maria-discuss team mailing list archive

[Igor Babaev <igor@xxxxxxxxxxxx>]

Peter,

You are right that EXPLAIN in any format has nothing to do with the
optimizer. Looking at the piece of the MySQL code that forms the strings
for the EXPLAIN anyone could easily come up with the patch providing
JSON format for the EXPLAIN (even with the extensions of MySQL 5.6) and
it would take him/her 2-3 days at most (maybe even a few hours).

That's why we are reluctant to pull the existing implementation of JSON
format from MySQL 5.6 into MariaDB. The patch is huge and overburdened
with unneeded complexities. Besides it contains a lot of "restructuring"
code that has nothing to do with the feature itself.

Personally I think that the content in the current EXPLAIN (including
the content of the EXPLAIN EXTENDED) is so shallow that any graphical
representation hardly can help it (compare it, for example, with the
info provided by MS SQL server).

If, nevertheless, you badly need the feature and is ready to co-sponsor
the feature (together with MP AB) we could discuss the details of the
possible simple implementation. And of course we will support it in
MariaDB if anybody else provide us with a patch for such an implementation.

Regards,
Igor.

On 09/30/2012 04:23 AM, Peter Laursen wrote:
> I do not see why this should be a concern for the optimizer team.
> 
> The output from EXPLAIN (in any format) does not affect optimizer's
> operation but only provides information of *optimizer result*. The
> format chosen is (?) applied is *after* not *before* or *during* the
> optimization process.
> 
> TRADITIONAL EXPLAIN returns the result as an **array**.  JSON EXPLAIN
> returns the result as a single (Json-formatted) **string** (not unlike
> SHOW ENGINE INNODB STATUS, btw).  But both should have exactly the same
> information - and if they don't it is a bug with JSON EXPLAIN in MySQL
> 5.6 IMO.
> 
> But as I am not well-versed in server internals, I could have
> ovelooked/misunderstood something, of course.
> 
> -- Peter
> 
> On Fri, Sep 28, 2012 at 5:18 PM, Peter Laursen <peter_laursen@xxxxxxxxxx
> <mailto:peter_laursen@xxxxxxxxxx>> wrote:
> 
>     @wlad is completely right!
> 
>     Workbench introduced a Visual Explain based on JSON EXPLAIN as
>     Blogged here:
>     http://www.arubin.org/blog/2012/09/26/mysql-visual-explain/
> 
>     The very reason why JSON EXPLAIN was introduced in MySQL 5.6 could
>     be that Oracle develops the server and tools (WB, Enterprirse
>     Monitor primarily) in parallel.  Some recently introduced features
>     in the server could be introduced for the primary reason that they
>     should be 'exploited' by MEM and/or WB.  JSON EXPLAIN is one.
>     Another example is the Performance_Schema table introduced in 5.6.6
>     (I don't remember the table name)  that records an 'aggregated
>     summary' of queries' performance. Actually this table has about the
>     same information as what MONyog 'Query Analyzer' module displays in
>     its most simple display mode (but MONyog can be 'drilled down' to a
>     more detailed view). 
> 
>     So Oracle *thinks* the server and their most important tools *as a
>     whole*, I think. We/Webyog cannot ignore this, as we compete with
>     Oracle (SQLyog <-> WB, MONyog <-> MEM).  We have to consider to
>     implement a more intuitive and advisory way of displaying EXPLAIN
>     results (for non-expert users primarily of course). The JSON format
>     is interesting for us in the context.
> 
>     -- Peter
> 
> 
> 
> 
> 
>     On Fri, Sep 28, 2012 at 4:50 PM, Vladislav Vaintroub
>     <wlad@xxxxxxxxxxxxxxxx <mailto:wlad@xxxxxxxxxxxxxxxx>> wrote:
> 
> 
> 
>         > -----Original Message-----
>         > From: maria-discuss-
>         > bounces+wlad=montyprogram.com@xxxxxxxxxxxxxxxxxxx
>         <mailto:montyprogram.com@xxxxxxxxxxxxxxxxxxx> [mailto:maria-
>         <mailto:maria->
>         > discuss-bounces+wlad=montyprogram.com@xxxxxxxxxxxxxxxxxxx
>         <mailto:montyprogram.com@xxxxxxxxxxxxxxxxxxx>] On Behalf
>         > Of Michael Widenius
>         > Sent: Freitag, 28. September 2012 16:04
>         > To: Peter Laursen; igor@xxxxxxxxxxxx
>         <mailto:igor@xxxxxxxxxxxx>; timour@xxxxxxxxxxxx
>         <mailto:timour@xxxxxxxxxxxx>;
>         > psergey@xxxxxxxxxxxx <mailto:psergey@xxxxxxxxxxxx>
>         > Cc: Maria Discuss; Maria Developers
>         > Subject: Re: [Maria-discuss] [Maria-developers] Json Explain
>         >
>         >
>         > For the moment we don't have a plan for that.
>         >
>         > The main reason is that the MariadB optimizer people don't
>         like the
>         > implementation and we are not sure how useful the current output
>         > really is.
>         >
> 
>         I guess json  is not for normal people to read , it is for
>         programs to
>         analyze and ,for example, display in a visually pleasing
>         fashion. I believe
>         this is the reason why Peter asks, and (I guess) the reason why
>         Workbench
>         has visual explain feature now for 5.6+.
>         http://www.arubin.org/blog/2012/09/26/mysql-visual-explain/
> 
> 
>