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create database explain_test_db;
create table explain_test_db.explain_test_table (c int);
lock table explain_test_db.explain_test_table write;
# Connection con1
insert into explain_test_db.explain_test_table values ('1');
# Connection default
select OBJECT_INSTANCE_BEGIN, NAME, LOCKED_BY_THREAD_ID
from performance_schema.mutex_instances
where LOCKED_BY_THREAD_ID is not NULL
limit 1
into @oib, @name, @lbtid;
====================================================================
Testing index for columns OBJECT_INSTANCE_BEGIN
====================================================================
############ Explain for Query ####################################
explain select count(*)
from performance_schema.mutex_instances
where OBJECT_INSTANCE_BEGIN = "impossible";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL # NULL no matching row in const table
############ Explain for Query ####################################
explain select count(*)
from performance_schema.mutex_instances
where OBJECT_INSTANCE_BEGIN > "impossible";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE mutex_instances NULL ALL PRIMARY NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.mutex_instances
where OBJECT_INSTANCE_BEGIN < "2";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE mutex_instances NULL ALL PRIMARY NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.mutex_instances
where OBJECT_INSTANCE_BEGIN = @oib;
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE mutex_instances NULL const PRIMARY PRIMARY 8 const # 100.00 NULL
############# Explain End #########################################
flush status;
select count(*)
from performance_schema.mutex_instances
where OBJECT_INSTANCE_BEGIN = @oib;
count(*)
#
OK: handler_read_key incremented
====================================================================
Testing index for columns NAME
====================================================================
############ Explain for Query ####################################
explain select count(*)
from performance_schema.mutex_instances
where NAME = "impossible";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE mutex_instances NULL ref NAME NAME 514 const # 100.00 NULL
############ Explain for Query ####################################
explain select count(*)
from performance_schema.mutex_instances
where NAME > "impossible";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE mutex_instances NULL ALL NAME NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.mutex_instances
where NAME < "2";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE mutex_instances NULL ALL NAME NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.mutex_instances
where NAME = @name;
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE mutex_instances NULL ref NAME NAME 514 const # 100.00 NULL
############# Explain End #########################################
flush status;
select count(*)
from performance_schema.mutex_instances
where NAME = @name;
count(*)
#
OK: handler_read_key incremented
====================================================================
Testing index for columns LOCKED_BY_THREAD_ID
====================================================================
############ Explain for Query ####################################
explain select count(*)
from performance_schema.mutex_instances
where LOCKED_BY_THREAD_ID = "impossible";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE mutex_instances NULL ref LOCKED_BY_THREAD_ID LOCKED_BY_THREAD_ID 9 const # 100.00 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.mutex_instances
where LOCKED_BY_THREAD_ID > "impossible";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE mutex_instances NULL ALL LOCKED_BY_THREAD_ID NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.mutex_instances
where LOCKED_BY_THREAD_ID < "2";
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE mutex_instances NULL ALL LOCKED_BY_THREAD_ID NULL NULL NULL # 33.33 Using where
############ Explain for Query ####################################
explain select count(*)
from performance_schema.mutex_instances
where LOCKED_BY_THREAD_ID = @lbtid;
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE mutex_instances NULL ref LOCKED_BY_THREAD_ID LOCKED_BY_THREAD_ID 9 const # 100.00 NULL
############# Explain End #########################################
flush status;
select count(*)
from performance_schema.mutex_instances
where LOCKED_BY_THREAD_ID = @lbtid;
count(*)
#
OK: handler_read_key incremented
unlock tables;
# connection con1
# connection default
drop table explain_test_db.explain_test_table;
drop database explain_test_db;
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