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From Ted Yu <yuzhih...@gmail.com>
Subject Re: help, try to use HBase's checkAndPut() to implement distribution lock
Date Wed, 10 Aug 2016 14:16:51 GMT
Please take a look at EnableTableHandler where you can find example
- prepare() and process().

On Tue, Aug 9, 2016 at 5:04 PM, Liu, Ming (Ming) <ming.liu@esgyn.cn> wrote:

> Thanks Ted for pointing out this. Can this TableLockManager be used from a
> client? I am fine to migrate if this API change for each release.
> I am writing a client application, and need to lock a hbase table, if this
> can be used directly, that will be super great!
>
> Thanks,
> Ming
>
> -----Original Message-----
> From: Ted Yu [mailto:yuzhihong@gmail.com]
> Sent: Wednesday, August 10, 2016 1:04 AM
> To: user@hbase.apache.org
> Subject: Re: help, try to use HBase's checkAndPut() to implement
> distribution lock
>
> Please take a look at TableLockManager and its subclasses.
>
> It is marked @InterfaceAudience.Private
> Meaning the API may change across releases.
>
> Cheers
>
> On Tue, Aug 9, 2016 at 9:58 AM, Liu, Ming (Ming) <ming.liu@esgyn.cn>
> wrote:
>
> > Thanks Ted for the questions.
> >
> > 1. what if the process of owner of the lock dies?
> > I didn't think of this... This is really an issue. I don't have a good
> > answer. One possibility is to have a lease of each lock, owner must
> > renew it periodically until release it. The getLock can check the last
> > timestamp to see if it is expired. But I have no idea how the lock
> > owner can periodic renew the lock lease, spawn a new thread to do
> > that? So, this makes me trying to abandon this idea.
> >
> > 2. How can other processes obtain the lock?
> > The getLock() has input param of table, so any process can give the
> > tablename and invoke getLock(), it check the row 0 value in an atomic
> > check and put operation. So if the 'table lock' is free, anyone should
> > be able to get it I think.
> >
> > Maybe I have to study the Zookeeper's distributed lock recipes?
> >
> > Thanks,
> > Ming
> >
> > -----Original Message-----
> > From: Ted Yu [mailto:yuzhihong@gmail.com]
> > Sent: Wednesday, August 10, 2016 12:26 AM
> > To: user@hbase.apache.org
> > Subject: Re: help, try to use HBase's checkAndPut() to implement
> > distribution lock
> >
> > What if the process of owner of the lock dies ?
> > How can other processes obtain the lock ?
> >
> > Cheers
> >
> > On Tue, Aug 9, 2016 at 8:19 AM, Liu, Ming (Ming) <ming.liu@esgyn.cn>
> > wrote:
> >
> > > Hi, all,
> > >
> > > I want to implement a simple 'table lock' in HBase. My current idea
> > > is for each table, I choose a special rowkey which NEVER be used in
> > > real data, and then use this row as a 'table level lock'.
> > >
> > > The getLock() will be:
> > >
> > >   getLock(table, cf, cl)
> > >   {
> > >      rowkey = 0 ; //which never used in real data
> > >
> > >     //generate a UUID, thread ID + an atomic increamental sequence
> > > number for example. Call it myid
> > >      genMyid(myid);
> > >
> > >      while(TRUE)
> > >      {
> > >          ret = table.checkAndPut ( rowkey, cf , cl , '0' , myid);
> > >          if (ret == true ) get the lock
> > >              return myid;
> > >          else
> > >              sleep and continue; //retry, maybe can retry for
> > > timeout here, or wait forever here
> > >       }
> > >    }
> > >
> > > The releaseLock() may be:
> > >
> > >    releaseLock(table, cf, cl, myid)
> > >    {
> > >        Rowkey = 0;
> > >         ret = checkAndPut ( rowkey , cf , cl , myid , '0' );  //If I
> > > am holding the lock
> > >         if (ret == TRUE) return TRUE;
> > >         else  return FALSE;
> > >  }
> > >
> > > So one caller get lock, and others must wait until the caller
> > > release it, and only the lock holder can release the lock. So if one
> > > getLock(), it can then modify the table, others during this period
> > > must
> > wait.
> > >
> > > I am very new in lock implementation, so I fear there are basic
> > > problems in this 'design'.
> > > So please help me to review if there are any big issues about this
> idea?
> > > Any help will be very appreciated.
> > >
> > > Thanks a lot,
> > > Ming
> > >
> >
>

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