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Message #06404
EXPLAIN in the slow query log
Hello,
After recent changes in the [SHOW] EXPLAIN architecture in MariaDB, it became
really easy to add an option to print EXPLAIN(*) output into the slow query log,
so I went ahead and implemented it.
@@log_slow_verbosity has got a 'explain' flag, and if it is on, the slow query
log entries look like this:
# Time: 131017 21:26:02
# User@Host: root[root] @ localhost []
# Thread_id: 2 Schema: dbt3sf1 QC_hit: No
# Query_time: 5.535819 Lock_time: 0.000350 Rows_sent: 1 Rows_examined: 65633
## <explain>
## id select_type table type possible_keys key key_len ref rows Extra
## 1 SIMPLE nation ref PRIMARY,n_name n_name 26 const 1 Using where; Using index
## 1 SIMPLE customer ref PRIMARY,i_c_nationkey i_c_nationkey 5 dbt3sf1.nation.n_nationkey 25124 Using index
## 1 SIMPLE orders ref i_o_custkey i_o_custkey 5 dbt3sf1.customer.c_custkey 7 Using index
## </explain>
SET timestamp=1382030762;
select count(*) from customer, orders, nation where c_custkey=o_custkey and c_nationkey=n_nationkey and n_name='GERMANY';
It seems, pt-slow-query-log has no problem parsing this.
Open questions:
- Is this syntax OK?
- Currently, some statements (like SHOW KEYS) print a dumb explain that
shows that full table scan is used. There is a suggestion to not print
EXPLAIN for any SHOW statements. Is this ok?
(*) something like EXPLAIN ANALYZE, with numbers from actual execution, would
be better but we are not there yet.
BR
Sergei
--
Sergei Petrunia, Software Developer
MariaDB | Skype: sergefp | Blog: http://s.petrunia.net/blog
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