I don't understand why you need both the <explain> xml style tag and
the double # to denote an explain entry. I would prefer to see each
line prefixed with # explain: to make it similar to the other info
lines above and get rid of the <explain>.

By prefixing each line with # explain: it makes grepping explain plans
easier than looking for a start and end tag on different lines.

On Fri, Oct 18, 2013 at 4:59 PM, Sergei Golubchik <serg@mariadb.org> wrote:
> Hi, Sergei!
>
> On Oct 18, Sergei Petrunia wrote:
>> 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?
>
> Yes, assuming you use tabs as column separators, not spaces.
>
>> - 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?
>
> Yes. If users will complain we can always change it back later.
>
> Regards,
> Sergei
>
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--
Eric Bergen
eric.bergen@gmail.com
http://www.ebergen.net

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