maria-developers team mailing list archive

[Roberto Spadim <roberto@xxxxxxxxxxxxx>]

=) no problem about disagree, i'm agree now hehe
thanks guys! :)


2013/10/29 Sergey Vojtovich <svoj@xxxxxxxxxxx>

> Hi Kentoku,
>
> thanks for your contribution and sorry for this long delay. I finally
> managed
> to go through your code.
>
> The most important thing I'm worried about is that there is no protection
> of ticket lists: lists may be updated while we iterate them and it may
> cause
> server crash in concurrent environment. From what I can see MDL_context is
> mostly supposed to be accessed only by thread which owns this context. As
> such
> it is not protected by any locks.
>
> I believe we should use global lists instead, something like:
>   mysql_mutex_lock(&mdl_locks.m_mutex);
>   iterate mdl_locks.m_locks (hash of MDL_lock)
>   {
>     mysql_prlock_rdlock(&lock->m_rwlock);
>     iterate lock->m_granted (list of MDL_ticket)
>     {
>       // store data
>     }
>     mysql_prlock_unlock(&lock->m_rwlock);
>   }
>   mysql_mutex_lock(&mdl_locks.m_mutex);
>
> A few more suggestions in no particular order:
> - instead of making m_tickets public I'd suggest to try to make
>   i_s_metadata_lock_info_fill_table() a friend function
>   (shouldn't be relevant anymore)
>
> - why check for thd->killed?
>   (shouldn't be relevant anymore)
>
> - metadata_lock_info_lock_mode_length[] includes ending zero, and then
>   we store e.g. "MDL_SHARED\0" whereas we should store "MDL_SHARED"
>
>   I'd suggest to declare these arrays as following:
>   static const LEX_STRING metadata_lock_info_lock_mode_str[]=
>   {
>     STRING_WITH_LEN("MDL_INTENTION_EXCLUSIVE"), // or C_STRING_WITH_LEN()
>     ...
>   };
>
> - Roberto suggests to rename ID to THREAD_ID and I agree
> - Roberto suggests to add QUERY_ID column and I agree
> - Roberto suggests to add LOCK_DURATION column and I agree
> - Roberto suggests to use m_namespace_to_wait_state_name instead of
>   metadata_lock_info_lock_names, but I tend to disagree because the former
> says
>   "Waiting for...". Though I'd suggest to make array of LEX_STRING's to
> avoid
>   calling strdup().
>
> - Roberto suggests to replace DB with KEY and NAME with SUB_KEY, but I
> tend to
>   disagree since in most cases it is db and table name. I'd vote for
>   TABLE_SCHEMA and TABLE_NAME to stay in line with the rest I_S tables.
>
> Regards,
> Sergey
>
> On Mon, Jul 01, 2013 at 03:46:22AM +0900, kentoku wrote:
> > Hi Sergey,
> > Sorry. I think this plugin needs more locks "mdl_locks.m_mutex",
> > "mdl_locks.m_global_lock" and "mdl_locks.m_commit_lock". Is it right?
> Would
> > you please teach me how can I use it?
> > Thanks,
> > Kentoku
> >
> >
> > 2013/7/1 kentoku <kentokushiba@xxxxxxxxx>
> >
> > > Hi Sergey,
> > >
> > > I made new information schema plugin which named "metadata_lock_info"
> > > plugin. This plugin makes it possible knowing "who has metadata
> locks". In
> > > development stage, sometimes DBAs meet metadata locks when using alter
> > > table statement. This metadata locks are sometimes caused by GUI
> tools. In
> > > service stage, sometimes DBAs meet metadata locks when using alter
> table
> > > statement. This metadata locks are sometimes caused by long batch
> > > processing. In many cases, the DBAs need to judge immediately. So I
> made it
> > >  for all DBAs.
> > > Would you please review this plugin?
> > > lp:~kentokushiba/maria/10.0.3-metadata_lock_info
> > > Note: This plugin needs a change of sql/mdl.h
> > >
> > > Thanks,
> > > Kentoku
> > >
>
> _______________________________________________
> Mailing list: https://launchpad.net/~maria-developers
> Post to     : maria-developers@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~maria-developers
> More help   : https://help.launchpad.net/ListHelp
>



-- 
Roberto Spadim
SPAEmpresarial