maria-developers team mailing list archive

[Elena Stepanova <elenst@xxxxxxxxxxxxxxxx>]

Hi,

On 10/19/2013 7:26 PM, Eric Bergen wrote:
> 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>.

Regardless the <explain> tags (it's a different story), it was my 
suggestion to go with double ## rather than with '# explain' which 
Sergei actually suggested himself. It seems to me that it's just as easy 
to grep for '^##' as it is for '# explain:', while the variant with 
double # is less excessive and more readable when you just look through 
the log without pre-grepping.

I don't insist on the above though, if those who care prefer the prefix 
with '# explain:' :)

Regards,
Elena

> 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@xxxxxxxxxxx> 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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