2013/11/7 Sergey Vojtovich <svoj@mariadb.org>

Kentoku,

please find iterator prototype attached. I didn't test it.

Regards,
Sergey

On Thu, Nov 07, 2013 at 03:18:04PM +0400, Sergey Vojtovich wrote:
> Hi Kentoku,
>
> thanks for implementing these requests. Technically it looks much better now.
> Though I believe it is a good idea to keep mdl private classes private. I think
> we should add logics of i_s_metadata_lock_info_fill_table() to mdl.cc. I'll do
> that and get back to you when ready.
>
> More comments inline.
>
> On Fri, Nov 01, 2013 at 05:28:32AM +0900, kentoku wrote:
> > Hi Sergey and Roberto,
> >
> > Thank you for reviewing and suggesting!
> > Currently, branch is the following.
> > lp:~kentokushiba/maria/10.0.4-metadata_lock_info
> >
> > > 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);
> >
> > Fixed.
> >
> > > 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)
> >
> > Fixed.
> >
> > > - why check for thd->killed?
> > > (shouldn't be relevant anymore)
> >
> > Fixed.
> >
> > > - 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()
> > > ...
> > > };
> >
> > Fixed.
> >
> > > - Roberto suggests to rename ID to THREAD_ID and I agree
> >
> > Fixed.
> >
> > > - Roberto suggests to add QUERY_ID column and I agree
> >
> > Not fixed. Where can I get locker's QUERY_ID?
> It is mdl_ctx->get_owner()->get_thd()->query_id.
>
> >
> > > - Roberto suggests to add LOCK_DURATION column and I agree
> >
> > Fixed. If calling find_ticket() for getting LOCK_DURATION is costly, I will
> > change it. Please review it.
> It's a bit heavy indeed. What is the other option you're considering?
>
> Regards,
> Sergey
>
> >
> > > - 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().
> >
> > Fixed.
> >
> > > - 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.
> >
> > Fixed.
> >
> > Thanks,
> > Kentoku
> >
> >
> > 2013/10/30 Roberto Spadim <roberto@spadim.com.br>
> >
> > > =) no problem about disagree, i'm agree now hehe
> > > thanks guys! :)
> > >
> > >
> > > 2013/10/29 Sergey Vojtovich <svoj@mariadb.org>
> > >
> > >> 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@gmail.com>
> > >> >
> > >> > > 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@lists.launchpad.net
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> > >>
> > >
> > >
> > >
> > > --
> > > Roberto Spadim
> > > SPAEmpresarial
> > >
>
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