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HBase, mail # dev - About distributed lock service in HBase


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Re: About distributed lock service in HBase
Elliott Clark 2013-04-08, 18:54
1. Yes the region servers can absolutely work while the master is down (for
a while).  Master is mostly there for administrative clean up duties ie,
balancing, assigning and creating tables.  Additionally there can be more
than one master process running at a time.  There's a leader election that
takes place in zookeeper and when a master goes down any backup masters
will elect a new functioning master.

2.  We do use zookeeper for locks.
2.1 Trunk and 0.95.0 all use zookeeper for locking table operations.
See HBASE-7305
 as Ted suggests.
2.2 Row locks exposed to the user don't use zookeeper since only one region
server is ever responsible for a row.  With that said row locks are being
removed in HBASE-7315 since they didn't provide the guarantees that some
users were expecting (locks didn't survive region move or server restart)
On Mon, Apr 8, 2013 at 9:22 AM, Ted Yu <[EMAIL PROTECTED]> wrote:

> Brady:
> Hopefully Nicolas answered your questions.
>
> We do use zookeeper for coordinating table schema changes. See the
> following JIRA:
> HBASE-7305. ZK based Read/Write locks for table operations
>
> Cheers
>
> On Mon, Apr 8, 2013 at 8:34 AM, Nicolas Liochon <[EMAIL PROTECTED]> wrote:
>
> > HBASE-5541 is about rowlock. The master plays no role in this.  This lock
> > does not have to be distributed, because, in bigtable/hbase architecture,
> > the rows are allocated to a single region / region server. This makes
> > things faster.
> >
> > Nicolas
> >
> >
> > On Mon, Apr 8, 2013 at 5:27 PM, Brady Zhong <[EMAIL PROTECTED]
> > >wrote:
> >
> > > Hi Nicolas,
> > >
> > > Thanks for your explanation. I know HBase uses ZeeKeeper as coordinated
> > > service but not a lock management service like Chubby. Like HBASE-5541
> > > states, it seems the RegionServer controls the whole write process
> > > including providing row lock, region lock etc.. So I wonder why we
> don't
> > > use high available service like ZooKeeper creating, managing and
> > releasing
> > > lock?
> > >
> > >
> > > Brady
> > >
> > > On Mon, Apr 8, 2013 at 11:13 PM, Nicolas Liochon <[EMAIL PROTECTED]>
> > > wrote:
> > >
> > > > Hi,
> > > >
> > > > 1. Yes. Client applications can start/read/write even when there is
> no
> > > > master.
> > > > 2. HBase already uses ZooKeeper.
> > > >
> > > > You may want to have to look at the hbase reference guide (
> > > > http://hbase.apache.org/book.html).
> > > >
> > > > Nicolas
> > > >
> > > >
> > > > On Mon, Apr 8, 2013 at 4:39 PM, Brady Zhong <
> [EMAIL PROTECTED]
> > > > >wrote:
> > > >
> > > > > Hi all,
> > > > >
> > > > > My name is Brady Zhong, a college student using HBase to develop
> our
> > > own
> > > > > project. Currently I confronted with a problem. Since we need some
> > kind
> > > > of
> > > > > high availability, we hope HBase can keep available even though the
> > > > HMaster
> > > > > goes down. Here're my questions:
> > > > >
> > > > > 1. Can HBase work during the node failure of HMaster? Can users
> write
> > > or
> > > > > read the database before the switch and recovery of HMaster?
> > > > > 2. Why not use Zookeeper as distributed lock service for HBase,
> like
> > > > Chubby
> > > > > for Google Big Table?
> > > > >
> > > > > Thanks very much for any help in advance.
> > > > >
> > > > >
> > > > > Best regards,
> > > > > Brady Zhong
> > > > >
> > > >
> > >
> >
>