maria-developers team mailing list archive

[Sergei Petrunia <psergey@xxxxxxxxxxxx>]

Hi Zardosht,

On Fri, Feb 15, 2013 at 06:00:52PM -0500, Zardosht Kasheff wrote:
> On implementing this. Looking at MariaDB-5.5.28a, I see MyISAM,
> InnoDB, and Aria all have the code below in their engine.
> 
> Is that all that is required? Do we need to copy and paste that code
> into our engine? 

Generally, the answer depends on how you intend to implement MRR. As a
counter-example, NDB storage engine has its own MRR implementation that shares
no code with the Dsik-Sweep implementation of MRR that MyISAM/InnoDB/Aria are 
using (careful: NDB code in MariaDB is not maintained and is likely very out of 
date).

I don't know how MRR should be implemented for TokuDB (my exposure to TokuDB
has been limited to watching videos/slides). I guess, DS-MRR could be used as
a first approach.  But perhaps, a more advanced, specialized MRR implementation
is posisble.

> In fact, the only difference I see is that INnoDB
> has:
>   if (prebuilt->select_lock_type != LOCK_NONE)
>     *flags |= HA_MRR_USE_DEFAULT_IMPL;
> in multi_range_read_info_const.
> 

In case you decide to use DS-MRR: there are also ds_mrr.dsmrr_close() calls in 
several places. Your engine needs to make them, too.
It is also a good idea to set stats.mrr_length_per_rec, just like the other
engines doo.

> Thanks
> -Zardosht
> 
> The code:
> 
> int ha_maria::multi_range_read_init(RANGE_SEQ_IF *seq, void *seq_init_param,
>                                     uint n_ranges, uint mode,
>                                     HANDLER_BUFFER *buf)
> {
>   return ds_mrr.dsmrr_init(this, seq, seq_init_param, n_ranges, mode, buf);
> }
> 
> int ha_maria::multi_range_read_next(range_id_t *range_info)
> {
>   return ds_mrr.dsmrr_next(range_info);
> }
> 
> ha_rows ha_maria::multi_range_read_info_const(uint keyno, RANGE_SEQ_IF *seq,
>                                                void *seq_init_param,
>                                                uint n_ranges, uint *bufsz,
>                                                uint *flags, COST_VECT *cost)
> {
>   /*
>     This call is here because there is no location where this->table would
>     already be known.
>     TODO: consider moving it into some per-query initialization call.
>   */
>   ds_mrr.init(this, table);
>   return ds_mrr.dsmrr_info_const(keyno, seq, seq_init_param, n_ranges, bufsz,
>                                  flags, cost);
> }
> 
> ha_rows ha_maria::multi_range_read_info(uint keyno, uint n_ranges, uint keys,
>                                        uint key_parts, uint *bufsz,
>                                        uint *flags, COST_VECT *cost)
> {
>   ds_mrr.init(this, table);
>   return ds_mrr.dsmrr_info(keyno, n_ranges, keys, key_parts, bufsz,
> flags, cost);
> }
> 
> int ha_maria::multi_range_read_explain_info(uint mrr_mode, char *str,
>                                             size_t size)
> {
>   return ds_mrr.dsmrr_explain_info(mrr_mode, str, size);
> }
> 
> On Fri, Feb 15, 2013 at 5:17 PM, Igor Babaev <igor@xxxxxxxxxxxx> wrote:
> > On 02/15/2013 04:17 AM, Zardosht Kasheff wrote:
> >> Hello all,
> >>
> >> Is there anything to implementing multi range read for storage
> >> engines? Or is there a default implementation that is likely good
> >> enough.
> >>
> >> Also, is there anything one can read to understand how the feature
> >> works and its benefits?
> >>
> >> Thanks
> >> -Zardosht
> >
> > Hi Zardosht,
> >
> > I googled "MySQL Multi Range Read" and got
> > among other references:
> >
> > 1. https://kb.askmonty.org/en/multi-range-read-optimization/
> >
> > 2. http://dev.mysql.com/doc/refman/5.6/en/mrr-optimization.html
> >
> > The first article was written by Sergey Petrunia, the guy who wrote
> > disk-sweep MRR.
> > I find it the most comprehensive.
> >
> > The second article was written also by him but when he worked at Sun.
> > Later this article was slightly changed by MySQL/Oracle people.
> >
> > Regards,
> > Igor.
> >
> >>
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> 
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-- 
BR
 Sergei
-- 
Sergei Petrunia, Software Developer
Monty Program AB, http://askmonty.org
Blog: http://s.petrunia.net/blog