maria-developers team mailing list archive

[Sergei Golubchik <serg@xxxxxxxxxxxx>]

Hi, Alexey!

On May 16, Alexey Botchkov wrote:
> Sergei,
> 
> 
> 11.05.2012 19:44, Sergei Golubchik wrote:
> > === modified file 'mysql-test/r/read_only.result'
> > --- a/mysql-test/r/read_only.result	2009-03-06 14:56:17 +0000
> > +++ b/mysql-test/r/read_only.result	2012-05-09 18:59:45 +0000
> > @@ -59,7 +59,7 @@
> >   connection con1;
> >   select @@global.read_only;
> >   @@global.read_only
> > -0
> > +1
> > This is prone to race conditions.
> > Please, fix the test to remove "send" here and below.
> > (assuming the new result is correct)
> 
> >
> > But is it correct ?
> > Why set read_only is not blocked by a write locked myisam table?
> 
> It's not blocked as we ceased incrementing the refresh_version in this case:

Okay. But is it correct?
Can you try the following:

  1st client: LOCK TABLE t1 WRITE;
  2nd client: SET READ_ONLY=1;
  1st client: INSERT t1 VALUES (1);

> >> === modified file 'sql/sql_base.cc'
> >> --- a/sql/sql_base.cc	2012-04-19 06:16:30 +0000
> >> +++ b/sql/sql_base.cc	2012-05-09 18:59:45 +0000
> >> @@ -933,7 +938,8 @@
> >>         for (uint idx=0 ; idx<  open_cache.records ; idx++)
> >>         {
> >>           TABLE *table=(TABLE*) hash_element(&open_cache,idx);
> >> -        if (table->in_use)
> >> +        if (table->in_use&&
> >> +            (!set_readonly_mode || !table->file->has_transactions()))
> > I wonder how this could work. The line below sets a flag *on a thread*.
> > The task description tells "not wait for transactional tables", while your
> > change means "not set a flag if all tables used in a thread are
> > transactional". That is, if a thread uses both transactional and
> > non-transactional tables, your change does nothing.
> 
> That's right, it' won't work with the mixed types of tables.
> But as the customer didn't ask for that, maybe the simplest solution 
> will do here.

I'm not sure about it. It's basically a gotcha. "SET READ_ONLY will not
flush transactional tables, but only if the statement uses no
non-transactional tables. Otherwise it'll flush all tables,
transactional or not". One cannot always know if non-transactional
tables are involved. Think of log tables, tables used in triggers and
stored routines.

Regards,
Sergei