maria-developers team mailing list archive

[Sergei Golubchik <serg@xxxxxxxxxxx>]

Hi, Kentoku!

On Jun 06, kentoku wrote:
> 
> > > add checksum_null for setting null value of checksum
> > >
> > > diff --git a/sql/ha_partition.cc b/sql/ha_partition.cc
> > > index 4e7fccca3af..e47da94ab20 100644
> > > --- a/sql/ha_partition.cc
> > > +++ b/sql/ha_partition.cc
> > > @@ -8213,7 +8214,11 @@ int ha_partition::info(uint flag)
> > >        stats.delete_length+= file->stats.delete_length;
> > >        if (file->stats.check_time > stats.check_time)
> > >          stats.check_time= file->stats.check_time;
> > > -      stats.checksum+= file->stats.checksum;
> > > +      if (!file->stats.checksum_null)
> > > +      {
> > > +        stats.checksum+= file->stats.checksum;
> > > +        stats.checksum_null= FALSE;
> > > +      }
> >
> > I'm not sure about it. When a checksum can be NULL?
> >
> > I mean, normally, if you do A+B+C and one of the values is NULL,
> > then the whole sum is NULL. But here you simply skip NULLs, like in
> > aggregate SUM() function.
> >
> > To understand what semantics works better in this case, I need to
> > understand when a checksum can be NULL in spider.
> 
> Spider gets checksum from remote servers and Spider just uses this
> value. Some cases a checksum table command returns NULL from remote
> servers to Spider. Spider should use this result as is.  This is the
> reason that a checksum can be NULL in Spider.

So, looking at mysql_checksum_table(), CHECKSUM TABLE can be NULL in
three cases

* table doesn't exist
* one uses QUICK and the table doesn't support live checksum
* ha_rnd_init() failed, meaning, I presume, table is corrupted.

What would this mean for spider? If one of partitions is missing or
corrupted, the whole table is, basically, corrupted. Correct? So the
checksum should be NULL with an appropriate error message.

And I'd also say that in the second case - if some partitions support
live checksum and others don't - the table as a whole doesn't support
live checksum, so the result should be NULL as well.

That is, I think you should use the normall addition semantics, not the
aggregation semantics:

  stats.checksum_null= FALSE;
  ....
      if (file->stats.checksum_null)
        stats.checksum_null= TRUE;
      else
        stats.checksum+= file->stats.checksum;

Regards,
Sergei
Chief Architect MariaDB
and security@xxxxxxxxxxx