EXPLAIN in the Slow Query Log
Switching it On
EXPLAIN output will only be recorded if the slow query log is written to a file (and not to a table - see Writing logs into tables). This limitation also applies to other extended statistics that are written into the slow query log.
What it Looks Like
When explain recording is on, slow query log entries look like this:
# Time: 131112 17:03:32 # User@Host: root[root] @ localhost  # Thread_id: 2 Schema: dbt3sf1 QC_hit: No # Query_time: 5.524103 Lock_time: 0.000337 Rows_sent: 1 Rows_examined: 65633 # # explain: id select_type table type possible_keys key key_len ref rows Extra # explain: 1 SIMPLE nation ref PRIMARY,n_name n_name 26 const 1 Using where; Using index # explain: 1 SIMPLE customer ref PRIMARY,i_c_nationkey i_c_nationkey 5 dbt3sf1.nation.n_nationkey 3145 Using index # explain: 1 SIMPLE orders ref i_o_custkey i_o_custkey 5 dbt3sf1.customer.c_custkey 7 Using index # SET timestamp=1384261412; select count(*) from customer, orders, nation where c_custkey=o_custkey and c_nationkey=n_nationkey and n_name='GERMANY';
EXPLAIN lines start with