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MDEV-21932 A fast plan with ROR index-merge is ignored when
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           'index_merge_sort_union=off'

When index_merge_sort_union is set to 'off' and  index_merge_union is set
to 'on' then any evaluated index merge scan must consist only of ROR scans.
The cheapest out of such index merges must be chosen. This index merge
might not be the cheapest index merge.
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@igorbabaev @montywi
igorbabaev authored and montywi committed Mar 17, 2020
1 parent 1242eb3 commit a2d24de
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51 changes: 51 additions & 0 deletions mysql-test/main/index_merge_myisam.result
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Original file line number Diff line number Diff line change
Expand Up @@ -1728,3 +1728,54 @@ key1 key2 key3 key8
3 3 3 1021
set @@optimizer_switch= @optimizer_switch_save;
drop table t0;
create table t0 (a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
insert into t0 select a+10 from t0;
insert into t0 select a+20 from t0;
insert into t0 select a+40 from t0;
insert into t0 select a+80 from t0;
insert into t0 select a+160 from t0;
delete from t0 where a > 300;
create table t1 (
f1 int, f2 int, f3 int, f4 int,
primary key (f1), key (f3), key(f4)
) engine=myisam;
insert into t1 select a+100, a+100, a+100, a+100 from t0;
insert into t1 VALUES (9,0,2,6), (9930,0,0,NULL);
analyze table t1;
Table Op Msg_type Msg_text
test.t1 analyze status Engine-independent statistics collected
test.t1 analyze status OK
set optimizer_switch='index_merge_sort_union=off';
set optimizer_switch='index_merge_union=on';
explain select * from t1
where (( f3 = 1 or f1 = 7 ) and f1 < 10) or
(f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge PRIMARY,f3,f4 f3,PRIMARY,f3 5,4,5 NULL 3 Using union(f3,PRIMARY,f3); Using where
select * from t1
where (( f3 = 1 or f1 = 7 ) and f1 < 10) or
(f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
f1 f2 f3 f4
9 0 2 6
insert into t1 values (52,0,1,0),(53,0,1,0);
insert into t1 values (50,0,1,0),(51,0,1,0);
insert into t1 values (48,0,1,0),(49,0,1,0);
insert into t1 values (46,0,1,0),(47,0,1,0);
insert into t1 values (44,0,1,0),(45,0,1,0);
analyze table t1;
Table Op Msg_type Msg_text
test.t1 analyze status Engine-independent statistics collected
test.t1 analyze status OK
explain select * from t1
where (( f3 = 1 or f1 = 7 ) and f1 < 10) or
(f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index_merge PRIMARY,f3,f4 f3,PRIMARY,f3 5,4,5 NULL 13 Using union(f3,PRIMARY,f3); Using where
select * from t1
where (( f3 = 1 or f1 = 7 ) and f1 < 10) or
(f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
f1 f2 f3 f4
9 0 2 6
drop table t0,t1;
set optimizer_switch= @optimizer_switch_save;
41 changes: 41 additions & 0 deletions mysql-test/main/index_merge_myisam.test
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Original file line number Diff line number Diff line change
Expand Up @@ -271,3 +271,44 @@ explain select * from (select * from t0 where key1 = 3 or key2 =3) as Z where Z.
select * from (select * from t0 where key1 = 3 or key2 =3) as Z where Z.key8 > 5;
set @@optimizer_switch= @optimizer_switch_save;
drop table t0;

#
# MDEV-21932: ROR union with index_merge_sort_union=off
#
create table t0 (a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
insert into t0 select a+10 from t0;
insert into t0 select a+20 from t0;
insert into t0 select a+40 from t0;
insert into t0 select a+80 from t0;
insert into t0 select a+160 from t0;
delete from t0 where a > 300;
create table t1 (
f1 int, f2 int, f3 int, f4 int,
primary key (f1), key (f3), key(f4)
) engine=myisam;
insert into t1 select a+100, a+100, a+100, a+100 from t0;
insert into t1 VALUES (9,0,2,6), (9930,0,0,NULL);
analyze table t1;
set optimizer_switch='index_merge_sort_union=off';
set optimizer_switch='index_merge_union=on';
explain select * from t1
where (( f3 = 1 or f1 = 7 ) and f1 < 10) or
(f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
select * from t1
where (( f3 = 1 or f1 = 7 ) and f1 < 10) or
(f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
insert into t1 values (52,0,1,0),(53,0,1,0);
insert into t1 values (50,0,1,0),(51,0,1,0);
insert into t1 values (48,0,1,0),(49,0,1,0);
insert into t1 values (46,0,1,0),(47,0,1,0);
insert into t1 values (44,0,1,0),(45,0,1,0);
analyze table t1;
explain select * from t1
where (( f3 = 1 or f1 = 7 ) and f1 < 10) or
(f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
select * from t1
where (( f3 = 1 or f1 = 7 ) and f1 < 10) or
(f3 between 2 and 2 and ( f3 = 1 or f4 < 7 ));
drop table t0,t1;
set optimizer_switch= @optimizer_switch_save;
3 changes: 3 additions & 0 deletions sql/opt_range.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -7386,6 +7386,9 @@ static TRP_RANGE *get_key_scans_params(PARAM *param, SEL_TREE *tree,
found_records= check_quick_select(param, idx, read_index_only, key,
update_tbl_stats, &mrr_flags,
&buf_size, &cost, &is_ror_scan);
if (!is_ror_scan &&
!optimizer_flag(param->thd, OPTIMIZER_SWITCH_INDEX_MERGE_SORT_UNION))
continue;

if (found_records != HA_POS_ERROR && tree->index_scans &&
(index_scan= (INDEX_SCAN_INFO *)alloc_root(param->mem_root,
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