]
},
{
"index": "b",
"usable": true,
"key_parts": ["b"]
},
{
"index": "c",
"usable": false,
"cause": "not applicable"
}
],
"setup_range_conditions": [],
"analyzing_range_alternatives": {
"range_scan_alternatives": [],
"analyzing_roworder_intersect": {
"cause": "too few roworder scans"
},
"analyzing_sort_intersect": {},
"analyzing_index_merge_union": [
{
"indexes_to_merge": [
{
"range_scan_alternatives": [
{
"index": "a",
"ranges": ["(1) <= (a) <= (1)"],
"rowid_ordered": true,
"using_mrr": false,
"index_only": true,
"rows": 1,
"cost": 0.345585794,
"chosen": true
}
],
"index_to_merge": "a",
"cumulated_cost": 0.345585794
},
{
"range_scan_alternatives": [
{
"index": "b",
"ranges": ["(1) <= (b) <= (1)"],
"rowid_ordered": true,
"using_mrr": false,
"index_only": true,
"rows": 1,
"cost": 0.345585794,
"chosen": true
}
],
"index_to_merge": "b",
"cumulated_cost": 0.691171589
}
],
"cost_of_reading_ranges": 0.691171589,
"use_roworder_union": true,
"cause": "always cheaper than non roworder retrieval",
"analyzing_roworder_scans": [
{
"type": "range_scan",
"index": "a",
"rows": 1,
"ranges": ["(1) <= (a) <= (1)"],
"analyzing_roworder_intersect": {
"cause": "too few roworder scans"
}
},
{
"type": "range_scan",
"index": "b",
"rows": 1,
"ranges": ["(1) <= (b) <= (1)"],
"analyzing_roworder_intersect": {
"cause": "too few roworder scans"
}
}
],
"index_roworder_union_cost": 2.484903732,
"members": 2,
"chosen": true
}
]
},
"group_index_range": {
"chosen": false,
"cause": "no group by or distinct"
},
"chosen_range_access_summary": {
"range_access_plan": {
"type": "index_roworder_union",
"union_of": [
{
"type": "range_scan",
"index": "a",
"rows": 1,
"ranges": ["(1) <= (a) <= (1)"]
},
{
"type": "range_scan",
"index": "b",
"rows": 1,
"ranges": ["(1) <= (b) <= (1)"]
}
]
},
"rows_for_plan": 2,
"cost_for_plan": 2.484903732,
"chosen": true
}
}
},
{
"selectivity_for_indexes": [],
"selectivity_for_columns": [],
"cond_selectivity": 0.002
}
]
},
{
"considered_execution_plans": [
{
"plan_prefix": [],
"get_costs_for_tables": [
{
"best_access_path": {
"table": "t1",
"considered_access_paths": [
{
"access_type": "index_merge",
"resulting_rows": 2,
"cost": 2.484903732,
"chosen": true
}
],
"chosen_access_method": {
"type": "index_merge",
"records": 2,
"cost": 2.484903732,
"uses_join_buffering": false
}
}
}
]
},
{
"plan_prefix": [],
"table": "t1",
"rows_for_plan": 2,
"cost_for_plan": 2.884903732
}
]
},
{
"best_join_order": ["t1"]
},
{
"substitute_best_equal": {
"condition": "WHERE",
"resulting_condition": "t1.a = 1 or t1.b = 1"
}
},
{
"attaching_conditions_to_tables": {
"attached_conditions_computation": [],
"attached_conditions_summary": [
{
"table": "t1",
"attached": "t1.a = 1 or t1.b = 1"
}
]
}
}
]
}
}
]
} 0 0
drop table t0,t1;
set optimizer_trace="enabled=off";
set @@optimizer_switch= @tmp_opt_switch;
# More tests added index_merge access
create table t1
(
/* Field names reflect value(rowid) distribution, st=STairs, swt= SaWTooth */
st_a int not null default 0,
swt1a int not null default 0,
swt2a int not null default 0,
st_b int not null default 0,
swt1b int not null default 0,
swt2b int not null default 0,
/* fields/keys for row retrieval tests */
key1 int,
key2 int,
key3 int,
key4 int,
/* make rows much bigger then keys */
filler1 char (200),
filler2 char (200),
filler3 char (200),
filler4 char (200),
filler5 char (200),
filler6 char (200),
/* order of keys is important */
key sta_swt12a(st_a,swt1a,swt2a),
key sta_swt1a(st_a,swt1a),
key sta_swt2a(st_a,swt2a),
key sta_swt21a(st_a,swt2a,swt1a),
key st_a(st_a),
key stb_swt1a_2b(st_b,swt1b,swt2a),
key stb_swt1b(st_b,swt1b),
key st_b(st_b),
key(key1),
key(key2),
key(key3),
key(key4)
) ;
create table t0 as select * from t1;
# Printing of many insert into t0 values (....) disabled.
alter table t1 disable keys;
# Printing of many insert into t1 select .... from t0 disabled.
# Printing of many insert into t1 (...) values (....) disabled.
alter table t1 enable keys;
insert into t1 (key1, key2, key3, key4, filler1) values (100, 100, -1, -1, 'key1-key2');
insert into t1 (key1, key2, key3, key4, filler1) values (-1, -1, 100, 100, 'key4-key3');
set optimizer_trace='enabled=on';
# 3-way ROR-intersection
explain select key1,key2,key3 from t1 where key1=100 and key2=100 and key3=100;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge key1,key2,key3 key1,key2,key3 5,5,5 NULL 2 Using intersect(key1,key2,key3); Using where; Using index
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.analyzing_range_alternatives')) AS JS from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
{
"range_scan_alternatives":
[
{
"index": "key1",
"ranges":
["(100) <= (key1) <= (100)"],
"rowid_ordered": true,
"using_mrr": false,
"index_only": false,
"rows": 2243,
"cost": 2700.058937,
"chosen": true
},
{
"index": "key2",
"ranges":
["(100) <= (key2) <= (100)"],
"rowid_ordered": true,
"using_mrr": false,
"index_only": false,
"rows": 2243,
"cost": 2700.058937,
"chosen": false,
"cause": "cost"
},
{
"index": "key3",
"ranges":
["(100) <= (key3) <= (100)"],
"rowid_ordered": true,
"using_mrr": false,
"index_only": false,
"rows": 2243,
"cost": 2700.058937,
"chosen": false,
"cause": "cost"
}
],
"analyzing_roworder_intersect":
{
"intersecting_indexes":
[
{
"index": "key1",
"index_scan_cost": 10.31393703,
"cumulated_index_scan_cost": 10.31393703,
"disk_sweep_cost": 1923.144061,
"cumulative_total_cost": 1933.457998,
"usable": true,
"matching_rows_now": 2243,
"intersect_covering_with_this_index": false,
"chosen": true
},
{
"index": "key2",
"index_scan_cost": 10.31393703,
"cumulated_index_scan_cost": 20.62787405,
"disk_sweep_cost": 84.51771758,
"cumulative_total_cost": 105.1455916,
"usable": true,
"matching_rows_now": 77.6360508,
"intersect_covering_with_this_index": false,
"chosen": true
},
{
"index": "key3",
"index_scan_cost": 10.31393703,
"cumulated_index_scan_cost": 30.94181108,
"disk_sweep_cost": 0,
"cumulative_total_cost": 30.94181108,
"usable": true,
"matching_rows_now": 2.687185191,
"intersect_covering_with_this_index": true,
"chosen": true
}
],
"clustered_pk":
{
"clustered_pk_added_to_intersect": false,
"cause": "no clustered pk index"
},
"rows": 2,
"cost": 30.94181108,
"covering": true,
"chosen": true
},
"analyzing_index_merge_union":
[]
}
]
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.chosen_range_access_summary')) AS JS from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
{
"range_access_plan":
{
"type": "index_roworder_intersect",
"rows": 2,
"cost": 30.94181108,
"covering": true,
"clustered_pk_scan": false,
"intersect_of":
[
{
"type": "range_scan",
"index": "key1",
"rows": 2243,
"ranges":
["(100) <= (key1) <= (100)"]
},
{
"type": "range_scan",
"index": "key2",
"rows": 2243,
"ranges":
["(100) <= (key2) <= (100)"]
},
{
"type": "range_scan",
"index": "key3",
"rows": 2243,
"ranges":
["(100) <= (key3) <= (100)"]
}
]
},
"rows_for_plan": 2,
"cost_for_plan": 30.94181108,
"chosen": true
}
]
# ROR-union(ROR-intersection, ROR-range)
explain select key1,key2,key3,key4 from t1 where key1=100 and key2=100 or key3=100 and key4=100;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge key1,key2,key3,key4 key1,key2,key3,key4 5,5,5,5 NULL 154 Using union(intersect(key1,key2),intersect(key3,key4)); Using where
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.analyzing_range_alternatives')) AS JS from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
{
"range_scan_alternatives":
[],
"analyzing_roworder_intersect":
{
"cause": "too few roworder scans"
},
"analyzing_index_merge_union":
[
{
"indexes_to_merge":
[
{
"range_scan_alternatives":
[
{
"index": "key1",
"ranges":
["(100) <= (key1) <= (100)"],
"rowid_ordered": true,
"using_mrr": false,
"index_only": true,
"rows": 2243,
"cost": 457.058937,
"chosen": true
},
{
"index": "key2",
"ranges":
["(100) <= (key2) <= (100)"],
"rowid_ordered": true,
"using_mrr": false,
"index_only": true,
"rows": 2243,
"cost": 457.058937,
"chosen": false,
"cause": "cost"
}
],
"index_to_merge": "key1",
"cumulated_cost": 457.058937
},
{
"range_scan_alternatives":
[
{
"index": "key3",
"ranges":
["(100) <= (key3) <= (100)"],
"rowid_ordered": true,
"using_mrr": false,
"index_only": true,
"rows": 2243,
"cost": 457.058937,
"chosen": true
},
{
"index": "key4",
"ranges":
["(100) <= (key4) <= (100)"],
"rowid_ordered": true,
"using_mrr": false,
"index_only": true,
"rows": 2243,
"cost": 457.058937,
"chosen": false,
"cause": "cost"
}
],
"index_to_merge": "key3",
"cumulated_cost": 914.1178741
}
],
"cost_of_reading_ranges": 914.1178741,
"use_roworder_union": true,
"cause": "always cheaper than non roworder retrieval",
"analyzing_roworder_scans":
[
{
"type": "range_scan",
"index": "key1",
"rows": 2243,
"ranges":
["(100) <= (key1) <= (100)"],
"analyzing_roworder_intersect":
{
"intersecting_indexes":
[
{
"index": "key1",
"index_scan_cost": 10.31393703,
"cumulated_index_scan_cost": 10.31393703,
"disk_sweep_cost": 1923.144061,
"cumulative_total_cost": 1933.457998,
"usable": true,
"matching_rows_now": 2243,
"intersect_covering_with_this_index": false,
"chosen": true
},
{
"index": "key2",
"index_scan_cost": 10.31393703,
"cumulated_index_scan_cost": 20.62787405,
"disk_sweep_cost": 84.51771758,
"cumulative_total_cost": 105.1455916,
"usable": true,
"matching_rows_now": 77.6360508,
"intersect_covering_with_this_index": false,
"chosen": true
}
],
"clustered_pk":
{
"clustered_pk_added_to_intersect": false,
"cause": "no clustered pk index"
},
"rows": 77,
"cost": 105.1455916,
"covering": false,
"chosen": true
}
},
{
"type": "range_scan",
"index": "key3",
"rows": 2243,
"ranges":
["(100) <= (key3) <= (100)"],
"analyzing_roworder_intersect":
{
"intersecting_indexes":
[
{
"index": "key3",
"index_scan_cost": 10.31393703,
"cumulated_index_scan_cost": 10.31393703,
"disk_sweep_cost": 1923.144061,
"cumulative_total_cost": 1933.457998,
"usable": true,
"matching_rows_now": 2243,
"intersect_covering_with_this_index": false,
"chosen": true
},
{
"index": "key4",
"index_scan_cost": 10.31393703,
"cumulated_index_scan_cost": 20.62787405,
"disk_sweep_cost": 84.51771758,
"cumulative_total_cost": 105.1455916,
"usable": true,
"matching_rows_now": 77.6360508,
"intersect_covering_with_this_index": false,
"chosen": true
}
],
"clustered_pk":
{
"clustered_pk_added_to_intersect": false,
"cause": "no clustered pk index"
},
"rows": 77,
"cost": 105.1455916,
"covering": false,
"chosen": true
}
}
],
"index_roworder_union_cost": 194.9771115,
"members": 2,
"chosen": true
}
]
}
]
select JSON_DETAILED(JSON_EXTRACT(trace, '$**.chosen_range_access_summary')) AS JS from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
JS
[
{
"range_access_plan":
{
"type": "index_roworder_union",
"union_of":
[
{
"type": "index_roworder_intersect",
"rows": 77,
"cost": 105.1455916,
"covering": false,
"clustered_pk_scan": false,
"intersect_of":
[
{
"type": "range_scan",
"index": "key1",
"rows": 2243,
"ranges":
["(100) <= (key1) <= (100)"]
},
{
"type": "range_scan",
"index": "key2",
"rows": 2243,
"ranges":
["(100) <= (key2) <= (100)"]
}
]
},
{
"type": "index_roworder_intersect",
"rows": 77,
"cost": 105.1455916,
"covering": false,
"clustered_pk_scan": false,
"intersect_of":
[
{
"type": "range_scan",
"index": "key3",
"rows": 2243,
"ranges":
["(100) <= (key3) <= (100)"]
},
{
"type": "range_scan",
"index": "key4",
"rows": 2243,
"ranges":
["(100) <= (key4) <= (100)"]
}
]
}
]
},
"rows_for_plan": 154,
"cost_for_plan": 194.9771115,
"chosen": true
}
]
drop table t0,t1;
set optimizer_trace="enabled=off";