maria-developers team mailing list archive

[kentoku <kentokushiba@xxxxxxxxx>]

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?

> - 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.

> - 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@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
>> > >
>>
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>
>
>
> --
> Roberto Spadim
> SPAEmpresarial
>