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From Gregory Chanan <gcha...@cloudera.com>
Subject Re: 0.92/0.94 compatibility and HBASE-5206
Date Sat, 01 Sep 2012 00:54:22 GMT
Actually, I think we can make 0.94.2 compatible with both {0.94.0,0.94.1}
and {0.92.0,0.92.1}, although one of those sets will require configuration
changes.

The basic problem is that there is a znode for each table
"zookeeper.znode.tableEnableDisable" that is handled differently.

On 0.92.0 and 0.92.1 the states for this table are:
[ disabled, disabling, enabling ] or deleted if the table is enabled

On 0.94.1 and 0.94.2 the states for this table are:
[ disabled, disabling, enabling, enabled ]

What saves us is that the location of this znode is configurable.  So the
basic idea is to have the 0.94.2 master write two different znodes,
"zookeeper.znode.tableEnableDisabled92" and
"zookeeper.znode.tableEnableDisabled94" where the 92 node is in 92 format,
the 94 node is in 94 format.  And internally, the master would only use the
94 format in order to solve the original bug HBASE-5155 solves.
We can of course make one of these the same default as exists now, so we
don't need to make config changes for one of 0.92 or 0.94 clients.  I argue
that 0.92 clients shouldn't have to make config changes for the same reason
I argued above.  But that is debatable.

Then, I think the only question left is Stack's question of how to bring
along the {0.94.0, 0.94.1} crew.  A {0.94.0, 0.94.1} client would work
against a 0.94.2 cluster by just
configuring "zookeeper.znode.tableEnableDisable" in the client to be
whatever "zookeeper.znode.tableEnableDisabled94" is in the cluster.  A
0.94.2 client would work against both a {0.94.0, 0.94.1} and {0.92.0,
0.92.1} cluster if it had HBASE-6268 applied.  About rolling upgrade from
{0.94.0, 0.94.1} to 0.94.2 -- I'd have to think about that.  Do the
regionservers ever read the tableEnableDisabled znode?

Greg

On Fri, Aug 31, 2012 at 4:41 PM, lars hofhansl <lhofhansl@yahoo.com> wrote:

> I guess you voiced your opinion in your initial email already (you prefer
> to break compatibility between 0.94.0/0.94.1 with 0.94.2).
> If that is indeed the consensus, please file a jira against 0.94.2.
>
> -- Lars
>
>
>
> ----- Original Message -----
> From: lars hofhansl <lhofhansl@yahoo.com>
> To: "dev@hbase.apache.org" <dev@hbase.apache.org>
> Cc:
> Sent: Friday, August 31, 2012 4:24 PM
> Subject: Re: 0.92/0.94 compatibility and HBASE-5206
>
> What do you think we should do?
>
> 1. Breaking compatibility between minor versions is bad. (i.e. we should
> fix this in 0.92.2 as currently proposed)
> 2. At the same time 0.92 might be in wider distribution and that the
> upgrade path 0.94 might be more important (and include the fix that you
> propose).
>
> I'm +1 on #1 and +0 on #2.
>
>
> I agree we need better cross-version integration testing and be generally
> more diligent about this.
>
> -- Lars
> ________________________________
> From: Gregory Chanan <gchanan@cloudera.com>
> To: dev@hbase.apache.org
> Cc: lars hofhansl <lhofhansl@yahoo.com>
> Sent: Friday, August 31, 2012 4:06 PM
> Subject: Re: 0.92/0.94 compatibility and HBASE-5206
>
> @Lars:
> you are correct that this would break compatibility between {0.94.0,
> 0.94.1} and 0.94.2.
>
> We clearly need better compatibility testing, these issues are hard to find
> by just looking at patches.
>
> Greg
>
> On Fri, Aug 31, 2012 at 4:03 PM, Ted Yu <yuzhihong@gmail.com> wrote:
>
> > I should also apologize for HBASE-5206 where I didn't maintain
> > compatibility in the first place.
> >
> > We just need to find the solution which minimizes impact of this issue.
> >
> > Cheers
> >
> > On Fri, Aug 31, 2012 at 3:55 PM, lars hofhansl <lhofhansl@yahoo.com>
> > wrote:
> >
> > > Won't we then break compatibility between 0.94.0 and 0.94.1 with
> 0.94.2?
> > > I do not have a strong opinion about this.
> > >
> > > It was my fault that HBASE-5206 slipped into 0.94.0, I apologize for
> > that.
> > >
> > > I was going to spin the first 0.94.2 today. Is the general consensus
> that
> > > I should wait?
> > >
> > >
> > > -- Lars
> > >
> > >
> > >
> > > ________________________________
> > >  From: Gregory Chanan <gchanan@cloudera.com>
> > > To: dev@hbase.apache.org
> > > Sent: Friday, August 31, 2012 3:13 PM
> > > Subject: 0.92/0.94 compatibility and HBASE-5206
> > >
> > > There has been some discussion on the JIRA lately about what to do
> about
> > a
> > > 0.92/0.94 compatibility issue.  I wanted to bring this up to a larger
> > > audience in order to solicit additional opinions.
> > >
> > > HBASE-5206 (https://issues.apache.org/jira/browse/HBASE-5206), which
> is
> > in
> > > 0.94.0 and 0.94.1, breaks compatibility with 0.92.0 and 0.92.1.  The
> > issue
> > > is described in the release notes for HBASE-5155 (of which HBASE-5206
> is
> > a
> > > forward port).  Excerpted here:
> > >
> > >   This issue is an incompatible change.
> > >   If an HBase client with the changes for HBASE-5155 and a server
> > (master)
> > > without the changes for HBASE-5155 is used, then the is_enabled (from
> > HBase
> > > Shell) or isTableEnabled() (from HBaseAdmin) will return false though
> the
> > > table is already enabled as per the master.
> > >
> > >   If the HBase client does have the changes for HBASE-5155 and the
> server
> > > does not have the changes for HBASE-5155, then if we try to Enable a
> > table
> > > then the client will hang.
> > >
> > >   The reason is because,
> > >   Prior to HBASE-5155 once the table is enabled the znode in the
> > zookeeper
> > > created for the table is deleted.
> > >   After HBASE-5155 once the table is enabled the znode in the zookeeper
> > > created for the table is not deleted, whereas the same node is updated
> > with
> > > the status ENABLED.
> > >
> > >   The client also expects the status of the znode in the zookeeper to
> be
> > in
> > > the ENABLED state if the table has been enabled successfully.
> > >   The above changes makes the client behaviour incompatible if the
> client
> > > does not have this fix whereas the server has this fix.
> > >   If both the client and the server does not have this fix, then the
> > > behaviour is as expected.
> > >
> > > So we have a situation where 0.92.0 and 0.92.1 clients are not
> compatible
> > > with 0.94.0 and 0.94.1 servers and visa-versa.
> > >
> > > The issue is, what should we do about the 0.94.2 server?  As far as I
> can
> > > tell, we cannot make both {0.92.0,0.92.1} and {0.94.0,0.94.1} clients
> > > happy.  I propose we make the 0.94.2 server compatible with the
> {0.92.0,
> > > 0.92.1} client set.  My thinking is that we should optimize for the
> most
> > > common use case.  Given that both CDH4 and HDP 1.0 ship 0.92.1, and
> that
> > > 0.94 is relatively new, it seems more likely that users will upgrade
> > > servers from 0.92.1 to 0.94.2+ than from an earlier 0.94 version.  I
> > think
> > > we can do this while actually fixing the issue that HBASE-5206 purports
> > to
> > > fix by moving the ENABLED state to a different znode.  I'll even
> > volunteer
> > > to do that :).  I don't think there is an obvious or easy answer here,
> so
> > > wanted to get other's opinions.
> > >
> > > As for the client, HBASE-6268 (
> > > https://issues.apache.org/jira/browse/HBASE-6268) was introduced in
> > 0.92.2
> > > to handle both cases of servers ({0.92.0,0.92.1} and {0.94.0,0.94.1})
> by
> > > accepting both possibilities for the table znode.  I think that
> approach
> > > works whether we leave the server as is or go with what I've proposed
> --
> > > but we should test.
> > >
> > > Greg
> >
>
>

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